Salinity management handbook Second edition
Tomorrow’s Queensland: strong, green, smart, healthy and fair ISBN 0 7242 7412 X DNRQ97109 #28823
National Library of Australia Cataloguing-in-Publication data: Salinity management handbook. Second edition Bibliography. Includes index. ISBN 0 7242 7412 X 1. Salinity—Control—Queensland. 2. Salinization—Control—Queensland. I. Queensland. Salinity and Contaminant Hydrology Group.
631.416
Landcare provided support for the publication of the first edition of this handbook
#28823
Re-printed 2011 with correction of minor factual and formatting errors. © The State of Queensland (Department of Environment and Resource Management) 2011
Department of Environment and Resource Management GPO Box 2454 Brisbane Qld 4001
If you need to access this document in a language other than English, please call the Translating and Interpreting Service (TIS National) on 131 450 and ask them to telephone Library Services on +61 7 3224 8412. This publication can be made available in alternative formats (including large print and audiotape) on request for people with a vision impairment. Contact (07) 322 48412 or email
ii Salinity management handbook Foreword
This handbook has been produced to address many The handbook aims to give a comprehensive set of of the questions by land managers and advisers about information to managers and advisers. It has a very understanding and managing salinity. Although practical focus providing direct advice on the most this form of land degradation is not widespread in commonly asked questions about salinity. It is divided Queensland, it causes great concern to those who into three main sections: understanding salinity, find it on their land. Many land managers are aware investigating salinity and managing salinity. of the impacts of salinity in southern Australia, and I commend this handbook to the reader. It provides are seeking to minimise or prevent similar impacts in an understanding of the basic principles of salinity, the north. and enables the reader to apply the processes to The handbook was compiled from information their particular regional situation. The investigation gathered through a series of regional salinity and management sections will assist landholders in workshops and investigations by Queensland research implementing the most appropriate management and and extension officers. It took into account, after reclamation practices to minimise the degradation of consultation and many joint projects, the ideas from land and water resources due to dryland and irrigation extension officers who were involved in providing salinity. advice on land development and land use options, This handbook will be a very useful reference manual and incorporated their feedback on the content for landholders, extension officers and research and format. It was given considerable impetus from officers, and is a valuable contribution to the national the demands to derive land clearing guidelines in effort being directed towards managing dryland Queensland in the early 1990s. salinity in Australia. While the handbook has a Queensland focus, it has developed broad principles and provides a process understanding that allows applicability to Adrian Webb a wide range of salinity situations. This approach Coordinator has particular value in allowing the selection of National Dryland Salinity Program investigation options ranging from simple ‘back of the envelope’ calculations to more sophisticated modelling options. Roger Shaw and Ian Gordon of the former Department of Natural Resources (now the Department of Environment and Resource Management) played a key role in collating and providing information and technical expertise for the production of this handbook.
Salinity management handbook iii iv Salinity management handbook Contents
Authors and contributors ix How to use this handbook x Answers to common questions about salinity xi Understanding salinity xi Investigating salinity xi Managing salinity xii Obtaining more advice xiv Abbreviations xv Units of measurement xvi
Part A — Understanding salinity 1
1 Salinity and sodicity______2 Types of salinity 2 Sources of salt 10 Environmental features contributing to salinity risk 11
2 Hydrologic controls on salinity______14 Groundwater movement model 14 Salt mass balance 17 Rate of water movement in the landscape 19
3 Salinity and hydrology management______22 Managing salinity by managing groundwater balance 22 Managing salinity by managing leaching fraction 22
Salinity management handbook v Part B — Investigating salinity 27
4 Features of salinity investigations______28 5 Measurement techniques and relationships______30 Electrical conductivity as a measure of salinity 30 Leaching fraction 32 Root zone salinity 34 Sodicity in soils and waters 37
6 Landscape characteristics and salinity mapping______39 Landform feature identification 39 Geology 42 Landscape salinity mapping 43 Landscape salinity hazard classification 48
7 Vegetation______49 Plant communities as salinity indicators 49 Vegetation patterns on remote sensing images 50 Plant response to salinity and specific ions 51
8 Climate and rainfall patterns______55 Average annual rainfall characteristics 55 Moving average rainfall pattern 56
9 Soils______58 Soil properties 58 Soil salinity 60 Soil salt profiles 61 Soil sodicity 63
10 Waters______65 Field tests for waters 65 Use of piezometers 66 Catchment groundwater balance estimation 70 Water chemistry and salt sources identification 73
vi Salinity management handbook 11 Water quality______79 Domestic use 79 Stock watering 79 Irrigation 81
12 Human activities______88 Human land use and records 88 Part C — Managing salinity 91
13 Management issues______92 Management options 92 Integrated management strategies 93 Management decision making 96
14 Vegetation management______98 Vegetation in areas of the landscape 98 General site treatment 100 Vegetation options 101 Pasture 102 Crops 103 Tree planting 104 Tree retention 107
15 Engineering methods ______110 Drainage 110 Groundwater pumping 111
16 Irrigation management______115 Irrigation management to minimise watertable rise 115 Marginal quality irrigation waters 116
Salinity management handbook vii Appendixes
1 Landscape features diagnostic chart______120 2 Plant salt-tolerance data ______124 3 Pasture species for saline soils ______133 4 Tree species for salinity management______137 5 Useful software packages______141 6 Salinity publications for further reference______145
References 152 Useful conversions and relationships 158 Glossary 161 Index 165
viii Salinity management handbook Authors and contributors
This handbook was compiled from information Eve Witney, a technical writer with qualifications gathered during a series of regional salinity in environmental science and in communication, workshops, organised by the then Queensland compiled and rewrote available salinity information Department of Primary Industries (DPI) from 1985 to into the current format, and obtained further 1987 (previously published in the DPI Conference information as required. The publication was designed and Workshop Series), augmented by subsequent and desktopped by Melissa Whyte and produced by investigations by DPI research and extension officers Scientific Publishing, Resource Sciences Centre. with the (then) Salinity and Contaminant Hydrology Acknowledgment and appreciation is extended group (SalCon), now part of the Department of to other staff of the former Department of Natural Environment and Resource Management and the Resources, Department of Primary Industries, Department of Employment, Economic Development Department of Environment and Heritage, landcare and Innovation. representatives and landholders. People who Roger Shaw and Ian Gordon, scientists with the provided comment on initial drafts of this handbook Resource Sciences Centre, provided the substantive include Bob Baldwin, Geoff Bass, George Bourne, Jon material which forms the basis of this handbook, Burgess, David Carberry, John Chamberlain, David and provided primary technical expertise throughout Dempster, Terry Donnollan, Geoff Falkner, Trevor the period of the handbook’s development. David Glanville, James Gourley, Keryn Hunt, Clive Knowles- Hinchley, of the former DPI Forestry, compiled and Jackson, Cindy Lamb, Bruce Lawrie, Jim McClurg, provided material relating to the use of vegetation, Yvonne Orlando, Geoff Paton, Ernie Rider, Max in particular trees, to manage salting. Further Roberts, Russ Scarborough, Phil Sorby, Leath Stewart, technical expertise was contributed by Clem Hill, Frank Sunners, Meryl Thomas and Geoff Titmarsh. Peter Thorburn, Lindsay Brebber, John Doherty, Ingrid Christiansen, Adrian Stallman, Geoff Carlin, Tony Dowling and Keith Hughes.
Salinity management handbook ix How to use this handbook
This handbook, based largely on work in north-eastern In Managing salinity, the major management aspects Australia, provides a comprehensive and practical of vegetation, irrigation and engineering applications introduction to salinity by: are discussed individually and in relation to each • understanding salinity processes other. The process of developing an integrated management strategy that addresses the nature of • investigating the risk of salinity in a landscape and local salinity processes and the extent of current determining the extent of current salting salting as well as the interests of the landholder and • developing an integrated salinity management other stakeholders is considered. strategy The Appendixes contain tables and charts of useful • locating additional detailed information. information: In Understanding salinity, the three major types • tree and pasture species suitable for saline or of salting are described. Most salting outbreaks waterlogged conditions result from imbalances in the hydrologic system of a • salt tolerance data for more than 130 plant species landscape. Certain landscapes are more vulnerable to salting than others, and the major contributing • a diagnostic chart for identifying landscape features factors of climate (particularly rainfall patterns), at risk of salinity geomorphic features (landscape characteristics and • software packages for analysing salinity processes underlying geology) and human activity are discussed. and developing salinity management strategies Sustainable strategies for managing salinity rely on • sources of salinity information for further research addressing imbalances in the hydrologic system. and reference In Investigating salinity, practical information for • salinity investigations carried out in Queensland planning and carrying out salinity investigations is since the early 1970s. provided. By looking at geomorphic features, climate In Useful conversions and relationships, equations and land use, it is possible to assess whether an area and charts for converting EC units, measures of is at risk of salting, either currently or under changed salinity, units of concentration, SAR and ESP, and conditions. If salting is currently suspected, detailed measures of soil volume and density are provided. investigations looking at indicator plant species and soil and water data will reveal the extent of salting and the processes contributing to the problem.
x Salinity management handbook Answers to common questions about salinity
This handbook is designed to address land managers’ balance is covered in Catchment groundwater balance and advisers’ questions about understanding, estimation (page 70). This information, together with investigating and managing salinity. Common soil salinity data, allows us to assess the extent and questions about salinity are addressed in this section, severity of a salinity problem. with guides to the sections of the handbook where the What do I need to know to assess salinity hazard? issues raised are discussed more fully. What factors make up a salinity investigation? Because salinity is the result of the complex Understanding salinity interaction of geophysical and land use factors, salinity investigations need to address a range of Why is salinity occurring in this area and not in issues to identify the risk of salinity or the likely extent others? of possible salinity problems. Information about What factors have contributed to this salinity current and potential salinity levels and processes can problem? be determined from: Whether and how salinity becomes evident at a • landform features and geology in the catchment particular location depends on the interaction of many • vegetation species and communities, and specific factors—characteristics of the landscape itself, the responses to salinity or ion toxicity climate and the effects of human activities are the most important. An understanding of the hydrology of • local climate and long-term rainfall patterns the salt-affected area is needed to determine the likely • soil properties, salinity and sodicity levels extent of any problem. Understanding salinity (page 1) • water characteristics, salinity and sodicity levels deals with the range of factors contributing to salinity • land use records. in general as well as at specific locations. Investigation components are listed in the table Why are my crop returns less each year? Features of salinity investigations (page 28), along Why are different species growing in pasture areas? with the type of information each can contribute to a Crop yields can be affected by salinity and/or salinity investigation. waterlogging problems which may not be evident on Is it possible to undertake a simple, initial the soil surface. In pasture areas, a change in species investigation to determine whether a more detailed composition may indicate increased levels of soil investigation is necessary? salinity. Soil sampling to measure salinity (EC) is required to check whether in fact it is salinity that is Yes. An initial assessment of current salinity and causing these effects. Refer to the section Soil salinity salinity potential can be undertaken at very low cost. (page 60) for information on taking field EC measures, A lot can be determined about the current extent of and the appendix Plant salt tolerance data (page 124) salting by considering a few observable or readily for information on the relative salt tolerance of many measurable factors and using available information. plant species. The features to consider are: • electrical conductivity of surface waters and accessible groundwater points Investigating salinity • depth to the groundwater in existing bores How ‘bad’ is this salinity problem? • catchment shape and landscape features Is it likely to get worse? • average annual rainfall and seasonality Investigating salinity (page 27) provides strategies for • vegetation—composition and vigour of crops, investigating and determining the nature of salinity pasture and native species at a particular location. Salinity problems often result • current land use, and history of land use from excess water which, as it evaporates, deposits the salts that have been dissolved in the water. This • field soil electrical conductivity. water is potentially a valuable resource that could be Once the likely risk area can be pinpointed from an utilised on-farm. A simple catchment water balance initial investigation, the consequences for the area calculation can be used to identify the amount of and the catchment need to be assessed. The scale of excess water that needs to be removed to alleviate the subsequent investigation needs to be tailored to the salinity problem. Calculating catchment water the available range of management options.
Salinity management handbook xi Detailed information on salinity investigation What are the water quality requirements for irrigation? strategies is provided in Investigating salinity Can I predict how irrigation water use will affect soil (page 27). properties over time? Can I look for particular plant species that indicate Irrigation water quality criteria depend on soil salinity? properties, climate, plant species and management practices. Water composition alone will provide only Within a particular biogeographical zone, certain a general guide for average conditions, and may grass, shrub and tree species will have adapted to provide inadequate information for local conditions. waterlogged and/or saline conditions. The presence The recommended approach is to assess water of these species, in combination with other factors, quality parameters in conjunction with soil properties can indicate salinity problems (both existing and (particularly leaching). Leaching is the critical property potential). These species and the other factors to of a soil that must be considered when predicting how be considered are covered in Plant communities as a particular soil will respond to a particular irrigation salinity indicators (page 49). water. The interaction of soil salinity and the sodium Can I identify an area that has the potential to develop adsorption ratio of the soil water (SAR) will determine salinity? What if initial investigations indicate such how leaching will be affected by the irrigation water. sites, but current salinity levels aren’t affecting land Several relationships have been developed that will use? allow changes in SAR and soil salinity to be predicted Because salinity develops due to the interaction over time. These and other issues are addressed in between salt sources, landscape characteristics Irrigation (page 81). and human activity, it is possible to identify which What are the water quality requirements for human combinations of features will make a catchment, and stock use? or specific sites within a catchment, more sensitive Criteria for assessing the quality of water for human to salinity. Criteria for identifying and classifying and stock use have been developed by ANZECC areas that may be prone to salting are presented in (1992, currently being revised). A summary of this Guidelines for retaining trees (page 107). If salinity information is provided in Water quality (page 79). has not yet occurred, it would be wise to assess possible risk and monitor current salinity development before undertaking works or developments which Managing salinity will affect the hydrologic balance of the landscape, such as clearing vegetation, building dams, irrigating How can we develop an integrated management or subdividing rural land. Monitoring would involve strategy that best addresses the landholder’s needs, periodic soil profile analyses and checking watertable the type and extent of salinity, and the available levels in existing bores or specially installed options? piezometers. After all, prevention is much more The best way to develop a strategy with the greatest cost-effective than reclamation. likelihood of success is to comprehensively Can the effect of salinity on plant productivity be investigate the processes and severity of salinity predicted? in the area, and then to develop a plan which incorporates whole-of-catchment processes and Some plant species are better adapted for coping with whole-of-farm activities. Management options salinity than others. Most studies on the salt tolerance include revegetating (with crops, pastures or trees) of plant species have been conducted in laboratories. or retaining existing vegetation, installing drainage However, plant salt tolerance in any field situation will or pumps as engineering solutions, and possibly depend on the interaction of a number of factors not irrigating with the excess groundwater. These issues readily accounted for in laboratory experiments, such are discussed comprehensively in Management as stage of growth, management practices, climate issues (page 92). and fertility levels. Two measures of salinity in the root zone have been derived which enable plant response How much will it cost to manage salinity? to be predicted under field conditions.Plant response What can be done cheaply? to salinity and specific ions (page 51) looks at how The cost of salinity management will depend on the plants cope with salinity, factors which affect plants’ processes contributing to the problem (and hence ability to cope, and measures of salinity in the root the viable management options), combined with the zone which can be used to predict plant response. choice of options that are most compatible with the land owner’s goals. Options range from ‘fence and forget’ (for the cost of fencing combined with the loss of productivity from that site, balanced against potential future losses for not taking this action) to extensive tree planting on recharge areas or engineering works. xii Salinity management handbook How long will it take for salinity management What species of plants—trees, crops or pastures—can strategies to work? What do I look for to tell if the I plant, and where should I plant them? management is working? If planting vegetation is a viable option for managing Changes in the hydrology of a catchment can result in salinity or waterlogging, information on plant salt salinity problems that may not manifest for 30 to 50 tolerance and soil and water salinity can be used years. However, once a problem arises, it will be much to select appropriate species for the prevailing more difficult to manage, and sub-critical conditions conditions. Tree planting is a long-term and potentially may reduce productivity for years before the problem expensive option for managing salinity. However, tree becomes readily apparent. Preventative management planting provides many opportunities for diversifying in sensitive catchments is highly recommended. farm income with the production of timber, farm wood, fuel wood, honey, oils or seeds. Trees provide Just as salinity problems can take 30 to 50 years additional benefits for existing farm activities, such to develop, so it may take a similar time frame for as providing windbreaks and shade, shelter and saline sites to be reclaimed, particularly if pursuing potential forage for stock. These issues and points on vegetation options for management. However, establishing and maintaining trees planted for salinity engineering options could be successful in alleviating management are discussed in Tree planting (page problems in just a few years. To check on the effects 106). A detailed listing of trees suitable for salinity of salinity management, monitoring the depth of the management, tolerances and potential multiple uses groundwater, quality of the groundwater, and soil are provided in the appendix Tree species for salinity salinity are most important. Within a framework of management (page 137). property management planning and utilising the range of decision support resources available, the effect of A comprehensive listing of crops with information on management strategies on the land and on property salinity tolerance is provided in the appendix Plant operations can be charted. salt tolerance data (page 124). Information on growing crops in salted catchments is provided in Crops (page What is the best use for this land? Should I stick with 103). crops, or should I go to pasture or plant trees? Which is best for controlling salinity? Salt-tolerant pasture species suitable for Queensland conditions are listed and discussed in the appendix Vegetation can be used in recharge, transmission and Pasture species for saline soils (page 133). Other discharge areas to manage salinity in the catchment information on the salt tolerance of various plant depending on water use needs, local conditions species is provided in the appendix Plant salt and the landholder’s farm management strategy. It tolerance data (page 124). In Pasture (page 102), is most important that any vegetation strategy uses issues in establishing and maintaining pasture are species which are well suited to the site conditions considered. to improve the chances of survival and good growth under potentially unfavourable conditions. Refer to What type of drainage works or other engineering Vegetation management (page 98) for discussion on options would best suit these conditions? selecting the most appropriate vegetation strategy as Engineering options include surface and subsurface well as information on establishing and maintaining drainage and groundwater pumping. These options pasture, crops and trees. have specific application in a limited number of Where should I clear trees, and how many can I clear, situations, and can best be used to manage salinity in to minimise the likelihood of salinity developing? conjunction with other management practices. When incorporating any engineering option, the responsible In vulnerable landscapes, salinity can become disposal of drainage effluent must be considered. apparent from 20 to 50 years after vegetation is These issues, and techniques for designing and cleared. This is not to say that all tree clearing in installing engineering options, are discussed in vulnerable landscapes results in salinity. Clearing Engineering methods (page 110). The type and design can be planned to make land available for alternative of any drainage scheme implemented to manage land uses as well as minimising the risk of salinity salinity or waterlogging at a particular location will developing. This will depend on the results of local depend on soil properties, aquifer properties and salinity investigations. The section Tree retention disposal options. Information on selecting and (page 107) provides information on identifying areas designing drainage works is provided in Drainage at risk from salinity and recommends strategies for (page 110). Drainage effluent (wastewater) must be tree retention. disposed of in a way that does not impact on water quality downstream. Depending on water quality, options range from fully constrained disposal basins to dilution or reuse (as discussed in Drainage water disposal page 110).
Salinity management handbook xiii Can I use groundwater to irrigate? Obtaining more advice How can I best manage irrigating with this water? Where in Queensland has salinity been investigated, If groundwater is of good or marginal quality, it can and what was found? How was it dealt with? be used to irrigate existing or proposed crops, trees or pastures on the property. Irrigation needs to be Many of the numerous papers and reports that have managed to avoid watertable rise and control the been compiled on salinity in Queensland are listed, build-up of salinity or sodicity in the irrigated soils. by locality, in the appendix Salinity publications for Specific practices are recommended for irrigating futher reference (page 145). with marginal quality saline and sodic waters. Water What reference materials will help me with my quality criteria and likely impacts of irrigation water on investigations and decision making? soils and plants are discussed in Irrigation (page 81), A list of recommended reading material for further and strategies for irrigating effectively are outlined in information on salinity and related topics is provided Irrigation management (page 115). in the appendix Salinity publications for further reference (page 145). Where can I get more advice and assistance? For advice or assistance on salinity-related issues, contact DERM or DEEDI or visit the DERM website:
xiv Salinity management handbook Abbreviations
A area, either surface area or LF leaching fraction cross-section of a vertical face as specified LR leaching requirement ADMC air dry soil moisture content PLF predicted leaching fraction AHD Australian height datum Q quantity of water ARZS average root zone salinity RA residual alkali (sodium carbonate plus bicarbonate) BD bulk density S surface seepage rate CCR CEC to clay content ratio SAR sodium adsorption ratio CEC cation exchange capacity SP saturation percentage Dd deep drainage below the root zone T transmissivity of an aquifer E evaporation rate TDI total dissolved ions EC electrical conductivity TDS total dissolved solids EC1:5 electrical conductivity of 1:5 TSS total soluble salts soil water suspension Wmax maximum field water content, measured or predicted from EC1:5 /ECCl ratio of EC1:5 to EC due to Cl in 1:5 soil water suspension relationships of Shaw and Yule (1978); Wmax is a measure ECs electrical conductivity at water of ‘field capacity’ which is content approximating field more appropriate for swelling capacity clay soils than laboratory techniques ECse electrical conductivity of soil saturation extract WF weighting factor for soil depth increment ESP exchangeable sodium percentage WUW water uptake weighted, usually applied to root zone salinity or ET evapotranspiration rate leaching fraction ∆H hydraulic gradient Y plant (crop) yield K hydraulic conductivity of a z depth of root zone porous medium Ks saturated soil hydraulic conductivity
Salinity management handbook xv Units of measurement
Quantity Symbol Unit Equivalence in base units Length m metre cm centimetre 10–2m mm millimetre 10–3m
Area m2 square metre ha hectare 104m2
Time s second d day yr year myr million years
Temperature °C degrees Celsius
Mass kg kilogram g gram 10–3kg mg milligram 10–6kg t tonne 103kg
Volume m3 cubic metre L litre 10–3m3 ML megalitre 103m3
Concentration mmole/L millimoles/litre 10–3mole/L mmolec/L millimoles (charge) per litre meq/L millequivalent per litre mg/kg milligrams per kilogram ppm parts per million
Electrical conductivity dS/m decisiemens/metre mS/m millisiemens/metre 10–2 dS/m µS/m microsiemens/metre S/m siemens/metre
Pressure/suction kPa kilopascal 103 Pa
xvi Salinity management handbook Part A — Understanding
1 Salinity and sodicity
2 Hydrologic controls on salinity
3 Salinity and hydrology management
Salinity management handbook 1 Chapter 1 — Salinity and sodicity
Salinity is the presence of soluble salts in soils or sodium attached to clay mineral exchange sites waters. Salinity processes are natural processes weakens the bonds between soil particles when the closely linked with landscape and soil formation soil is wetted. As a result, the clay particles swell and processes. However, human activities can accelerate often become detached and disperse. The small clay salinity processes, contributing to long-term land and particles move through the soil, clogging the pore water degradation. Salinity usually becomes a land spaces. use issue when the concentration of salt or sodium Sodicity is a condition that degrades soil properties adversely affects plant growth (crops, pastures by making the soil more dispersible, restricting water or native vegetation) or degrades soil structure. It entry and reducing hydraulic conductivity (the ability becomes a water issue when the potential use of a of the soil to conduct water). These factors limit water is limited by its salt content. leaching so that salt accumulates over long periods Salt is derived from the weathering of the earth’s crust of time, giving rise to saline subsoils. A soil with and is transported and deposited in the landscape by increased dispersibility becomes more susceptible to hydrologic mechanisms (rainfall and water movement erosion by water and wind. above and below the terrestrial surface). Although Sodic soils become dense, cloddy and structureless the salt content of rainfall is low, rainfall can be the on drying because natural aggregation is destroyed. dominant source of salt in some areas. Over millennia, The dispersed clay at the soil surface can act as salt has accumulated in areas where water drainage a cement, forming crusts that are relatively dense has been very slow, or where shallow watertables and hard but typically thin (up to 10 mm thick). The occurred during wetter geologic periods. crust impedes seedling emergence and can tear Because land uses such as agriculture disturb the seedling roots as it dries and shrinks. The degree of natural hydrologic equilibrium in a landscape, salinity crusting depends on the soil textural composition, processes are also affected. Human activities in the mineralogy of the clay, the exchangeable sodium developing land and water resources can change content, the energy of raindrop impact, and the rate of the hydrologic equilibrium in sensitive areas. Salt drying. Soils with high montmorillonite clay contents problems in agriculture are not new; the decline will crack on drying. of civilisations in ancient Mesopotamia has been The genesis of some soils has resulted in sodic associated with soil salting under irrigation with rising subsoils, often with a columnar structure. Sodic saline watertables (Jacobsen & Adams 1958). subsoils may be dense, with reduced soil water Salinity usually develops gradually over an extended storage, poor aeration and increased soil strength, period of time. Often, landholders become aware of and can be susceptible to tunnel erosion. salinity on their land only after observing a gradual Sodic soils occur naturally in Queensland. Sodicity loss of productivity over a number of years. can also be associated with irrigation water salting Although salinity can cause production losses, (page 82) or erosion scalding (page 9). In this seasonal variability in factors such as rainfall, handbook, the term ‘salinity’, when used to describe temperature, solar radiation and incidence of pests salinity issues in general, usually encompasses and diseases have a much greater effect on yields sodicity as well. than salinity in the short term. However, salinity can be an important issue for individual landholders depending on the position of their property in the Types of salinity catchment because substantial proportions of Primary salinity is salinity that occurs naturally in individual properties can be affected. soils and waters. Secondary salinity refers to salting Sodicity in soil or water is defined as the presence that results from human activities, usually land of a high proportion of sodium ions relative to other development and agriculture. (Salting, also called cations (in exchangeable and/or soluble form). As salinisation, is the process and result of soluble salts sodium salts, such as sodium chloride (NaCl), are accumulating in soils or waters.) leached through the soil, some sodium remains in the The division between primary and secondary salinity soil bound to clay particles, displacing other cations is useful for separating areas where human activities such as calcium. A high proportion of exchangeable
2 Salinity management handbook do not appear to be affecting salinity processes Figure 2. Diagrammatic representation of processes (primary salinity) from areas where salinity is clearly contributing to dryland salinity. influenced by human activities (secondary salinity), frequently associated with quite rapid changes in the environment. However, it is often difficult to categorise salting outbreaks as one or the other type because secondary salinity is often primary salinity rain accelerated by human activity. Many areas that now exhibit secondary salinity show considerable evidence transpiration annual pastures of having been affected by primary salinity in the past. transpiration Primary salinity appears as naturally occurring saline areas and saline soils. Salt lakes, salt pans, salt evaporation marshes and salt flats are all examples of naturally occurring saline areas (Figure 1). Secondary salinity can be divided into three groups salt-affected area on the basis of the processes contributing to salting watertable (Figure 2): • Watertable salting is a concentration of salts associated with evaporation of water from a artesian bore shallow watertable (that is, the upper surface of the recharge through fallow fields recharge through fractures groundwater). This process contributes to salinity in both irrigated and dryland (non-irrigated) areas. Seepage salting is a type of watertable salting that occurs when groundwater seeps at the ground Naturally occurring saline and sodic surface. soils Figure 1. Examples of saline areas which occur naturally. The distribution of naturally occurring saline soils in Australia is closely related to the occurrence of geomorphic basins with closed drainage and low hydraulic gradients. About 5.3% of the land area of
non-saline soils Australia is naturally saline (Northcote & Skene 1972). Saline soils occur naturally in Queensland in the salt flat south-west, associated with springs of Great Artesian saline subsoils sea level natural level watertable salt pan Basin waters, and in very flat areas around the coast, shallow watertable salt marsh such as in the Gulf of Carpentaria around Normanton watertable at soil surface (Figure 3). In 1972, approximately 0.35% of the total land area of Queensland was estimated to be affected by naturally occurring saline soils (Northcote & Skene • Irrigation water salting is salting associated with 1972). the accumulation of salts from irrigation water in the soil and the effect of the water composition Although factors such as reduced accessions of on soil properties. The sodicity of irrigation water sodium in rainfall in northern latitudes (see Climate and the properties of irrigated soils are important and rainfall patterns page 55) would suggest that components of irrigation water salting. Queensland would have less sodic soils than southern • Erosion scalding is salting primarily caused by Australian States, the relative proportion of sodic soils erosion processes. This occurs when surface soils in Queensland is in fact similar to that in other States are eroded by surface water flow or wind, exposing (Northcote & Skene 1972). This is largely because past saline and/or sodic subsoils. soil forming processes appear to have dominated sodic soil formation. This handbook will deal mostly with the first two types of secondary salinity, watertable salting and irrigation On an area basis (Figure 5), 55% of Queensland soils water salting, and with sodicity. are described as non-sodic, 24% as strongly sodic, 1% as sodic, and 20% as having variable sodicity in the root zone (Shaw et al. 1994).
Salinity management handbook 3 Figure 3. Distribution of naturally occurring saline soils in Queensland (Northcote & Skene 1972). Used with permission from CSIRO.
Cairns
Normanton
To wnsville
saline soils Mount Isa saline areas
Rockhampton
Charleville
Brisbane
Figure 4. Natural groundwater discharge of the Great Artesian Basin associated with geological faulting which has formed mound springs in the South Australian section of the basin.
4 Salinity management handbook Figure 5. Distribution of naturally occurring sodic soils in Queensland (Shaw et al. 1994). Used with permission from CSIRO.
Cairns
soil sodicity sodic To wnsville strongly sodic variable
Mount Isa non-sodic
Rockhampton
Charleville
Brisbane
Figure 6. Naturally occurring sodic subsoils.
Salinity management handbook 5 Watertable salting Watertable salting can occur in irrigated areas as well as dryland areas. When groundwaters are used Appearance for irrigation, watertable rise is rarely a problem because there is no net increase in the amount of Salting associated with a rising or shallow watertable water entering the catchment; excess water draining can become apparent in the following ways: below the root zone is effectively cycled from the • The ground surface may become permanently groundwater to the irrigation water and back to the or seasonally damp or waterlogged, or remain groundwater (Figure 7). Watertable rise is more likely damp for extended periods after rain. Previously to occur when surface waters are used for irrigation ephemeral gullies and streamlines may begin to because this increases the water inputs to the flow continuously or for longer periods. system—amounting to a 200 to 600 mm/yr effective • Vegetation in low-lying areas may fail to germinate increase in rainfall, doubling rainfall input in some or grow, or may die off over a period of time. irrigation areas. • Pasture composition and diversity may change In dryland areas, watertable salting usually over time so that couch grass or other salt-tolerant occurs after vegetation clearing and subsequent species dominate. development reduces water use and thus the ability of • In residential areas, buildings may suffer from the system to maintain the watertable at an adequate rising damp. depth below the soil surface.
• Groundwater quality may deteriorate. Figure 7. Groundwater irrigation cycles water within An area severely affected by watertable salting the system, but irrigation with surface water increases typically consists of a bare area, perhaps with a water inputs to the system, increasing the likelihood of watertable rise. salt-encrusted soil surface, fringed by salt-tolerant vegetation, with groundwater underlying or seeping water pumped from aquifer through the soil surface. In a seepage area, the ground will appear wet or shiny. If the salting is not severe, the seepage area itself may be lightly vegetated with salt- and water-tolerant species but the surrounding area may be bare. In some situations, the groundwater does not rise near the soil surface because a deep creek or gully in the vicinity intersects the watertable watertable equilibrium and acts as a drain. The base flow in such a drain may be poor quality, saline water.
aquifer Process Watertable salting (discussed in detail in Hydrologic controls on salinity page 14) occurs when the watertable exists close to the soil surface. Capillary action draws water from the watertable upwards Occurrence in Queensland through the soil. This water evaporates or is used by In 1990, the Department of Primary Industries vegetation. Salts which were dissolved in the water conducted a survey of available information on lands accumulate at the soil surface or in the root zone affected by and susceptible to secondary watertable when the water is removed. Salt concentration can salting (Gordon 1991). Reports of salt-affected land increase to a level at which vegetation can no longer were concentrated in the south-east, south and survive. central Queensland regions, and were commonly Seepage salting, a form of watertable salting, associated with basalt areas that receive an average occurs when the watertable is at the soil surface, of 500 to 1 200 mm of rainfall each year. Watertable permanently or seasonally, and groundwater seeps salting was found to seriously affect 10 000 ha of through the soil surface. A seepage can reduce land in Queensland; at least a further 73 000 ha was salt accumulation in the soil by moving salt to the identified as being susceptible to salting. Areas of soil surface and flushing it away. However, salt can known salinity in 1990 are indicated on Figure 8. New accumulate in the area surrounding a seepage as a outbreaks have occurred since that time. result of capillary action from the shallow watertable. Where watertable salting occurs, the groundwater itself is often, but not necessarily, saline.
6 Salinity management handbook Figure 8. Known areas of land severely affected by salinity in Queensland in 1990 (Gordon 1991).
known salinity areas salinity areas
Figure 9. Soil salinity effects on irrigated cotton due to evaporation from shallow groundwater in the Emerald Irrigation Area, Queensland. The problem was reclaimed with the installation of shallow drainage.
Salinity management handbook 7 The affected area was greater than that reported in an • Leaching moves salt below the root zone. Under earlier study (Hughes 1979, updated in 1982), which certain soil conditions or water management described 7 900 ha of salt-affected land. The overall practices, and where sodicity is a problem, leaching trend is for an increase in the number of salt-affected rates may not be sufficient to maintain salt in the areas in Queensland. The extent of affected areas root zone below a concentration at which plant fluctuates seasonally, and sharp increases in area productivity is affected. often occur following very wet years. Under irrigation, salts leached from the root zone The area under irrigation affected by rising watertables tend to move downwards into the groundwater. in Queensland is small. Watertable salting has been In groundwater irrigation schemes, the salt recorded in the Emerald, Maryborough, Mareeba– concentration of the groundwater supply may Dimbulah, Bundaberg, and Burdekin irrigation areas increase, contributing greater amounts of salt to the where approximately 400 ha of land is seriously soil over long time periods (decades). affected (Gordon 1991). An increasing problem in Irrigation water salting can be partly controlled the Emerald Irrigation Area has been controlled by by growing salt-tolerant crops and by fine-tuning subsurface drainage. One reason for the low incidence irrigation management. Where irrigation is used only of watertable salting in Queensland irrigation areas to supplement rainfall, salinity is of less concern than compared with irrigation areas in southern States is sodicity; the soil salt concentration can be reduced that a greater proportion of Queensland irrigation is dramatically by wet season rainfall but the proportion based on groundwater supplies. of sodium ions in the soil will remain high or increase slightly. Irrigation water salting Occurrence in Queensland Appearance It is difficult to assess the area of soils that are In irrigated areas, the effect of irrigation water quality affected by salt from the use of marginal quality on soil behaviour and plant growth may be apparent irrigation waters. The system tends to be self- as: regulating: growers match crops to water and soil • Crop yields may decline progressively over a characteristics; when it is no longer possible to grow number of years or be significantly reduced in dry certain irrigated crops productively, irrigation is years. stopped or other crops are grown. • In severely affected areas, soils may appear ‘fluffy’ In Queensland, 36% of the irrigation water used and light (characteristic of saline soils). The soil is groundwater (Australian Bureau of Statistics surface may be dispersible, water infiltration 1993). Groundwaters in most major groundwater- limited, the seedbed poor, and germination poor or based irrigation areas in Queensland are suitable unsuccessful (characteristic of sodic soils). for irrigating a wide range of salt-sensitive and • Crops may appear water-stressed even though mildly salt-sensitive plants, except in the Lockyer adequate amounts of water have been applied. Valley and Dee River where 34% and 64% of waters respectively are suitable only for irrigating plants Process with higher salt tolerances. In Table 1, waters in a number of Queensland groundwater irrigation areas Irrigation water salting and sodicity occur when salts are classified according to the salinity hazard that the (including sodium) from irrigation waters accumulate groundwater poses for plants. in soils. This is caused by the two interacting processes of salt accumulation and insufficient leaching: • All natural waters contain salt. Salt from irrigation waters accumulates in irrigated soils as the water is removed by evaporation and transpiration. Poor quality irrigation waters contribute comparatively greater amounts of salt.
8 Salinity management handbook Table 1. Relative salinity hazard of groundwaters from some This crust inhibits vegetation growth, increases runoff groundwater irrigation areas in Queensland (adapted from and contributes to poor soil structure. The dispersed Shaw et al. 1987; plant salt tolerance groupings based on surface is made up of (mostly fine) sand, silt and the criteria of Maas & Hoffman 1977). enough sodic clay to cement it together when dry and % of waters in each region falling within the seal the surface. The crust disperses when wet. Region plant salt tolerance grouping low medium high very high extreme Occurrence in Queensland
Lockyer Valley 10 56 21 13 >1 Approximately 590 000 ha of land in Queensland are Bundaberg affected to some degree by erosion scalding (Working 58 40 2 0 0 Irrigation Area Party on Dryland Salinity 1982). Scalding is most Callide Valley 42 36 14 6 2 common in Queensland on heavily grazed, fragile Dee River 2 32 42 22 2 soils in the arid and semiarid regions in the west of the State (rainfall less than 500 mm per annum). Burdekin Delta 100 0 0 0 0 Queensland* 34 27 17 10 12 Figure 10. Erosion occurring on an extensive scalded area of exposed sodic subsoil in south-west Queensland. Note: *The data for Queensland are an average of the analyses of samples during the period 1988–93 (R. de Hayr, pers. comm.). The samples included irrigation waters suspected of causing problems as well as waters from new bores.
Erosion scalding
Appearance Areas affected by erosion in conjunction with high salinity or sodicity may appear as follows: • Midslope and flat areas may become bare of vegetation or support only stunted vegetation growth. • The soil surface in some areas may be hard and compacted when dry or eroded. • Pasture composition may change and diversity decrease over time. Figure 11. Historic salt deposits in an area adjacent to the In general, the ground in a scald will be bare or may be Dead Sea, Israel. partially covered by drought- or salt-tolerant species or stunted vegetation. Usually, the soil surface will appear hard and compacted. If stones are present in the subsoil, the eroded surface may have a stone- packed appearance. If the subsoils are strongly saline, salt crystals may be apparent on the soil surface. High subsoil sodicity is a dominant features of scalds. Areas surrounding scalds can also be affected by the process contributing to the scalding—that is, erosion and deposition of eroded material.
Process The process of scalding usually begins when vegetation is removed—whether by clearing or overgrazing or by drought or fire. Without vegetation to bind the soil and provide a protective cover, wind and water erosion remove the topsoil, exposing the subsoil. A dispersed surface (crust) forms on the surface of the subsoil.
Salinity management handbook 9 Figure 12. Chloride concentration in rainfall with distance Sources of salt from the coast for two latitude ranges (plotted from the The dominant sources of salt are rainfall and rock data of Isbell et al. 1983 from Shaw et al. 1994). Used with weathering. Rain is a dilute source of salt, but over permission from CSIRO. time, salt deposited by rain can accumulate in the 1 landscape. Rainfall contributes salt to the landscape at about two to three times the ‘average’ rate that weathering contributes salt, based on some broad estimates (Shaw et al. 1987). However, weathering 0.2 /L)
can be a dominant source of salt in some landscapes, c particularly in Queensland. The dominant source of salts in a particular area will depend on the rock types 0.1 and the extent of weathering. Rainfall patterns and soil properties determine the extent to which weathering products remain in the soil 0.02 profile. In areas with high rainfall and good drainage o o chloride concentration (mmole latitude 30 to 40 S (such as the wet tropical and subtropical coast of latitude 18o to 24oS Queensland), most of the salt produced by weathering 0.01 is flushed out of the landscape. The converse is true, and particularly so, in more arid areas where rainfall is insufficient to leach salt and where drainage out of the 0 10 1001 000 region is restricted, such as in Lake Eyre. distance from the coast (km) Where rainfall is the dominant source of salt, sodium Queensland has a low incidence of marine sediments chloride is the most common salt. Where weathering compared with other Australian States. Extensive dominates, bicarbonate salts are more common. marine inundation occurred in Victoria during the late Mesozoic to early Cainozoic (approximately 135 to 50 Rainfall million years ago). These marine sediments, in areas The concentration of salt in rainfall is greatest near such as the Murray Basin, are a primary source of the coast, and decreases inland as distance from salt (Macumber 1978; Evans et al. 1990). In contrast, the coast increases. Salt accessions from rainfall are Queensland has had little marine inundation since greater in southern latitudes than in northern latitudes the Mesozoic and none since the early Cainozoic (Figure 12). For instance, the salt concentration of (approximately 65 million years ago) (Beckmann rainfall near the coast north of 24°S (say, Gladstone) 1983). is about one-tenth of the concentration of salt in Igneous rocks generally have low chloride contents. rainfall near the coast in latitudes south of 30°S (say, The relative distribution of volcanic areas in Grafton). Queensland is similar to other eastern states, but Differences in sea surface salinity combined with wind the Queensland occurrences are of a greater age. patterns and intensities may explain this latitude Volcanic areas in Queensland are intensively used effect. Variations in sea surface salinities, which for agriculture and have a lower incidence of sodic depend on relative precipitation and evaporation soils than other parts of the state. This is due to the rates, are minor in Australian oceanic regions (less dominance of calcium and magnesium over sodium in than 2 000 mg/L) (Shaw et al. 1994). the parent rock material. The chemical composition of salts in aquifers can Weathering be used to determine the types of rocks contributing salts to the groundwater and to trace the movement All weathered rock types contribute salts to the of water through the landscape. The aquifers landscape to differing extents. For instance, marine contributing water to salted areas in Queensland sediments contain greater amounts of salt than tend to be considerably less saline than in other freshwater sediments, and contribute more salt on states. Whereas the salts in most southern states are weathering. The texture of sediments influences the dominantly sodium chloride (NaCl), in Queensland extent to which salt is retained during weathering. magnesium (Mg) can be the dominant or co-dominant The salts derived from marine sediments are mainly cation, particularly in basalt (igneous) areas. sodium and magnesium chlorides. Bicarbonate (HCO3-) levels are often much higher in Queensland than in southern states; in some
10 Salinity management handbook areas it is the dominant anion, indicating active rock compatible with soil infiltration rates. These factors weathering rather than a particular geology. However, result in a net water surplus so that water moves the relative concentrations of salts in aquifers will below the root zone to the watertable. (This process change over long time periods under the is discussed further in Hydrologic controls on salinity influence of local chemical processes (seeWater page 14). This also results in greater leaching of salts chemistry and salt sources identification page 73.) into the groundwater (Yaalon 1983). In contrast, summer-dominant rainfall occurs during Aeolian deposits the active growth period when plant demand and evaporation rates are both high. Summer rainfall is Wind-transported (aeolian) materials from soil or lake usually of higher intensity with proportionally greater surfaces are another source of salt. (This process has runoff. As a result, a much smaller proportion of been described by Bowler 1990.) However, airborne water moves below the root zone as deep drainage redistribution is a comparatively small source of salt than in winter-rainfall areas, reducing the likelihood in Queensland because of the general absence of of watertable rise. In some areas in subtropical saline soils, except in the south-west corner, and lack and tropical coastal Queensland, rainfall exceeds of current or historic saline lakes or soils in this State evapotranspiration due to the volume of rainfall compared with Victoria and Western Australia. during the wet season. Water balance modelling for winter- and summer- Environmental features dominant rainfall regimes indicates that recharge is contributing to salinity risk an annual event in winter rainfall climates (Williams et al. 1997). In contrast, recharge tends to be episodic The interaction of processes contributing salt (rainfall in summer-rainfall climates, and the effect on salinity and weathering), combined with the influence of depends on the time distribution of rainfall events other climatic and landscape features and the effects (see next section). of human activities, determine where salt is likely to In Queensland, is a useful accumulate in the landscape. average annual rainfall indicator of salinity risk. Annual rainfall ranges from The factors contributing to salting in Queensland more than 4 000 mm/yr in the coastal tropics to less differ to a degree from those occurring in other than 200 mm/yr in the south-west near Birdsville. In Australian States. These differences should be taken general, areas receiving on average more than 700 into account if information on salinity processes and mm/yr and less than 1 100 mm/yr are at the highest management options is to be applied in other areas risk of watertable salting. Areas receiving less than and climates. 600 mm/yr are not usually at risk of salinity because insufficient rain falls to satisfy plant demand and Climate and rainfall patterns recharge the ground-water. Similarly, areas receiving more than 1 500 mm/yr are also considered to be low Seasonal rainfall/evaporation patterns risk because the higher rainfall leaches salt through the soil profile. In the intermediate rainfall ranges In general, the most severe watertable salting occurs (600 to 700, 1 000 to 1 500), salinity risk is moderate. in areas where most seasonal rain falls in winter (Refer also to Average annual rainfall characteristics (Figure 13). Substantial areas of salting occur in south- page 55.) west Western Australia and Victoria, both of which experience marked winter rainfall. In Queensland, Long-term rainfall trends the greatest incidence of watertable salting occurs in coastal areas to the south, where rainfall is less Areas affected by watertable salting can fluctuate summer-dominant than in the north (Figure 13). The in size and severity in response to long-term rainfall degree of summer rainfall dominance decreases trends. from the north-east to the south-west of the State When annual rainfalls are consistently above average (Australian Water Resources Council 1976). for a number of years, this has a cumulative effect on Areas receiving winter-dominant rainfall experience groundwater recharge and the likelihood of watertable greater recharge to groundwater (and likelihood rise increases. During these periods, areas affected by of watertable rise) than areas receiving summer- recurrent waterlogging will usually be at maximum dominant rainfall (Yaalon 1983). Winter rainfall occurs size and severity. In such areas, a series of dry years during a period of low evaporative demand, so there can lower watertables, greatly reducing the rate is an excess of rainfall over evaporation. In addition, of salt accumulation that results from evaporative the rainfall is usually of relatively low intensity, concentration.
Salinity management handbook 11 Figure 13. The incidence of watertable salting in Australia correlates with seasonal rainfall patterns.
salinity hazard (mm/year rainfall) derived from 100 year median rainfall
low
moderate Ayr high 250 200 150 Nor thern Australia 100 low <600 and >1 500 50 0 moderate 600–700 JFMAMJ JASOND 1 100–1 500 Rockhampton high 700–1 100 200
150 Southern Australia 100 low <200 and >1 000 50 0 moderate 200–400 JFMAMJ JASOND 800–1 000 high 400–800 Toowoomba 200
150 key to graphs (mm) 100 rainfall 50 0 JFMAMJ JASOND evaporation
400 Merredin
300 Port Pirie Bendigo 200 300 250 250 N 200 100 200 150 150 0 JFMAMJ JASOND 100 100 50 50 0 0 0 500 1000 JFMAMJ JASOND JFMAMJ JASOND
kilometres
Figure 14. Five-year moving average rainfall patterns for In areas of Queensland where rainfall variability is Ayr, north Queensland, and Bendigo in Victoria, illustrating high, there is opportunity for salted areas to partly range and variability. The mean annual rainfall for each or totally reclaim under natural cycles. For example, location is also shown. Ayr, in north Queensland, has relatively large cyclical variations in rainfall (Figure 14). The extent of watertable salting around Ayr has varied considerably 1 500 from year to year, and even disappeared between 1 400 1982 and 1990. Surveys and air photos showed that salting only became evident when the moving average 1 300 rainfall was above 1 100 mm for a few years. (This is 1 200 discussed in detail in Moving average rainfall pattern
1 100 page 56.) Ayr 1 000 Many salinity outbreaks are first noted after periods of above average rainfall. For instance, salinity 900 outbreaks on the Darling Downs were noted in the 800
moving average rainfall (mm) early 1950s following an extended wet period. With
700 normal climatic fluctuations between drought and wet periods, salting may become apparent in susceptible 600 areas 20 to 50 years after clearing. In irrigation areas, Bendigo 500 salting can develop in much less time because of the greater input of water. 400 1860 1880 1900 1920 1940 1960 1980 2000 year
12 Salinity management handbook Landscape characteristics Human activities
Landform features In areas sensitive to hydrologic change, watertable salting can occur when human activities disturb the Watertable salting commonly occurs upslope of hydrologic balance by increasing water inputs to landscape features that restrict or inhibit groundwater the catchment or by introducing barriers to water movement or that provide preferential flow paths to movement within the catchment. the ground surface. There is a marked association between land clearing For instance: and outbreaks of watertable salting in hydrologically • Geological features, such as faults or dykes, restricted catchments, although there can be long create barriers to water flow so that groundwater time intervals between clearing and salting. This delay accumulates upslope of these barriers. depends on the degree of hydrologic change (due to • Heavy soils at the base of slopes or clays deposited clearing, irrigation, climatic variation) and the storage at the confluence of streams slow the movement and outflow capacities of the catchment. Finely of water through the soil or sediments, resulting in balanced catchments with low storage and subsurface watertable rises. outflow capacities will experience salting in perhaps a few years compared with a number of years in • When water flowing through relatively permeable catchments with greater capacities. rock types or sediments encounters less permeable underlying materials, the water flows along the line When native vegetation is cleared and an area is of the stratum rather than through it. developed for agriculture, grazing pressure and • Where rock bars or other barriers constrict the cropping practices can reduce the vegetative cover at throat of a catchment, the rate of groundwater flow times such that the vegetation cannot adequately use is reduced and water pools upslope of this point. the available water provided by rainfall. Also, most Human-constructed barriers to water flow, such as crop and pasture species are more shallow-rooted roads or dams, have a similar effect. than native species. During these periods, extra water moves below the root zone to the groundwater, (Landform features commonly associated with increasing the likelihood of watertable rise. Clearing watertable salting are described in detail in Landform in the Lockyer Valley in the early 1900s first resulted feature identification page 39.) in salinity about 30 years later, which increased markedly in the 1950s before establishing an apparent Historic salt loads equilibrium in the 1960s. Similarly, salinity developed During the period of landscape and soil formation, on cleared areas in the Bundaberg Irrigation Area salinity processes caused salt to accumulate in areas approximately 35 years after initial clearing (Kingston where drainage was poor or where watertables were 1985). close to the soil surface. As more recent climates have The use of reticulated water supplies in unsewered been drier than past climates and watertables deeper, rural residential areas can, in effect, increase the these historic salt loads are now generally at some rainfall to a landscape, disturbing the hydrology to depth in undisturbed landscapes. such an extent that extensive waterlogged or saline When the hydrologic balance of a landscape is areas develop. Landscapes under unsewered rural changed through natural processes or human residential developments can receive an equivalent activities so that a new and wetter hydrologic increase in rainfall of about 100 mm/yr (based on equilibrium is established, rising watertables can residential water supply design guidelines). Surface move salt from these historic salt loads closer to the water irrigation can contribute water inputs equivalent soil surface. to an increase in annual rainfall of some 200 to 600 mm/yr. Depending on their position and construction, Most occurrences of watertable salting in Queensland roads and dams can act as barriers to water can be attributed to the mobilisation of historic movement. Shallow watertables and seepage areas salt loads following land development. Vegetation can develop upslope of some roads and dams. patterns and soil morphological properties, such as inclusions of calcium carbonate, silcrete, ironstone, or manganese–ironstone nodules formed during extended periods of wetness in the past, are often evident in these areas.
Salinity management handbook 13 Chapter 2 — Hydrologic controls on salinity
Water is the dominant medium for salt movement in Figure 15. Evaporation, transpiration, and the role of the environment. When water is removed from the vegetation in catchment water and salt balance (adapted environment by processes that exclude salt, such as from Dowling & Gardner 1988). Used with permission from evaporation and transpiration, salt is deposited and CSIRO. accumulates over time (Figure 15). Evaporation occurs at the soil/atmosphere interface water out Q in where groundwater seeps at the soil surface or where (pumps trees crops) the watertable is close enough to the soil surface for capillary action to draw water to the surface. Another salt in source of salt accumulation is evaporation of surface water. This is important in areas where salt is not salt out regularly flushed out of the catchment, such as in alluvial headwaters distance Lake Eyre.
Q = quantity of water Transpiration occurs at the soil/root interface Q out alluvium at the confluence with the next surface stream where plants absorb water from the soil, generally excluding salts dissolved in the water so that these When trees are removed, water usage in the system salts accumulate in the root zone. When vegetation generally decreases, runoff slightly increases, and has root systems reaching to a deep watertable, salt the resulting excess water may percolate through accumulates at greater depths in the soil profile or soils and weathered rock into the watertable. If lateral over a larger depth range above the watertable. drainage is poor, the level of the watertable will rise, Hydrologic equilibrium results from a balance establishing a new hydrologic balance in the system. between climate (largely rainfall and temperature) The salinity of the groundwater may increase as and the development of a landscape (including additional salt is dissolved from weathered rocks and weathering/soil formation and vegetation pattern). soils not previously below the watertable. The presence of a discharge area indicates that the Thus vegetation provides a buffer in the system, rate of water movement into the groundwater of the with the capacity to utilise the available water in the catchment exceeds the rate of water movement out landscape. There are limits: if rainfall is so low that of the catchment. Thus, only hydrologically sensitive plants cannot grow or reproduce (for example, the catchments (without effective vegetative or soil water Sahara Desert and to a lesser extent the Simpson storage buffers) will exhibit waterlogged or saline Desert), vegetation will be limited or absent; if rainfall discharge areas. is so great that it exceeds the ability of any vegetation Soil hydraulic properties govern the height to which to utilise the water (that is, the rainfall exceeds the the capillary fringe of the watertable can rise within a potential evapotranspiration capacity of plants which given soil. When the capillary fringe intersects the soil is determined by the radiation energy), there will be surface, soil hydraulic properties also determine the an excess of water. In the second case, the landscape maximum rate at which groundwater and dissolved adjusts to the extra water through geomorphological salts can be transported to the soil surface. If the daily processes such as enhanced weathering, erosion, evaporation rate exceeds the supply of groundwater gully formation, and increased baseflow in streams. to the soil surface, the soil dries and capillary rise is greatly reduced. In undisturbed areas, the native vegetation is Groundwater movement model generally in equilibrium with the natural hydrology The spatial distance between areas where recharge of an area. Trees normally utilise all the available and discharge occurs will vary from catchment to water and remove water from the area by catchment. In some cases, these areas may overlap; evapotranspiration. A small proportion of rainfall in others, the recharge and discharge areas may be (less than 10%) evaporates from the surfaces of separated by thousands of kilometres, as in the case grasses and the leaves of trees. In this situation, the of the Great Artesian Basin (Figure 16). In Queensland, vegetation is able to cope with and moderate the the distance between recharge and discharge areas effects of variations in seasonal and yearly rainfall. is usually in the range of a few hundred metres to several kilometres.
14 Salinity management handbook Figure 16. Recharge areas, natural discharge areas (springs), and directions of regional groundwater flow in the Great Artesian Basin (Habermehl 1980). Commonwealth of Australia copyright reproduced by permission.
o o 136o 142 148
Mt Isa
0 200 km 22o NT QLD
Rockhampton
Brisbane
Lake Eyre 30o SA
Lake Frome recharge Broken Hill NSW discharge Lake Torrens Lake Gairdner direction of flow Newcastle
A simple conceptual model is useful for understanding Recharge how water moves salt through the landscape. In this model, which focuses on the movement of Recharge is the process of water entering the groundwater, the landscape is divided into areas groundwater. Recharge areas are areas where the net where water predominantly enters groundwater movement of water is into the groundwater. Relatively (recharge), moves laterally (transmission), and exits permeable areas of the landscape, usually on the from groundwater (discharge). The model is illustrated upper slopes and on shallow soils, act as recharge in Figure 17. areas.
Salinity management handbook 15 Figure 17. A simple conceptual model which considers a Soils are deeper and less permeable than those in landscape in terms of recharge, transmission and discharge recharge areas. areas. The depth to the watertable in transmission zones is recharge area usually less than in recharge areas, with less marked seasonal fluctuations (Figure 18).
Figure 18. Typical seasonal fluctuations in hydraulic head in transmission zone discharge area recharge areas, transmission zones and discharge areas for wa tertable one site on the Darling Downs (after Thorburn et al. 1986).
405 recharge area AHD) metres ( 404 The critical parameters in determining the rate of recharge are soil properties and depth, rainfall and 397 evaporation patterns, and vegetation type. Soil properties influencing recharge include: head transmission zone 396 • characteristics of the macropores, which transport 388 water to the groundwater when the soil is saturated • the drainable porosity of the soil, which is the
hydraulic discharge area capacity of the soil to release water between 387 saturation and the point where water ceases to drain readily (field capacity) 200 • plant available water capacity, which is the capacity 150
of the soil to retain water between an upper limit 100
determined by the field capacity and a lower limit 50
when water becomes unavailable to plants (wilting monthly rainfall (mm)
point). JASONDJFMAM JJASOND JFMAMJ JASOND JF 1982 1983 1984 The effectiveness of vegetation in exploiting available soil water, particularly at depth, varies depending on factors such as growing season, rooting depth, Discharge drought tolerance, and vegetation density. Discharge areas are areas where the net movement Recharge is maximised where: of water is upwards/outwards from the ground. • soils are shallow overlying fractured rocks They generally occur where there is some hydrologic • soils are highly permeable, or outcrops of fractured restriction to downslope water transmission, causing rock occur water to flow toward the soil surface where it • vegetation is shallow-rooted or absent ‘discharges’ from the groundwater. Discharge areas often occur where the ground is flat or poorly incised. • the rainfall pattern is characterised by rainfall in In a range of landscape types that are particularly excess of evapotranspiration for a period of the susceptible to watertable salting, discharge areas year. occur in characteristic positions in the landscape The depth to the watertable in a recharge area is (described in Landform feature identification page usually considerable. Watertable level tends to 39). Soils in discharge areas are generally deeper respond quickly to rainfall with marked seasonal and less permeable (because of higher clay content) fluctuations (Figure 18). than in recharge and transmission areas. This is because past weathering products of upslope areas Transmission accumulate in discharge areas. Transmission areas occur where the dominant The watertable in a discharge area is usually at or near movement of water within the groundwater is the soil surface, with subdued seasonal fluctuations approximately parallel to rather than toward or away compared with recharge and transmission areas from the soil surface. Transmission areas generally (Figure 18). Waterlogging and salinity usually manifest occur in areas of intermediate and decreasing slope. in discharge areas. Salt accumulates when water is removed by evaporation and transpiration and
16 Salinity management handbook salt is left behind. However, land use changes and through the barrier into the deeper regional ground- landscape features in recharge, transmission and water and/or move laterally to toeslopes and/or discharge areas will determine the extent and severity be used by vegetation through evapotranspiration. of salting in discharge areas. Water in a perched water body builds up following significant rainfall events, and may be present During rainfall periods, surface salt accumulations for weeks or a few months. Irrigation can produce in discharge areas are leached downwards into perched watertables in a similar manner. the root zone, particularly if the watertable is low following a number of drier than average years. Discharge is maximised where: During a subsequent wetter than average cycle, salt • the watertable is at or very close to the soil surface accumulated in the root zone will be moved upwards (salt accumulation is generally greatest when the by the rising watertable. Thus, through a series of wet watertable is permanently between 0.5 and 1.5 and dry cycles, salts continue to accumulate in the metres below the soil surface) soils and groundwater in discharge areas. • the soil surface is bare or sparsely vegetated The form of salting in a discharge area depends on • soil properties at the site allow a maximum rate of the rate of upward water movement to the soil surface water movement through the surface layers. compared with the rate of evaporation at the soil surface. Three situations can result: • If water moves upward through the soil more Salt mass balance quickly than it evaporates at the soil surface (rate of Salt mass balance refers to an equilibrium between water rise exceeds evaporation rate), a seepage will salt entering and salt leaving the catchment. For develop. The salinity of the seepage will depend on instance, salt entering the catchment in the form of the salinity of the groundwater. a large volume of water with low salt concentration, • If the capillary fringe of a shallow watertable moves such as rainfall, can be in balance with salt leaving water to the soil surface at approximately the same the catchment as a trickle of outflow of very high salt rate as evaporation removes water from the soil concentration (refer Figure 19). The accession of salts surface, salt will accumulate on the soil surface at from weathering and rainfall and the export of salts the maximum rate. Salt will be more concentrated through stream flow and groundwater discharge are in this situation than in the case of a permanent in equilibrium. In periods of adjustment between or seasonal seepage, which would allow any changing inputs or outputs, there will be a change accumulated salt to be periodically flushed away. in the salt storage in the landscape until the new • If water evaporates from the soil surface more equilibrium is attained. The salt storage may increase quickly than it moves upward through the soil and or decrease or, most commonly, salt mobilisation if the watertable is deep enough that capillary rise will cause a translocation of salt within the existing to the soil surface is not significant, vegetation may storage. maintain the area in hydraulic balance without any This is described by the steady state mass balance salt concentration at the soil surface. However, equation: salt will accumulate in the root zone as plant roots Qici = Qoco ...... 1 continue to take up water and exclude salt. The magnitude of this accumulation will depend on the where
salinity of the groundwater and the extent to which Qi is quantity of water entering the system rainfall flushes salt away from the soil surface or ci is salt concentration of the water leaches salt through the soil. entering the system
On the basis of current experience in Queensland, Qo is quantity of water leaving the system areas where the watertable is less than 6 metres co is salt concentration of the water leaving deep under undisturbed vegetation have the greatest the system. potential to develop watertable salting when subject to clearing or other land development. Deeply incised Parameters creeks can prevent watertable rise, but these do not usually occur in areas susceptible to salting. This steady state equation can be expanded to incorporate other processes that control the Groundwater encountered in topographic positions movement and quantities of salt in the system, above valley floors is usually associated with such as dissolution and weathering. In the following perched watertables. These form when downward figure (Figure 20), mass balance inputs and outputs percolating water (from rainfall and runoff) is held up are indicated on a diagrammatic section through a by impermeable layers in the weathered zone. The catchment: water in the perched water body may slowly percolate
Salinity management handbook 17 Figure 19. Schematic diagram of salt balance in a landscape system based on the Lockyer Valley where the Winwill conglomerate forms a geological restriction to groundwater flows (Gardner 1985a).
Q = quantity of water
deep drainage deep drainage
creek bed leakage
historic soil salt
Q in capillar y rise
historic soil salt Q out
groundwater erate restriction
Winwill conglom
recharge area transmission zone discharge area Qs is quantity of surface seepage flowing away from the discharge area Q c r r (including base flow in drainage lines intercepting the discharge area) Q Q Q c e t d d cr is salt concentration of rainfall Qru ce ce cd is salt concentration of the water
ct draining below the root zone
Qg cg cw is salt concentration of the water Q (c + c ) Q (c + c + c ) d d w d d w s attributable to rock weathering and dissolution Figure 20. Diagrammatic section through a catchment indicating mass balance inputs and outputs (Shaw 1993). ch is salt concentration due to the dissolution of historic salt storage in where the discharge area Qr is quantity of rainfall ce is salt concentration due to salt on the Qd is quantity of water draining below the soil surface resulting from evaporation root zone ct is salt concentration in the root zone of Qe is quantity of water evaporated from the vegetated areas due to transpiration soil surface in the discharge area cs is salt concentration of water seeping Qt is quantity of water transpired by from the groundwater in the discharge vegetation in the discharge area area (including base flow in drainage
Qg is quantity of groundwater flowing away lines intercepting the discharge area) from the discharge area (subsurface cg is salt concentration of the groundwater outflow) flowing away from the discharge
Qru is quantity of surface runoff across the area (this is equivalent to the sum discharge area cd+cw+ch+cs).
18 Salinity management handbook Table 2 Expected range of values for parameters in Figure 20 for salt-affected catchments in southern Queensland. Each value is also expressed as a ratio of Qd (quantity of water draining below the root zone in dominantly recharge areas) and cd (the concentration of this drainage water) as appropriate.
Quantity Concentration
Symbol Range Typical value As a ratio of Symbol Range (dS/m) Typical value As a ratio of cd (mm/yr) (mm/yr) Qd (dS/m)
Qr 300–2 000 800 27 cr 0.02–0.2 0.003 0.1
Qd 2–150 30 1 cd 0.1–0.5 0.3 1
cw 0.1–1.0 0.6 2
ch 1–100 15 50
Qe 100–2 000 800 27 ce 1–500 30 100
Qt 100–1 500 500 17 ct 1–20 12 40
Qg variable small - cg ∑(cd+cw+ch+cs) 10 33
Qru 50–200 100 3
Qs very low small very small cs cg–cc 10–30 33–100
Typical values Parameters
Ranges of values that can be expected in salt mass Hydraulic conductivity balances in southern Queensland have been compiled using information from salt-affected catchments in Hydraulic conductivity refers to the property of a soil these areas (Shaw 1993). The catchments from which or other porous material to conduct water. Hydraulic this information was gathered received summer- conductivity is characteristic for different materials, dominant rainfall of between 600 and 1000 mm/yr and depends on the pore size distribution of the with class A pan evaporation of around 2000 mm/yr. material’s matrix. These values are shown in Table 2. The hydraulic conductivity of soils is quite variable From the data in Table 2, three processes stand out and is greatest when soils are saturated. Rainfall as contributing to salting: the mobilisation of historic entering a recharge area wets the soil. salt, evaporation and transpiration. The mobilisation The water content of the soil increases until the soil of historic salt can contribute 50 to 100 times more is saturated. At this stage, water can move directly salt than rainfall. Evaporation from the soil surface through the macropores and may bypass part or all of and evapotranspiration by vegetation are significant the soil matrix. Macropore characteristics differ with processes concentrating salt as well as removing soil types; for instance, macropores in swelling soils water from the catchment. operate for only a short time until swelling reduces their size. Water drains readily from the soil until the water content approximates field capacity. At water Rate of water movement in the contents less than field capacity, water movement landscape usually becomes very slow (and is treated as negligible in the following calculations). The long-term The rate at which water moves through porous (saturated) hydraulic conductivity of soils in significant materials (soils or aquifers) in the landscape depends recharge areas is in the order of 10 to 100 mm/d (0.01 on the hydraulic conductivity of the material through to 0.1 m/d). which the water is flowing, the hydraulic gradient driving the flow, the area available for flow, and the The hydraulic conductivity of an aquifer transporting period of flow. This is described by Darcy’s Law (which water would be in the order of 0.5 to 10 m/d. In expresses flow per unit area per unit time): comparison, at a point in the catchment where salting occurs because groundwater flow is restricted, the Q/A = K∆H ...... 2 hydraulic conductivity may be 10 times less (0.05 to where 1 m/d). Q/A is volume of water flowing through a unit cross-sectional area per unit time (example units are m3/m2/day) K is hydraulic conductivity of the porous medium (for example, m/day) ∆H is hydraulic gradient in the aquifer (for example, m/m). Salinity management handbook 19 Hydraulic gradient Time period The hydraulic gradient, the driving force acting on In summer rainfall areas, soils are typically saturated the groundwater, is the difference in hydraulic head for only a few days each year. For saturated hydraulic between two horizontal points (usually points of conductivity to operate, there must be free water recharge and discharge) over the horizontal length at the soil surface to be conducted through the over which this difference occurs. In an unconfined larger pores. This may occur for only two to five days aquifer, the hydraulic gradient is effectively the each year. In comparison, a groundwater aquifer is gradient of the watertable. saturated all year round and can conduct water every day of the year. In a permeable soil, the vertical gradient driving recharge is mainly gravity; for every metre of saturated Table 3. Illustrative hydraulic parameters for a generalised soil depth, there is a hydraulic head of 1 m resulting salted catchment of 1000 ha, with bare or seepage areas in a hydraulic gradient of 1 m/m. For water moving establishing a hydrologic equilibrium between recharge horizontally, the driving gradient is the slope of the and discharge. watertable, so groundwater flow is much slower. The Parameter (and units) Symbol Recharge Subsurface hydraulic gradient of water moving in the groundwater outflow is commonly in the range of 1:100 to 1:1 000 m/m. Hydraulic conductivity K 0.006 10 The transmission of actual water (or salt) molecules (m/d) from the point of recharge to the point of discharge Hydraulic gradient ∆H 1/1 1/100 takes quite some time. For example, in the Burdekin (m/m) Irrigation Area (left bank) in north Queensland, the Area (m2) A hydraulic gradient is approximately 1:2 300 m/m (11 recharge = surface 10 x 106 m difference in hydraulic head between recharge area and discharge areas; 25 km from recharge area to discharge = cross- 5 x 102 discharge area, in this case, the sea). Employing sectional area Darcy’s Law, a molecule of salt in this catchment Time period (d) t 2 365 would take in the order of 300 years to travel from Volume of water 120 ML/ 18.2 ML/yr the recharge area to the sea. (A rule of thumb for water yr movement through an aquifer is one to two metres per week.) Interaction of parameters However, salting obviously occurs over much shorter time periods than this. This is because water added In an unsalted catchment at hydrologic equilibrium, to the groundwater system as recharge transmits recharge will be balanced by subsurface outflow. pressure in the groundwater to the discharge point; However, in a salted catchment the rate of recharge it is the equalisation of this pressure that causes the will exceed the rate of subsurface outflow. The volume watertable to rise in discharge areas. of outflow may be restricted by the cross-sectional area of the aquifer at the point of discharge or by Based on these examples of the influence of gradient reduced hydraulic conductivity. on water flow, most salting outbreaks will result from the mobilisation of historic salt moving vertically Discharge areas develop only after the unsaturated within the soil profile rather than the inflow of salt soil water storage is filled and the watertable rises. from naturally saline aquifers. The period during which the soil water storage becomes saturated provides the lead time that Area occurs between the initial hydrologic change and the subsequent development of discharge areas. This The surface area of a catchment through which water lead time can range from a few years to up to 50 years. enters the groundwater as recharge is often much larger than the area through which groundwater can Table 3 shows generalised figures for a salted flow out of the catchment. For example, a 1 000 ha catchment of 1 000 ha (that is, 10 x 106 m2) with, say, catchment with developed salting may have restricted 10% of the catchment having a high recharge rate of subsurface outflow through an aquifer perhaps 100 20 mm/d (0.02 m/d), 20% of the catchment having m wide by 5 m deep. Thus, potential recharge is a lower recharge rate of 10 mm/d (0.01 m/d), and occurring over a surface area of 10 x 106 m2 (although the remaining 70% having a low recharge rate of 3 not all recharge will be at high rates), whereas outflow mm/d (0.003 m/d), averaging over the recharge area is occurring through a cross-sectional area of 500 m2. to 0.006‑m/d. In this illustration, subsurface outflow is likely to occur every day of the year, but recharge will only occur when the soil is saturated down to the watertable—perhaps only two days each year.
20 Salinity management handbook The difference between recharge and subsurface outflow (here, between 120 and 18.2 ML/yr) is the volume of water that the system must remove in other ways. In this situation, the system will compensate and discharge will be increased via: • increased surface seepage • increased evaporation from a discharge area with a watertable near the soil surface (At an evaporation rate of 2 mm/d, 73 ML/yr of water will be removed from 10 ha of bare discharge area.) • increased evapotranspiration from vegetated areas in a low salinity discharge area (due to increased vigour of growth in response to increased water availability).
Salinity management handbook 21 Chapter 3 — Salinity and hydrology management
Managing salinity by managing groundwater balance A discharge area can be managed by increasing the outflow of groundwater from the catchment until outflow exceeds recharge. However, increasing outflow simply by increasing evaporation and transpiration in the discharge area may not be sustainable in the long term. This is because salt remains and is redistributed to the soil surface or within the root zone. Vegetation in the area will die unless it is able to cope with the more saline conditions. Both the water and salt balances need Figure 21. A de-watering bore located within a groundwater to be considered because water is the transport discharge area near Yass, New South Wales. mechanism for salt. Evaporation from surface soil is an energy- efficient means of removing free water since the Managing soil salinity by actual evaporation rate often exceeds the actual managing leaching fraction transpiration rate of vegetation (particularly if the Accumulated salts can be periodically flushed from vegetation is affected by waterlogging or salt) and the soil profile by seasonal rains or by regular or may approximate potential evaporation rates. specific applications of irrigation water. Leaching Talsma (1963) determined the critical depth of fraction is the term given to the portion of applied watertables at which groundwater supply equalled the water that is required to drain through the root zone daily evaporation rate for several soils. The results for to maintain soil salinity at acceptable concentrations. a medium clay and a loam are shown in Table 4. USSL (1954) used the term leaching requirement and expressed it in terms of the steady state mass balance Table 4. Watertable depths at which upward water model discussed earlier: movement from the watertable equals daily class A pan c Q evaporation rate for two soils (after Talsma 1963). LR = i = o ...... 3 c o Qi Depth to watertable (m) for daily where evaporation rate (mm/d) Soil type LR is leaching requirement 1 2 4 5 8 10 Qi is quantity of water entering the soil Medium clay 1.3 0.9 0.6 0.5 0.4 0.4 (usually expressed as depth)
Loam 2.0 1.6 1.3 1.2 1.1 1.0 Qo is quantity of water draining below the root zone
ci is concentration of water entering the Watertables have to be shallower in heavier clay soils soil (usually expressed as electrical and under conditions of higher daily evaporation rates conductivity) (for example, in summer) before maximum capillary co is concentration of water draining below rise and salting will occur. Surface mulching can the root zone (salinity of deep drainage reduce the evaporation rate considerably. Dd). Experience in Queensland, where daily evaporation This calculation has proved popular for long-term rates generally exceed 5 mm/d, suggests that equilibrium situations, although it is strictly only watertables need to be within one metre of the soil correct where no precipitation of salts or ion exchange surface for a considerable part of the year for serious occurs within the root zone. surface soil salting to develop. Under dryland conditions, Qi can be readily measured as rainfall and Ci as rainfall salt concentration. Assuming Co of the drainage water is in equilibrium with the salt concentration of the soil matrix at a
water content approaching field capacity, oQ can be estimated. 22 Salinity management handbook Since it is difficult to determine the amount of water Figure 22. Changes in soil salinity of two soils with years draining below the root zone, an estimate of drainage under irrigation in the Emerald Irrigation Area (data is usually obtained by relating salt concentration at courtesy of Don Yule). depth to the concentration of the input water (rainfall and irrigation water) weighted for volume of input. In 0 symbolic terms: numbers 0–9 indicate number of years of irrigation Qo cr + Qiw ciw Rainfall weighted ci = ...... 4 Qi + Qiw where 0.5 Qr is quantity of input water due to rainfall Q is quantity of input water due to irrigation iw )
cr is concentration of input water due to
rainfall depth (m 1
ciw is concentration of input water due to irrigation. This approach assumes that the soil salt content at the bottom of the root zone reflects the concentration 1.5 60 9564301 of water draining below the root zone. Deep drainage basaltic clay alluvial clay and salt balance in a particular soil are influenced by vegetation, rainfall, evaporation, landscape position 0 0.5 1 1.5 EC (dS/m) and soil properties such as infiltration rate, available 1:5 water storage capacity and texture. Table 5 highlights the range of leaching fraction values The impact of irrigating with saline and moderately encountered for various soils under rainfall. sodic waters on a clay soil in the Lockyer Valley is shown in Figure 23. However, both the salinity and the sodicity of applied water affect soil stability, dispersibility and Many irrigation water quality guidelines promote permeability (discussed in the following section). managing soil leaching by varying the amount of water applied. This works well with permeable soils. Table 5. Rough guide to how leaching fraction varies with However, in slowly permeable soils (for example, soil properties (from Yo & Shaw 1990). 1 to 10 mm/d), soil properties and sodicity are the dominant controls on leaching rates and reduce the Soil texture Assumed LF Range effectiveness of irrigation water management. In sand 0.4 0.3–0.6 clay soils, leaching is strongly influenced by the salt loam 1.15 0.1–0.3 concentration and sodicity of the irrigation water. light clay 0.15 0.05–0.2 (Calculating leaching fraction using simple empirical heavy clay 0.1 0.05–0.2 relationships is covered in Leaching fraction page 32.) clay soils with heavy clay 0.05 0.002–0.1 This problem is obvious with any high-sodium water subsoils or very poor structure during and following rainfall because the salt in with poor subsoil wetting the surface layers is washed out by rainfall, leading When soils are irrigated with good quality (low to dispersion and crusting. Very low salinity water salinity/sodicity) water, the amount of rainfall is almost always results in water infiltration problems, effectively increased. This increases leaching, and regardless of the proportion of sodium ions in the over a period of time a new salt content equilibrium water (Ayers & Westcot 1985). Assessing irrigation will be established in the soil. Irrigation with good water quality with soil properties and behaviour is the quality water can result in significant removal of salts best way to avoid these problems. from the soil profile, as was seen in the Emerald Irrigation Area (Figure 22). A new equilibrium is Soil stability and sodicity established when the final soil salt concentration is balanced by the amount of water available and the The mineralogical structure and behaviour of clay sodicity of the soil. minerals have been described in a range of textbooks such as van Olphen (1977) and Bolt (1979). Ion substitution in the clay mineral lattice creates a negative charge on the clay mineral, which attracts cations to the mineral surfaces.
Salinity management handbook 23 Figure 23. Changes in salt content A) and exchangeable sodium percentage B) profiles under irrigation for the Tenthill soils in the Lockyer Valley (Shaw et al. 1987).
A) salt content B) exchangeable sodium percentage
chloride concentration (mmolec/L in soil water at Wmax ) exchangeable sodium percentage 0 30 60 120 180 0 246810 12 14 0 0 0.1 0.1
0.3 0.3
0.6 2E depth (m) 0.6 2D
3B 2C 0.9 3A 2D
2A depth (m)
0.9
1.2 3B Irrigation water (key to Figure 23) Soil Assumed Chloride EC ds/m SAR 1.2 texture LF mmolec/L 2C 2A 3A 3A nil nil nil nil 2E 2E nil nil nil nil 1.5 3B 30 26 1.6 1.2 2D 9 13 2.0 1.3 The balance between the attractive and repulsive 2C 5/22 9.8 3.5 2.0 forces between clay particles determines the degree 2A 45 55 7.4 6.8 to which a soil will swell or disperse when it is wetted. Swelling is promoted by repulsive forces associated *changed water quality sites 3A & 2E are non-irrigated sites with hydration. If the layer of cations is thick and diffuse (for instance, a cation layer dominated by These cations, called exchangeable cations, balance sodium cations), the greater repulsion between clay the negative charge of the clay mineral. The properties particles will result in increased particle separation of the layer of adsorbed cations are determined by and dispersion. the nature of the clay mineral (particularly surface Montmorillonite-dominated clays are more stable charge density and surface area) and the composition than clays dominated by other clay minerals. This is and concentration of the surrounding solution. For because montmorillonite clay minerals attract divalent example, a high proportion of sodium in the soil ions such as calcium (Ca2+) and magnesium (Mg2+) in solution will result in a high relative proportion of preference to monovalent ions such as sodium (Na+) sodium among the exchangeable cations. These and potassium (K+). In contrast, illite minerals display characteristics of cations, mineral and surrounding no ionic preference. solution determine clay behaviour. Several researchers have identified a non-uniform The attractive forces between clay particles are mixing of divalent and monovalent cations on strongest when the exchangeable cations are mostly montmorillonite. For example, Shainberg et al. (1980) calcium and weakest when the exchangeable cations considered the affinity of the internal surfaces of are mostly sodium. This is because the cation layer montmorillonite for Ca2+ to be between two and 15 for the divalent calcium cations is smaller, making the times greater than the affinity of the external surfaces. distance between the clay particles smaller. This is Thus in low to moderate Na+ concentration solutions, the main factor contributing to the stability of calcium- only the outside layers of montmorillonite clay dominated clays (Quirk & Murray 1991). minerals will be affected by sodium, contributing to the greater stability of montmorillonite or cracking clay soils.
24 Salinity management handbook Aggregates may slake and/or disperse on wetting. The threshold values can be idealised into three Slaking is the macroscopic breakdown of an regions as shown in Figure 24. Line 1 is almost parallel unsaturated aggregate on immersion; dispersion to the Y axis and shows a very limited effect of an is the process of part of an aggregate going into increasing proportion of sodium ions adsorbed onto suspension (Emerson 1968). the clay mineral surfaces (ESP) on salinity (EC). Such soils respond to the mechanical effects of bonding The behaviour of clay minerals with sodium has and cementing of clays in soils with low clay contents, been described by a mechanical model and a rather than to physico-chemical effects. Typical of this physico-chemical model (Olsen & Mesri 1970). In response would be the behaviour of kaolinitic soils the mechanical model, clay behaviour is not very associated with large amounts of iron oxides and the responsive to salt concentration; this is because the behaviour of acid clay soils with aluminium as the clay is based on the interaction of particle shape, dominant exchangeable cation. particle friction and the geometric arrangement of particles. In the physico-chemical model, salt Figure 24. A conceptual framework of soil response to ESP concentration and ESP cause major changes in clay and ECse (Shaw 1996). (The lines are described in the text.) behaviour. 50 The mechanical model describes the behaviour 1 of kaolinite clays fairly closely because kaolinite crystals are large and not particularly responsive to 40 salt concentration. On the other hand, the physico- 2 kaolinite chemical model better describes the behaviour of montmorillonite clay minerals because these minerals 30 are responsive to the physico-chemical nature of
the medium. Illite clay minerals are intermediate in ESP montmorillonite behaviour. 20 Mixtures of clay minerals are most sensitive to mixed mineralogy exchangeable sodium. Arora and Coleman (1979) found that the order of clay mineral susceptibility 10 to dispersion in sodium bicarbonate solutions was illite (most) > vermiculite > montmorillonite > kaolinite 3 (least). 0 Rengasamy and Olsson (1991) represented (in 02 46810 ECse(dS/m) diagrammatic form) the stages and force strengths of slaking, dispersion and flocculation of aggregates under wetting and drying. The mechanisms suggested In region 2 (the intermediate region in Figure 24), the by Rengasamy and Olsson involve wetting air dry soils respond to an increase in ESP with an increase aggregates such that the repulsive forces generated in EC. This is the region of true physico-chemical by wetting result in slaking. In a calcium-dominated response and is typical of many soils. Kaolinite is least clay, attractive forces dominate within the micro- sensitive to the physico-chemical response, whereas aggregates, resulting in greater stability. As the illite and mixed mineralogy soils are most sensitive particles continue to wet, sodium-dominated systems to sodium. Montmorillonite-dominated soils that can will demonstrate spontaneous dispersion due to the restructure on wetting and drying are intermediate in repulsive forces in the exchangeable cation layer. A sensitivity to ESP as assessed by EC (Shaw 1996). point is reached where the repulsive and attractive Line 3 represents the other boundary of the physico- forces are balanced. If the salt concentration of the chemical soil response. The pattern of line 3 would surrounding solution is raised, flocculation will occur. only occur in soils with no cation exchange capacity The point at which soil just flocculates can be termed and thus no ability to increase ESP, and with no the threshold value; this is the balance between effective leaching below the root zone. In such soils, repulsive and attractive forces such that the soil soil dispersibility is not likely to increase and EC is remains stable and not dispersed. likely to increase. This would not occur in normal If external energy is applied (mechanical dispersion), field soils. the clays will disperse when the strength of the repulsive forces exceeds the strength of the attractive forces. Because these processes affect soil structure, they also affect hydraulic conductivity.
Salinity management handbook 25 When irrigation waters with a high proportion of sodium ions compared with other cations are added to soil (high SAR, described in Sodicity in soils and waters page 37), sodium displaces other cations on the clay mineral exchange sites. This increase in the sodicity of the soil generally results in soil dispersion with consequent soil surface sealing, crusting, erosion, poor water entry and poor seedbeds. Ham et al. (1993) reported problems with low salinity, low sodicity irrigation waters in the Burdekin Irrigation Area on silty soils prone to surface dispersion. The effects were attributed to insufficient salts to maintain soil flocculation in the soil surface. This is commonly reported worldwide with low salt content irrigation waters.
26 Salinity management handbook Part B — Investigating
4 Features of salinity investigations
5 Measurement techniques and relationships
6 Landscape characteristics and salinity mapping
7 Vegetation
8 Climate and rainfall patterns
9 Soils
10 Waters
11 Water quality
12 Human activities
Salinity management handbook 27 Chapter 4 — Features of salinity investigations
Salinity is the result of the complex interaction of Features of salinity investigations are listed and the geologic history, past climate, climate, vegetation, information they contribute to salinity investigations geomorphology (geology and landforms in are discussed here in Table 6. In Answers to common combination), and land and water development questions about salinity (page xi) in the front of this activities on sensitive landscapes. Because of the handbook, features of salinity investigations that diverse nature of these interacting factors, there is no need to be undertaken to provide an initial assess- one aspect or factor that can identify the risk ment of salinity, and features that make up more of salinity or the likely extent of possible salinity detailed investigations are discussed. problems. Effective management strategies need to be based on salinity risk assessment as well as processes affecting salinity development.
Table 6. Features of salinity investigations.
Feature Information contributing to salinity investigations Level Page I : Initial D : Detailed M : Monitoring Landscape characteristics and salinity mapping Landform feature • Identifies landform features that are hydrologically sensitive and I : Initial, D 39 identification susceptible to salinity • Indicates specific landscape positions where salinity is likely to occur • Indicates areas and landforms most at risk of salinity under changed land use and hydrological conditions • Can provide information about discharge and recharge areas Geology • Can indicate likely sources of salts I, D 42 • Can reveal geological structures and rock types controlling water movement in the landscape, and provide information on aquifer characteristics Landscape salinity • Provides information about the current extent and severity of I (if equipment 43 mapping salting available), D, M • Can be used to locate historic salt loads
Vegetation Plant communities as • Indicates location and extent of any current or recurrent salt- I 49 salinity indicators affected areas • Can be used to locate areas for more detailed investigations • Useful in uncleared or partly cleared areas or areas under pasture Vegetation patterns • Variations in density, species composition and vigour can indicate I (field 50 on remote sensing • Changing vegetation patterns on air photos over time can provide a observations), images historical perspective of cyclic variations in salinity and the effects D (remote sensing) of land use and development Planr response to • The appearance of individual plants—stunted growth, leaf effects— I, D 51 salinity and specific can indicate plant responses to salinity or high levels of specific ions ions Climate and rainfall patterns Average annual • Indicates whether land in the region is at risk of watertable salting I 55 rainfall characteristics as characteristics indicated by the correlation between watertable salting occurrences and rainfall patterns
28 Salinity management handbook Feature Information contributing to salinity investigations Level Page I : Initial D : Detailed M : Monitoring Moving average • Indicates where the current time fits into long-term rainfall D 56 rainfall pattern patterns, pattern and potential for increased or decreased salinity with changes in water inputs (from rainfall or irrigation) over the medium- to long-term Soils Soil properties • Indicates areas with a history of waterlogging or salting I 58 Soil salinity • Provides guidelines for the potential of the soil for cropping, I, D, M 60 pastures, trees Soil salt profiles • Indicates current salinity levels and dominant hydrological process I (field 1:5), D 61 • Provides information for choosing species to plant, based on plant (laboratory soils salt tolerance data analysis), M • Can be used to approximately locate recharge and discharge areas and to estimate recharge Soil sodicity • Provides information on soil stability and potential for soil D, M 63 response under irrigation • Provides information for erosion control measures that may be required Water Field tests for waters • Indicates salt concentrations, and initial suitability of water for I (existing water) 65 various uses (sampling points), • Mapping water salinity in surface waters and existing groundwater D, M sampling points can indicate salt sources and salinity distribution Use of piezometers • A network of bores or piezometers can be used for regional I, D, M 66 mapping of groundwater and restrictions to groundwater flow • Monitoring provides insight into processes • Water level contours can indicate barriers to water flow • Suitable for monitoring the effects of management and rainfall variability Catchment • Provides an initial assessment of the magnitude of the water I, D, M 70 groundwater balance imbalance balance estimation • Provides information on the amount of water to be managed to reclaim saline areas Water chemistry • Analysis can be used to indicate likely geologic sources of salts 73 and salt sources which can sources identification be linked with the actual position identification of these salt sources in the landscape to interpret hydrologic processes • Indicates mixing of waters and salt concentration processes Water quality Human domestic use • Analyses will indicate suitability for human domestic use I, D, M 79 Stock watering • Analyses will indicate suitability for stock watering I, D, M 79 Irrigation • Analyses will indicate suitability for irrigation depending on soils, I, D, M 81 climate and crop type • Analyses will indicate potential effects on soil and likelihood of contributing to soil degradation Human activities Human land use and • Can be useful for identifying specific areas where salinity may I (oral history), 88 records have occurred records in the past, and in conjunction with five- D (air photos, year moving average rainfall information can indicate areas of management y the landscape most at risk of salinit under changed hydrologic records etc.) conditions • Provides a historical perspective on how human activities have contributed to the development of salting • Farm records on land development, bores, water levels etc. can be used to identify past hydrological changes
Salinity management handbook 29 Chapter 5 — Measurement techniques and relationships Electrical conductivity as a A common method for determining saturation water content is mixing the soil with water until the soil measure of salinity paste glistens and begins to flow, and then extracting Salinity in soils can be estimated conveniently from the solution by filtration under vacuum or pressure, the electrical conductivity (EC) of a soil solution. Many or by centrifuging. An alternative method is to wet salts dissociate to ionic form in water (which, when the soil sample on a tension table where the soil is pure, has a very low conductance), so the electrical placed on a porous material hydraulically linked to conductivity of a solution provides a measure of total free water usually 1 cm below the sample. However, concentration of salts. there are problems with these techniques because the wetting end point is not easily reproducible, and Three measures of electrical conductivity are: with the tension wetting method, the quantity of water
• EC1:5—the electrical conductivity of a 1:5 soil water taken up by the soil depends on the rate of wetting, suspension, used routinely in analyses the nature of the clay and the amount of exchangeable sodium. (Details of methods are given in Rayment and • ECse—the electrical conductivity of the soil saturation extract, used for predicting plant Higginson 1992.) response (commonly predicted from 1:5 and soil Water (and hence salt) movement in soils becomes properties, or can be measured directly) very small once the soil water content is drier than
• ECs—the electrical conductivity of soil at measured maximum field water content (roughly equivalent to
or predicted maximum field water content the field capacity). ECs represents the salt content at (approximating field capacity), used to assess salt the point where soil profile drainage has essentially movement through the soil (usually predicted from ceased, and is determined using centrifuge or other 1:5 and soil properties). displacement methods. However, technique problems EC provides a measure of the content of salts in with wetting and extraction result in similar errors to 1:5 determining EC . The salinity at maximum field water a 1:5 soil water suspension, the most commonly se used method of analysis. EC, chloride (Cl) and pH content is used when estimating leaching fractions are usually measured together to provide additional and in solute movement studies and modelling as the information for interpretation. (Field and laboratory soil solution is assumed to be in equilibrium with the soil matrix. techniques for determining EC1:5 are described in Soil salinity page 60.) Table 7 illustrates the relative dilutions above field The ratio of 1:5 was established in response to water content for each of the EC measures. difficulties that arise when using the traditional Table 7. Relative dilution above maximum field water saturation extract mixing method with heavy content (field capacity) for three measures of soil salinity, EC , EC and EC . textured Australian soils (described below). EC1:5 is a 1:5 se s convenient laboratory and field technique. However, Measure Dilution above maximum field water it is not directly related to soil behaviour and plant content (upper drained limit) response because the ratio is far more dilute than is ECs 1 time at depth, equal to field capacity in normally found under field conditions and it surface soil is fixed irrespective of soil texture. EC1:5 results tend to ECse 2 to 3 times at depth, equal to saturated provide an underestimate of the electrical conductivity surface soil of sandy soils compared with clay soils. EC1:5 5 to more than 40 times, depending on soil Plants respond to salinity at water contents equal to texture or drier than saturation. ECse is the most dilute soil solution concentration that plants could be likely to Converting from EC to EC encounter and has been successfully used to relate 1:5 se plant response to soil salinity for a wide range of It is possible to provide mathematical relationships soil textures. This saturation water content, a well- between the EC measures based on water content accepted standard (USSL 1954), is used because it differences but, because the chemistry of solutions is the lowest reproducible soil:water ratio for which involving dissolution and precipitation and ion enough extract can be readily removed for analysis, exchange are profoundly affected by water content, and it relates in a predictable manner to field soil considerable errors can occur in relating the water contents and soil textures (Rhoades 1983). corresponding EC values.
30 Salinity management handbook However, as EC1:5 is the most convenient method for To derive ECse, the equation can be rearranged to: determining salinity in soils, techniques for converting Q EC = EC 1:5 ...... 6 to other measures of EC are required. Figure 25 shows se 1:5 Qse the relationships between EC1:5 and each of ECse and Q1:5 can be assessed as (500 + 6ADMC) for a 1:5 ECs. These conversions can be carried out using the SALFCALC component of the SALF software package, soil:water suspension (where ADMC is air dry moisture an easy-to-use calculator program for converting content expressed as kg/100 kg). Thus it is possible to between measures of salt content at different convert from EC1:5 to ECse if the ratio of water contents water contents, based on soil properties (refer to (Q1:5:Qse) is known. the appendix Useful software packages page 141). However, it is not this simple for a number of reasons
Detailed methods for converting between EC1:5 and (as discussed in detail in Shaw 1994): EC are provided in Shaw (1994) and summarised in se 1. Saturation water content has to be predicted from this section. other soil properties such as air dry moisture Figure 25. Figure to estimate the conversion factor between content and clay content.
EC1:5 and ECse based on clay content and EC1:5/ECse ratio 2. Soils contain slowly soluble salts, such as gypsum, (Shaw 1994). sodium carbonate and bicarbonate, and calcium carbonate. These salts are more soluble in dilute solutions, and their solubility depends on the composition of other salts present. For instance, gypsum is more soluble if sodium chloride is present and less soluble if calcium chloride is present. Hence the composition of salts will affect the electrical conductivity of the solution as a 5 1: whole. /EC se 3. EC1:5 is usually measured on the solution of soil:water suspensions after mixing and standing.
ratio of EC Where some clay remains in suspension, the charge
on the clay contributes to EC1:5. ECse is measured on extracts without any clay contribution. 4. Increasing dilution results in ion exchange with a preference for monovalent ions such as sodium on the exchange complex. This creates a sink for calcium, resulting in slightly enhanced solubility of calcium salts at greater dilutions compared with non-ion pair forming salts. 5. As a solution becomes more concentrated, To relate EC1:5 measurements to plant salt tolerance data, soil leaching and soil behaviour, it is necessary dissociated ions pair together forming neutral ion pairs such as CaSO o. Since these ion pairs to convert EC to EC (saturation extract). 4 1:5 se do not conduct electric current, the EC at high For pure solutions of salts that are totally soluble in concentrations of salts that form ion pairs is 1:5 soil:water suspensions, the EC of soil at saturation reduced. Thus the direct conversion of EC1:5 to ECse extract would be directly proportional to the EC of the may overestimate EC at high salinity levels. 1:5 suspension. se To accurately estimate ECse from EC1:5, both the ratio Expressed as a mass balance equation: of water contents and the composition of salts need
QseECse = Q1:5 EC1:5 ...... 5 to be known. The water content ratio can be estimated where from surrogate soil properties, which include clay content, ADMC, CEC, –33 kPa water content, –1 500 Q is water content equivalent to soil se kPa water content, and texture (as related to clay saturation (saturation percentage SP) content) (details in Shaw 1994 and applied in the ECse is electrical conductivity of salt solution SALFCALC software package). at the water content Q se The chemistry can be assessed from the concentration Q is water content at equivalent of 1:5 1:5 of chloride salts in proportion to total salt content. soil:water suspension Since the dominant anions in soil water extracts EC is electrical conductivity of salt solution - 2- 1:5 are Cl and SO4 (with smaller proportions of HCO3-, at 1:5 soil:water dilution. 2- - CO3 and NO3 ), and since chloride is often measured
Salinity management handbook 31 routinely with EC1:5, the proportional contribution of As a rule of thumb, 50% of soils will have an EC1:5/ chloride to the EC can be calculated. The ratio EC1:5/ ECse of between 1 and 2, 40% between 2 and 6, and ECCl provides an estimate of the very soluble and 10% greater than 6 (Shaw 1996). Texture groups and sparingly soluble salts present by converting the median clay contents are provided in Table 8 to allow chloride percentage of the 1:5 soil:water suspension approximate conversions.
(kg/100 kg soil) to an equivalent EC (dS/m). As ECCl (dS/m) can be closely approximated by 6.64 x %Cl1:5, this calculation can be readily made as: Leaching fraction An estimate of leaching fraction is important when EC EC considering the suitability of a soil for irrigation or for 1:5 = 1:5 ...... 7 determining the likely impact of land use change on ECCl Cl%*6.64 the amount of water moving below the root zone to the Table 8. Relationship between texture class and texture groundwater system. Measurement of leaching under grades and approximate clay contents of McDonald and field conditions presents large logistical problems Isbell (1990). and the use of deterministic solute models to predict leaching requires water application estimates, plant Texture Texture grades of McDonald Median clay class and Isbell (1990) content water use estimates and detailed description of soil (approx.) % hydraulic properties. Therefore, a simple empirical approach was developed by Shaw and Thorburn sand sand 5 (1985) to predict salt leaching for dryland soils and loamy sand loamy sand, clayey sand 7 which is also applicable to irrigation. This model sandy loam sandy loam 15 provides the basis for the SALFPREDICT model which silty loam loam, silty loam 25 is discussed in Soil salinity (page 60) and Useful clay loam clay loam, silty clay loam 32 software packages (page 141). light clay light clay, light medium clay 40 The estimate of leaching fraction under steady state medium clay medium clay 50 conditions is based on the concept that the mass flux heavy clay heavy clay 65 of solute applied to a soil profile will equal the mass flux of solute leaving the profile at steady state. For a
solute such as chloride that undergoes no chemical If chloride is expressed as ppm or mg/kg, the bottom transformation and negligible plant uptake, the line of the above equation becomes: relationship can be expressed:
EC1:5 EC1:5 ...... 8 ECi Dd = LF = = ...... 9 ECCl (Cl/10 000)*6.64 EC D d i
The concentration of very soluble salts will change where linearly with changes in water content (as modelled in i is input the mass balance equation at the start of this section). d is drainage below the root zone. However, the concentration of sparingly soluble salts that form saturated solutions at the water contents There are several methods available for estimating under discussion will not change linearly with changes leaching fraction under both steady state and non-steady state conditions. These methods are in water content. In these cases, ECse cannot be summarised in Table 9. accurately estimated from EC1:5 if a linear relationship is assumed. The proportion of the EC contributed by soluble salts must be known for reasonably accurate Long-term irrigation (steady state) conversions. Where soils have been under irrigation for some years These calculations can be carried out using SALFCALC. steady state conditions should exist. Under these Alternatively, an appropriate conversion factor from conditions the leaching fraction model (USSL 1954) will be valid. LF can be calculated from the previous EC1:5 to ECse can be determined from Figure 25 by reading a value from the curve which represents an equation: appropriate clay content and represents the EC1:5/ECse ECiw+r line. LF = ...... 10 ECs
32 Salinity management handbook Table 9. A summary of the methods and data required for Instead, the change in soil salinity which occurs estimating leaching fraction for different conditions. between two sampling times can be used. The model used in this situation is that of Rose et al. (1979). The Condition/ Field data Method model is most suited to slowly permeable soils with model long time periods required to reach equilibrium. The Long-term EC and amount of irrigation EC converted 1:5 data required for use of the model are soil salinity irrigation water, rainfall, EC1:5 at to ECs and - (steady bottom of the root zone 0.6 leaching profiles (preferably Cl ) at two sampling times, the - state–5 to 10 to 1.2 m. Maximum field fraction amount and salinity (Cl ) of irrigation water used, and years) USSL water content or surrogate calculated the maximum field water content of the soil. This final (1954) (SALFCALC) parameter is easily predicted from the equations of Short-term Cl of irrigation water. Deep drainage Shaw and Yule (1978) for most slowly permeable soils
irrigation Cl1:5 profiles taken at two and leaching (Thorburn & Gardner 1986). (non-steady times. Depth rainfall and fraction state) Rose irrigation. Maximum field calculated The equation of Rose et al. (1979) is: et al. (1979) soil water content or (SODICS) Thorburn et estimate surrogate soil D S D l t S = S + i i _ S 1 _ exp _ d . . 11 al. (1987) properties 2 1 ( D 1)( (( z ))) d l q Prior to Clay and CEC from 0 to 0.9 Leaching irrigation m, ESP at 0.9 m, annual fraction where Shaw and rainfall and irrigation, and predicted S , S are mean root zone salinities determined Thorburn EC irrigation from these 1 2 (1985a) parameters at two different times (SALFPREDICT) t is the time in years New As above, plus quantity (SALFPREDICT) Si is solute concentration of the irrigation irrigation and EC of past and future water water irrigation water, annual salinity rainfall Di is depth of infiltration Shaw and z is depth of root zone Thorburn (1985a) q is volumetric water content to which drainage will occur λ is a factor to account for soil salinity EC is the rainfall weighted input. EC is most readily iw+r s profile shape. determined from soil ECse or EC1:5 measurements The value of D is the only unknown in the equation (taken at the bottom of the root zone). As EC1:5 is a d and can be calculated from the model. It can be used less concentrated measurement than ECs, the EC1:5 to calculate LF and give the average root zone EC value value will have to be converted to ECs from the ratio of dilution. This procedure has been described in detail that will occur at that site at steady state. The model in the previous section and is shown in the examples can also indicate the time period when steady state following. conditions will be reached and how much soil salinity will increase (or possibly decrease) until that time. If Firstly, the EC to EC conversion factor is 1:5 se the final EC root zone value at steady state is too great determined. This factor depends on clay content and for the crop to be grown, irrigation management would salt composition. Secondly, EC is usually about 2.2 s have to be changed before that time. times more concentrated than ECse, so the EC1:5 to ECse Calculations are performed most easily using the conversion factor is multiplied by 2.2 to give the EC1:5 computer program SODICS of Thorburn et al. (1987). to ECs conversion factor. This is a rough approximation and depends on salt composition. Before using this model, readers would be best advised to refer to Rose et al. (1979) and Thorburn et Short-term irrigation al. (1987 and 1985) for further details and examples. As irrigation changes the salt balance, soil salinity Prior to irrigation will change (increase or decrease) after the commencement of irrigation until a new equilibrium To assess the suitability of land for irrigation, the is attained (steady state conditions). Until steady LF value that will occur under irrigation needs to be predicted. Shaw and Thorburn (1985a) and Shaw state conditions exist, ECs will not give an accurate indication of LF. (1996) developed a method for directly predicting the LF (PLF) that would occur under irrigation.
Salinity management handbook 33 The soil properties of dominant influence on soil On the basis of experience with heavy textured soils in leaching are clay content, clay mineralogy (CCR) the Lockyer Valley using variable salinity irrigation
(expressed as CEC/clay ratio, molec/kg of clay) and waters, and because the soil responses to salt vary ESP. As a result of the relationship between soil with physico-chemical properties, a non-linear properties, ESP and rainfall are specified for different adjustment was developed where the adjustment soil groups across a wide range of rainfalls. LF under decreases with the increasing salinity of the irrigation can then be calculated by substituting the applied water. The non-linear adjustment for salt depth of irrigation plus rainfall Di+r,for Dr. Because concentration is used in SALFPREDICT to predict a change in electrolyte concentration will result in a leaching fraction for irrigating with different salinity change in leaching for a given soil ESP, an adjustment waters. Thus the EC ratio component of the equation of the predicted leaching fraction is made. given above is adjusted as follows: 0.5 PLF is calculated from the general equation for each EC r iw+r _ soil group using the general form PLF = EC divided by LF = LF 2.65 1.35 ...... 15 r r f p ( ( EC ) ) 2.2 times EC where EC can be predicted utilising r se se soil properties information (Shaw 1996) giving the Accurate estimates require more detailed following equation: investigations of soil response to salinity and sodicity.
ECr
PLFr = 0.03 rainfall . . . . 12 2.2*10 a+b log ESP Root zone salinity ( ( )) Plants respond to salinity throughout the root zone, Exchangeable sodium percentage (ESP) of the soil so it is useful to be able to convert measurements at under irrigation can be calculated following the various depths in the root zone into a single number procedure discussed later in the section on soil that can be used when considering plant response. sodicity. The model SALFPREDICT has been developed Two measures of root zone salinity are commonly to simplify these calculations and is included on a CD used: average, and water uptake weighted. Both in the back cover of this book. require an estimate of root depth for the particular An assumption of the amount of irrigation water to plant species under consideration. be used in the future is required. If information on irrigation practice is not available, a value for Diw can Average root zone salinity be estimated from: Because plants respond to the integration of
Diw = 1 300 – Dr ...... 13 atmospheric and soil conditions, averaging the salinity for the root zone depth (average root zone The value of 1 300 mm is the 10-year average Diw + salinity) will provide a conservative measure of soil Dr in a survey of data from 10 Queensland irrigation areas, covering cotton to sugar cane. Variation of this salinity conditions for estimating plant response. figure will be required for supplemental irrigation on a Several studies (Devitt et al. 1984; Rhoades 1982; limited basis and for different climate regimes. Bernstein & Francois 1973) have shown average root zone salinity to provide an appropriate estimate of New irrigation water salinity root zone salinity for determining plant response to salinity. Shaw and Thorburn (1985a) found that the change in LF between a rainfall situation and irrigation Average root zone salinity is calculated from was closely related to the ratio of the weighted soil profile salinity data by summing the salinity salinity of the irrigation water and the rainfall in the measurements for a series of root zone depth future situation, and the rainfall salinity itself. The increments and dividing by the number of increments. relationship is: Water uptake weighted root zone salinity EC iw+r Many Australian soils have reduced soil porosity, LFf = LFp ...... 14 ECr hydraulic conductivity and water storage capacity with
depth, and increasing salinity with increasing depth. where Thus a measure of root zone salinity weighted for the f, p are future and past LF values. actual water uptake pattern of plants in the root zone would possibly provide a more realistic estimate of ECiw+r is the weighted average salinity of rainfall and irrigation water and is calculated from the equation to plant response than a measure that averages root calculate the conversion. That is, the equation above zone conditions. represents a special case where no irrigation water was used in the past management practice.
34 Salinity management handbook The weighted measure is based on the concepts that where water is more available to plants in the less saline i is number of the 0.1 m depth increment areas of the root zone and that water uptake by roots for which the calculation is currently is not uniform throughout the root zone. In fact, being performed the shape of the water uptake pattern with depth WF is weighting factor for the current depth varies considerably with frequency of rainfall and/or i increment irrigation. n is total number of depth increments (for Some general and specific approaches to water example, n = 9 for a root zone depth of uptake with depth have been used based on root 0.9 m). length density and more generic rooting patterns (for example, Hoffman and van Genutchen 1983). The Figure 26. Graphical representation of two measures of root approach is appropriate where subsoil salinities are zone salinity: average root zone salinity, and water uptake weighted root zone salinity. Weighting factors are given in high because roots cannot remove much water in Table 10 page 46. these situations. Shockley (1955) found that 40% of soil water extraction by plants occurred within the top quarter of the root zone depth, 30% in the second quarter depth, 20% in the third quarter depth and 10% in the fourth measured soil salinity quarter. This relationship has been widely used (for profile soil salinity example, Rhoades 1983), and is quite similar to that determined for cracking clay soils at Emerald under 10 to 14 day irrigation (Shaw & Yule 1978). Under conditions of frequent irrigation, higher proportions of soil water extraction are likely in the top 25% of the root zone. Hoffman and van Genutchen (1983) considered another exponential water uptake pattern. Their pattern probably places too much emphasis on the surface soil depths and underestimates the amount of water available to plants at lower depths in the root zone. In this handbook, a 40:30:20:10 proportional water uptake pattern for each quarter of the root zone has been adopted for both dryland conditions and irrigated conditions where some water stress will occur. Water uptake weighted root zone salinity probably provides a better representation of root zone salinity where subsoils are saline. This is typical of many less permeable soils in Australia since subsoil salinity indicates reduced wetting and thus limited water availability. Average root zone salinity and water uptake weighted root zone salinity are compared graphically in Figure 26. Using the generalised water uptake pattern of Shockley, weighting factors can be derived using the following regression equation (Shaw et al. 1987; based on data from Shockley 1955) for 0.1 m depth increments: The weighting factors for 0.1 m depth measurements determined using this regression equation for three i 0.6 WF +WF + ...WF )= (1.042 ) _ 0.00128) common root zone depths (0.6 m, 0.9 m and 1.2 m) S ( 1 2 i n . . 16 ( ) are shown in Table 10. These factors are applied to
actual ECse values to provide weighted values that represent the likely effect of the ECse values on a plant,
Salinity management handbook 35 based on the concentration of salt and the activity Converting leaching fraction to root zone of the plant’s roots at that depth. The weighted salinity ECse values are then summed down the root zone to provide the measure of water uptake weighted root To relate to plant salt tolerance for application in an zone salinity. In Table 11, the weighting factors are irrigation situation, leaching fraction can be converted presented for commonly used standard soil analysis to a water uptake weighted root zone ECse or an depths on the assumption that depths below 0.1 m average root zone ECse. Average root zone leaching represent the EC of the depth increments on either fraction or water uptake weighted root zone salinity side of the nominated depth as well as the nominated can also be calculated from leaching fraction to relate depth. As an example, the two measures are derived to plant salt tolerance using the relationships in for a black earth soil at Emerald in Table 12. Figure 27. These are derived from Rhoades (1983) as explained by Shaw et al. (1987), where the appropriate Table 10. Water uptake pattern weighting factors for 0.1 regression equations are given. m depth increments for three common root zone depths, derived using equation 16 (Shaw et al. 1987). Smith and Hancock (1986) derived a neater mathematical solution to relate water uptake Soil depth Weighting factor for each 0.1 m increment weighted root zone salinity to the leaching fraction at increment where root zone depth is the bottom of the root zone: (m) 0.6 m 0.9 m 1.2 m EC In LF EC = i ...... 17 0–0.1 0.35 0.27 0.23 wuw LF – 1 0.1–0.2 0.18 0.14 0.12
0.2–0.3 0.15 0.11 0.10 where ECi is EC of input water to soil surface. 0.3–0.4 0.13 0.10 0.08 Table 12. Average and water uptake weighted root zone 0.4–0.5 0.11 0.09 0.07 salinity measures for a black earth soil from Emerald (root 0.5–0.6 0.08 0.08 0.07 zone depth of 0.9 m). 0.6–0.7 0.08 0.07 Soil depth Analysed ECse Water Weighted 0.7–0.8 0.07 0.06 increment (dS/m) uptake ECse (EC x 0.8–0.9 0.06 0.06 (m) weighting weighting factor (refer factor) 0.9–1.0 0.06 Table 10) 1.0–1.1 0.05 0–0.1 0.4 0.27 0.23 1.1–1.2 0.03 0.1–0.2 0.4 0.14 0.12 Sum 1.0 1.0 1.0 0.2–0.3 0.4 0.11 0.10 0.3–0.4 0.5 0.10 0.08 Table 11. Water uptake pattern weighting factors for 0.4–0.5 0.7 0.09 0.07 standard survey depths of three common root zone depths, derived using equation 16 (Shaw et al. 1987). 0.5–0.6 1.1 0.08 0.07 0.6–0.7 1.9 0.08 0.07 Weighting factor for each standard depth 0.7–0.8 3.2 0.07 0.06 Soil depth increment where root zone depth is (m) 0.8–0.9 4.2 0.06 0.06 0.6 m 0.9 m 1.2 m average root water 0–0.1 0.35 0.27 0.23 zone: uptake weighted 0.1–0.2 (mean) = 1.42 root zone: 0.2–0.3 0.46 0.35 0.30 0.3–0.4 (sum) = 1.03 0.4–0.5 0.5–0.6 0.19 0.25 0.18 This equation is very similar to the dashed line in 0.6–0.7 Figure 27. If the bottom of the root zone leaching 0.7–0.8 fraction is known or predicted and the salinity of the 0.8–0.9 0.13 0.18 input water (rainfall plus irrigation) is known, Figure 27 can be used to calculate root zone salinity and to 0.9–1.0 evaluate plant salt tolerance data and irrigation water 1.0–1.1 quality. 1.1–1.2 0.08 Sum 1.0 1.0 1.0
36 Salinity management handbook The ECse under irrigation can be varied using the new Soils with high montmorillonite clay content (those leaching fraction instead of the assumed leaching that swell and shrink) can tolerate higher ESP than fraction of 0.15 to relate to water quality criteria (see clay soils with limited capacity to swell and shrink Irrigation page 81). (Shaw et al. 1994). This is because the restructuring of the soil during swelling and shrinking overcomes Since LF is based on EC (field capacity), permissible s some of the problems caused by dispersed clay. irrigation water quality for a specified leaching fraction However, wet dispersed soils (regardless of clay is calculated as: content) will have reduced infiltration and be prone to EC = 2.2 (EC LF ) ...... 18 iw se increased runoff and erosion. where the terms EC and LF are either average or se Magnesium associated with sodium has commonly water uptake weighted. been thought to aid soil dispersibility (for example, Figure 27. Relationships for assessing average root zone Emerson and Bakker 1973). There is considerable leaching fraction or water uptake weighted root zone evidence that this effect is much more applicable to leaching fraction, based on the 0.4, 0.3, 0.2, 0.1 water illite soils than montmorillonite soils, although further uptake pattern with depth of Rhoades (1983) (Shaw et al. research is required. Some researchers propose 1987). that low exchangeable Ca:Mg ratios in conjunction 1.0 with ESP indicate enhanced dispersion. There is still debate about the role of Mg. The alternative view is 0.9 that Ca causes flocculation, Na causes dispersion, 0.8 and Mg acts in a fairly neutral manner and, in the absence of Ca, can increase the effects of Na to some 0.7 extent. 0.6 High salt concentration will flocculate the clay and
0.5 maintain aggregation and hydraulic conductivity. The actual thresholds at which this occurs vary with clay 0.4 type and ESP. (This is discussed in further detail in Irrigation page 81.) 0.3 0.2 ESP 0.1 ESP is determined by routine CEC and exchangeable
0 cation methodologies as outlined by Bruce and
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Rayment (1982) and Rayment and Higginson (1992). Soluble cations are removed via a washing step and the exchangeable cations (which are subsequently analysed) are displaced by ammonium ions (at Sodicity in soils and waters a nominated pH). The total CEC is determined by displacing and analysing the ammonium ions. The two most common measures of sodicity are: • exchangeable sodium percentage (ESP), which is ESP is calculated as follows: the proportion of sodium adsorbed onto the clay 100 Na+ mineral surfaces as a proportion of the total cation ESP = ...... 19 exchange capacity CEC
• sodium adsorption ratio (SAR), which is the relative In the absence of CEC data, the sum of the concentration of sodium to calcium and magnesium concentrations of the cations Na+, Ca2+, Mg2+ and K+ in the soil solution or (irrigation) water. can be used as an approximation of CEC except: ESP is a measure of soil sodicity and SAR is a measure • in acid soils (unless exchange acidity has been of soil solution or water sodicity. The relationship determined, see Bruce and Rayment 1982), where between the SAR of the soil solution at saturation the summation of cation concentrations will and the ESP is given in USSL (1954) and is generally provide an overestimate of ESP applicable to a wide range of soils. • in alkaline soils where Tucker’s solution at pH 8.4 (Rayment and Higginson 1992) has not been used to extract cations, since sparingly soluble calcium salts will inflate the value for Ca2+ concentration value and hence provide an underestimate of ESP.
Salinity management handbook 37 In some variable charge soils (usually acid soils), the summation of the concentrations of the four cations may provide an overestimate of CEC, due to pH-dependent charge, and ESP calculated using this CEC may be an underestimate. A more appropriate measure of CEC is necessary for these soils.
SAR Sodium adsorption ratio (SAR) is calculated as follows:
Na+ SAR = ...... 20 0.5 (0.5(Ca2+ + Mg2+)) where ionic concentrations are in meq/L, determined from the soluble ions in the saturation extract. (If units of mmolec/L are used, the calculation is the same as equation 20 above. However, if units of mmole/L are used, the concentration of calcium and magnesium ions should not be halved. Converting between these units is illustrated in Useful conversions and relationships page 158.)
38 Salinity management handbook Chapter 6 — Landscape characteristics and salinity mapping Landform feature identification less permeable sandstones and mudstones at fairly shallow depths (Figure 28a). Basalt which Geological features and past patterns of weathering is fractured, columnar or vesicular forms suitable make some landforms more hydrologically sensitive groundwater recharge areas and transmission zones. and susceptible to salting than others. The important Basalt gravels in old valley infill areas also form feature of sensitive landforms is the presence of aquifers which readily transport water. some restriction to groundwater flow that causes the The restriction to downward water movement is watertable to rise to near the soil surface, resulting provided by the underlying material which, being in a discharge area with evaporative concentration of less permeable than the overlying basalt, restricts salts. Watertable salting commonly occurs in positions continued downward water movement. In addition, in the landform indicated as potential discharge layering within the basalt and bole (previously areas in the diagrams accompanying the following weathered) layers provides regions of variable descriptions (Figure 28). permeabilities which can contribute to salting. Hydrologically sensitive landscapes often show Seepages or shallow watertables occur at the evidence of past seepages or shallow watertables. If interface areas. The basalt form is characterised by development in these types of landscapes changes both seepage and watertable salting with source the hydrological balance, salting may occur as a waters (usually of low salinities) concentrated by result. evaporation. This form is evident on the eastern Landforms occur in patterns in regions and can be Darling Downs, central Queensland and on lateritised compared readily within a region. Once identified, basalts in the Rockhampton and Kingaroy areas. they are useful for indicating sensitive areas of the landscape which can be further investigated. Figure 28a. Basalt form Landform features will also determine which management strategies may be effective (discussed in R restriction Integrated management strategies page 93). seepage water flow The advantage of using landforms to diagnose R susceptibility is that landforms can be readily observed without undertaking detailed (and basalt sometimes expensive) site investigations.
Sources of information sandstone/mudstone • Inspecting the property and other properties in the catchment is the most direct way of identifying landform features. • In some cases, it may be easier to identify Catena form landforms on aerial photographs or topographical This form occurs where soil forming processes and and geological maps. (Features on geological maps wetness have resulted in a change in soil properties relevant to identifying landforms at risk of salinity down a slope. The form comprises shallow soils in are described in Geology page 42.) upslope positions overlying weathered parent material • Landforms in some areas may have already been with soils gradually becoming deeper and heavier identified and discussed in land or soil survey textured downslope extending onto flat heavy clay reports. alluvial areas (Figure 28b). Sodicity may be high at the base of the slope, further Landform feature descriptions restricting permeability. More recent infills of clays at the bottom of the slope can restrict outflow. Soils Basalt form at break-of-slope positions tend to be saline at some The most common landform associated with salinity depth, indicating a past history of high watertables. in Queensland, this landform comprises both Restricted drainage results in salt accumulation. recent and highly weathered basalt flows overlying
Salinity management handbook 39 The change in hydraulic gradient creates a similar effect Catchment restriction—roadway to a barrier to water movement. Salting results from infiltration of water into the soils and lateral movement This type of restriction occurs on heavy clay areas through the weathered parent material or through more where roads and stock routes across alluvia have permeable soil horizons. Discharge occurs in the lower compacted the soils, particularly in wet periods. slope or break-of-slope positions where the heavier This reduces the water transmission properties of clays or geologic features (for instance, dykes) restrict the soils sufficiently to raise watertables and cause water movement. In some situations, the weathered salting upslope of the road (Figure 28d). This form is parent material can act as a confined aquifer contained represented in the Lockyer Valley, Darling Downs and by the less permeable soils above and the less central Queensland. weathered rock below. Figure 28d. Catchment restriction—roadway This form is evident in the Boonah area in south-east Queensland, on the Burdekin River right bank and in R many other small occurrences. R road Figure 28b. Catena form
R basement rock
Catchment restriction—natural basement rock Rock bars or resistant sediments can restrict water flow in valley floors or where existing aquifers thin out. The catchment throat is often narrowed in Alluvial fan width and/or depth. Discharge areas develop in the region upslope of the restriction (Figure 28e). This is This form occurs where the coarser sediments of an particularly common in the Lockyer Valley, Boonah old alluvial fan have been subsequently buried or and Rockhampton areas. The McDonnell ranges in partially buried by clays (Figure 28c). Subsurface central Australia are a classic case of this form. water flowing from upslope areas or old stream channels enters the alluvia of the former land surface Figure 28e. Catchment restriction—natural which acts as an aquifer for water transmission. Discharge areas occur where heavy clays, more recent R alluvia, or finer sediments are deposited over the coarser materials at the margins of the alluvial fans. The form is represented in central Queensland on Tertiary sediments, on the eastern Darling Downs on basalt, as alluvium associated with granites near Mareeba, and as old fans from stream breakouts in the Sarina area. Alluvial valley Figure 28c. Alluvial fan This is a particular form of catchment restriction where a geologic restriction to water flow out of a catchment R results in the deposition of alluvium (Figure 28f). These valleys are usually associated with a very low hydraulic gradient. This form is evident in a number of alluvial valleys in Queensland where large historic recent alluvium salt loads have accumulated in down-valley areas in the unsaturated zone at the interface between shallow watertables and tree roots. Remobilisation of this
basement rock old alluvium historic salt causes the observed salting. Valleys with no incised drainage line are particularly prone to this type of salting process.
40 Salinity management handbook Water quality modelling in the Lockyer, Callide and Dykes Dee valleys indicates that in these systems the major Geologic dykes can form areas of variable process of salt accumulation is the extraction of water permeability in the landscape. Where less fractured from capillary fringes of aquifers by deep-rooted or weathered dykes occur across the direction of vegetation. Accumulated salts are leached back into slope, water movement downslope is interrupted and the aquifer system, increasing salinity. Additional incipient or permanent salting areas develop (Figure geomorphic and geological restrictions to water flow 28h). This is most evident in the Burdekin and can intensify these effects by raising groundwater Mareeba areas in north Queensland on granites, and levels. In these valleys, salinity gradients increase also in central Queensland. with distance from the head of the valley. Where heavy clay alluvium has been deposited on top Figure 28h. Dykes of permeable materials, salting may extend over large areas due to the upward movement of water under R hydraulic pressure. This particularly occurs in granitic landscapes where the high proportion of sodium released on weathering results in sodic clays of low permeability in valley floors. Upward flow through this confining layer contributes to salting by evaporative concentration.
Figure 28f. Alluvial valley Stratigraphic form R Variable permeabilities in sedimentary rock layers can act as preferential flow paths or impermeable areas under increased water regimes. In this situation, small seepages and salted areas appear on hillslopes alluvium in response to variations in the permeability of different rock layers (Figure 28i). This form is evident
basement rock in the Lockyer Valley and other areas on a variety of sedimentary rock types. Lateritic and ironstone cappings are variations of this form.
Figure 28i. Stratigraphic form Confluence of streams At the junction of a minor stream with a major stream, R R R the reduction in flow velocity and resultant deposition of suspended particles at the junction results in a greater proportion of clay in the sediments at this point with lower lateral permeability (Figure 28g). This occurs particularly in the smaller stream immediately upstream of the junction. This form is evident in the Boonah area and, in conjunction with the alluvial valley form, in the Callide Valley as well as in other areas.
Figure 28g. Confluence of streams Geological faulting Faulting can operate in a similar manner to dykes or alternatively can provide preferential upward R flow paths for water (Figure 28j). The mound springs R around the southern fringes of Lake Eyre and the seepage in the Yelarbon desert region are classic R cases of the latter form of geological faulting.
Salinity management handbook 41 Figure 28j. Geological faulting Geology Most dissolved salts occurring in natural waters R originate from the combination of salts in rainfall and weathering of rocks near the land surface. High salinities occur in many of the fine-grained sedimentary rocks (mudstone and shales). Also, and more importantly, geological structures can Dams control water movement in landscapes. By identifying A dam can contribute to salting both upstream and underlying geological formations, information is downstream of the dam itself (Figure 28k). The dam obtained which will facilitate the identification of also acts as a hydraulic barrier to groundwater flow. landform features in the region (see the previous Upstream salting results from reduced hydraulic section Landform feature identification page 39). gradient of downslope flow caused by the raised water level of the dam. Downstream salting results Sources of information from leakage of water, usually above a shallow, • Regional geological maps are available. However, less permeable subsoil layer. This form is relatively the boundaries of geological formations on these common. 1:250 000 maps may not be accurate enough to Figure 28k. Dams pinpoint salinity outbreaks, depending on the source of data. For this reason, these maps are R valuable for a broad assessment of geological
bank formations occurring in the area, providing a guide pond only in specific local areas. leakage • More detailed geological information may be available, particularly if properties in the area have been subject to detailed mineral investigations at some stage. If specific geological surveys have watertable level rising been carried out, these would be available on open file from the appropriate department. Previous investigations on the property, perhaps held by Lakes (groundwater terminus) former land owners, may also be useful. • Geological information relevant to the area under Regions where surface water and groundwater investigation may be listed with Queensland terminate with limited outflow and hence flushing Spatial Information Directory (QSID), a are generally salted due to evaporative concentration computerised directory of land-related information. (Figure 28l). Lake Eyre and Lake Buchanan (near Jericho) in Queensland are two classic natural The geology of source rocks can often be determined cases of this form. The salting in the centre of Wolfe from dissolved salts in the groundwater. Interpreting Creek Crater, a meteorite crater in northern Western groundwater analyses is covered in Water chemistry Australia, is due to long-term accumulation of salts and salt sources indentification (page 73). from rainfall and weathering in an area of restricted drainage. The playa lakes of southern, western and Interpretation inland Australia are natural occurrences of salt lakes Hydrologic features and landforms commonly at that expand in response to land development. risk of watertable salting can be identified using Figure 28l. Lakes (groundwater terminus) readily available topographic and geological maps. Codes which appear on geological maps swamp or lake that may become saline are listed and described in Table 13 as an aid to interpreting maps. General interpretation guidelines for identifying hydrologic units within a landscape and landscapes at risk of watertable rise and salting are provided in Table 14. More information about landforms commonly at risk (such as basalt forms and constricted catchments) is provided in Landform feature identification (page 39).
42 Salinity management handbook Table 13. Common descriptive codes appearing on geological maps.
Geologic time period General Description codes Quaternary units (0–2 myr before Q undifferentiated Quaternary sediment present) Qa alluvium Qb beach ridges Qc scree and gravel ± silcrete Qd coastal/inland dunes Ql lacustrine sediments or limestone Qm mud flats Qr sandy red earth ± gravel Qs soil and/or silcrete ± residual sand and gravel Tertiary units (2–7 myr before present) T/Ts undifferentiated Tertiary sediments Tb basalt Tf ferricrete Tl laterite Cainozoic units (0–65 myr before Cz undifferentiated Cainozoic sediments present) Cza alluvial and/or deltaic sediments Czb basalt Czd coastal/inland dunes Cze estuarine sediments Czg unconsolidated sand and gravel Czl laterite Czs colluvial sands and silts ± duricrust Czy silicified quartz sand (‘billy’)
Landscape salinity mapping in the soil from a primary electric current in a coil held above the soil surface. The strength of the magnetic The mass and extent of salt in the landscape can be field is proportional to the electrical conductance of estimated and mapped using a number of remote the soil as measured by secondary current induced sensing and contact and non-contact ground-based in a receiver coil. The spacing of the emitter and geophysical methods. Using these methods, areas receiver coils determines the depth of the reading. of potential salinity hazard and salt loads likely to The depth response function is significantly more be mobilised under a wetter equilibrium can be responsive at the soil surface. The advantages of using identified. electromagnetic induction instruments are being able Commonly used remote sensing methods include to obtain continuous readings and the lack of soil aerial photography, LANDSAT, Thematic Mapping contact. (TM), airborne multi-spectral scanner (MSS), and Three instruments developed by Geonics Inc. of airborne geophysics. These methods are listed and Canada are commonly used (Table 17): their applications, key strengths, data type and cost- • EM‑38, with sensing depth to approximately 1.5 m, effectiveness are discussed in Table 15 (page 45). suitable for relating surface soil salinity to plant Ground-based geophysical methods commonly used growth for salinity and shallow groundwater investigations • EM‑31, with sensing depth to approximately 6 are listed and discussed in Table 16 (page 46). These m, more suitable for landscape salt and salting include electromagnetic induction instruments processes as well as providing a useful indication (discussed in more detail following), magnetics, of surface soil salinity radiometrics and seismic refraction. • EM‑34–3, with three coil spacings giving a Electromagnetic induction instruments facilitate maximum sensing depth of up to 60 m, useful a rapid assessment of amount and extent of soil for investigating landscape salt loads at deeper salinity. These instruments induce a magnetic field depths.
Salinity management handbook 43 Table 14. Generalised interpretation of shallow groundwater and saline hazard areas from maps using geomorphic and geological features.
Critical areas commonly requiring identification Landform commonly at risk Recharge areas Discharge areas Salt sources Basalt landforms Constricted catchments Geomorphological indicators Geomorphological indicators • elevated landforms • toeslopes • deeply weathered • weathered and/or • catchments with (ridges, ranges, • permanent streams landscapes dissected basalt narrow, laterally plateaus and upper • inland drainage caps on hills and restricted outflow slopes) • permanent plateaus waterholes, lakes systems • topographic highs at • dunes and swamps • coastal salt • margins of catchment outflow • beach ridges marshes elevated, red soil • broad, flat catchments • playa lakes landscapes • saline scalds with poorly incised • areas of poorly drainage incised drainage Geological indicators Geological indicators • rock outcrops • clay alluvia in • fine-grained • margins of Tertiary • just upstream of in elevated broad, flat valleys sediments of basalts (Tb, ‘pinched out’ areas landscapes— (Qa, Qc, Ql, Qs, marine origin Czb) and older, in broad Quaternary particularly basalt, Cza, Czs) • deeply weathered deeply weathered alluvium (Qa) sandstones and • estuarine or lateritised rocks basalts in elevated • broad areas of limestone sediments and landscape Cainozoic sediments • estuarine deposits positions • deeply weathered adjacent low lying (Cze) (Czs) as above intrusive rocks— areas (Cze) • margins of • stringers of sediment particularly granite • coastal mud flats lateritised rocks in • margins of basalts (Qm) along drainage lines and granodiorite in upper landscape upper landscape with restricted linear • strongly jointed or positions • carbonaceous positions (Ql, Tl, extent fractured rocks sediments (such as Czl) • coastal mud flats coal and • outcrop of basement • steeply dipping (Qm) carbonaceous (deeper) rocks at or sedimentary strata • peat deposits mudstones, near the land surface along drainage lines • lateritised rocks • playa and sabkha siltstones and (Ql, Tl, Czl) sediments (Qs) shale) • sand and gravel • playa and sabkha units (Qa, Qb, Qd, sediments (Qs) Qr, Ts, Czg, Czs)
Note: Source data for geomorphological indicators can be obtained from topographic maps and aerial photographs. Source data for geological indicators can be obtained from 1:250 000 geological maps and special purpose maps (for example, regolith maps, mineral exploration maps).
44 Salinity management handbook Table 15. Remote sensing methods commonly used for assessing shallow groundwater and salinity hazard. (Note: Prices quoted are indicative only at the time of printing. Actual costs will depend on availability of the equipment and the size and scope of the survey.)
Methods Application and Data type, Cost-effectiveness Comments key strengths information issues Aerial • provides information • hard copy • cheap as archival Aerial photographs photography on soils, vegetation • may be digitised data are one of the most patterns, landform useful initial data (black & white, • generally not rectified • expensive to colour) features, land use sources for any • digital capture capture data • suitable for farm and investigation available in future (suitable but catchment planning, very costly for maintaining site history • can be scanned monitoring if • high resolution, specific areas are archival data readily required) available LANDSAT Thematic • provides information on • digital raster data • moderate setup TM data have been Mapper (TM) or vegetation • 30 m per pixel (10 m cost, very cheap readily available in SPOT patterns, landforms and SPOT panchromatic) unit cost (approx. Australia since the geological structure, $0.05/ha) mid 1980s and are • readily integrated with land resources and still the most reliable digital topography and • data are multi-use land use satellite-based data geophysical data sets depending on • suitable for small processing used for land management • needs ground truthing catchments to regional use scale applications • needs specialist processing and • suitable for resource interpretation assessment, planning, validating models and monitoring • readily available, and archival data available Airborne multi- • provides information • digital raster data • moderate setup Application in spectral scanner on soil and vegetation • approx. 2 m per pixel, cost (approx. $10 Queensland (MSS) patterns and land use large data set 000) has been limited • large number of bands, • needs calibration (for • cheap unit cost including thermal infra- monitoring) (approx. 0.15/ha) red • generally not rectified • cost depends • suitable for monitoring on availability of • difficulties joining instrument • suitable for farm to (suturing) data from catchment scale multiple flight paths applications • needs ground truthing • rapid data capture • needs specialist interpretation Airborne • provides information • digital raster data • high setup cost Airborne geophysics geophysics on geological • readily linked with (>$50 000) due to has been a structure, rock types other data sets need for specialist traditional tool of 1. Electromagnetic (by inference), salt contractor and the mining industry. • approximately 70 m per induction accumulation, historic processing Its application to pixel 2. Magnetics and groundwater flow (by • cheap unit cost salinity studies in • needs appropriate radiometrics inference) (approx. $5/ha) Australia has had ground truthing mixed success, but • can provide depth • appropriate for • needs specialist ongoing refinements information major projects on interpretation (may to equipment, • suitable for catchment high-value land (i.e. not necessarily interpretive management and irrigation areas or map salt, provides processes and processes, shire and dams) little indication data manipulation regional planning, of hydrological • cost could be techniques are major projects importance of shared if data are showing promise (irrigation/dams) structures) of interest to other • rapid data capture clients (mining, environmental)
Salinity management handbook 45 Table 16. Ground-based geophysical methods commonly used for salinity and shallow groundwater investigations. (Note: Prices quoted are indicative only at the time of printing. Actual costs will depend on availability of the equipment and the size and scope of the survey.)
Methods Description Application and Limitations Cost-effectiveness Comments key strengths Electromagnetic • coil spacing 1 m • rapid site • shallow depth • instrument • commonly used induction (EMI)— • effective depth assessment penetration costs approx. to assess tree EM 38 1.5 m • useful for • readings $8 000 planting sites • measures surveying and are strongly • survey costs • also used in the apparent monitoring small influenced by approx. $10/ cropping areas conductivity sites for salinity in soil properties, ha depending to determine of the ground the root zone particularly on sampling salinity effects based on the • suitable for soil moisture and intensity in the root zone strength of salinity surveys iron oxides • does not • very useful as a secondary • monitoring use require an extension magnetic field limited to large specialist tool for induced in the differences operator landholders ground from a • field calibration and landcare primary field desirable groups emitted by the instrument Electromagnetic • coil spacing • rapid site • readings are • instrument • commonly used induction 3.7 m assessment affected by clay costs approx. for site survey (EMI)—EM 31 • effective depth • useful for site content and $23 000 and regional 6 m and catchment soil moisture • survey costs reconnaissance • measures reconnaissance • awkward to approx. $10/ • may be used for the apparent • suitable for use in heavily ha depending depth profiling conductivity mapping soil timbered areas on sampling (2 depths) of the ground salinity, ground- • field calibration intensity • mobile surveys based on the water contaminant desirable • can be offer benefits of strength of plumes and mounted on a larger data sets a secondary geological vehicle-drawn and greater magnetic field variation ‘plastic’ trailer accuracy induced in the • can be used to for mobile • very useful as ground from a locate gravel, surveys an extension primary field buried drums, • does not tool for emitted by the pipes and other require landholders instrument objects specialist and landcare operator, groups may require specialist interpretation of results Electromagnetic • coil spacing • rapid site • requires two • instrument • commonly used induction 10/20/40 m assessment operators costs approx. for site surveys (EMI)—EM 34–3 • effective depth • useful for regional • results can $17 000 and regional 15/30/60 m reconnaissance be strongly • survey costs reconnaissance • measures and depth profiling influenced approx. $20/ • may be used for the apparent • suitable for by depth to ha depending depth profiling conductivity mapping bedrock, type on sampling (3 depths) of the ground weathering profiles of rock and intensity based on the and salinity, deep degree of • does not strength of groundwater fracturing require a secondary contaminant specialist magnetic field plumes, operator, but induced in the groundwater does require ground from a prospecting and specialist primary field vertical geological interpretation emitted by the anomalies of results instrument
46 Salinity management handbook Methods Description Application and Limitations Cost-effectiveness Comments key strengths Magnetics • measures • single person • not capable of • instrument cost • not commonly the earth’s carry-pack determining the exceeds $20 used for salinity magnetic field • rapid hydrological 000 investigations reconnaissance effect of • surveys costs • could have geological approx. $10/ greater • good for structures determining ha depending application in geological on sampling areas of strong structures if intensity geological minerals are • does not or structural magnetic or require control contrast specialist in magnetism interpretation of results Radiometrics • measures the • hand-held • best only • instrument cost • not commonly radioactive instrument as a tool to exceeds $15 used for salinity isotopes of • rapid help interpret 000 • has a high potassium (K), reconnaissance geological/soil • does not potential for uranium (U) units require use in soil and thorium • radios of three radioactive • measurements specialist mapping (Th), and total do not relate operator, but isotope counts isotopes (K, U, Th) provide directly to does require • ratios of these information for conductivity or specialist isotopes constructing salinity interpretation indicate pseudo-soil/ of results the types geological maps of minerals present in the rocks and soil Seismic • differentiates • site surveys • requires at • instrument cost • not commonly refraction horizontal • good for least two exceeds $25 used for salinity strata by timing determining the operators 000 investigations the reflection of relative thickness • field set-up and • requires skilled • generally used seismic shock of strata operation are operator, for groundwater waves; denser • may be used slow particularly if prospecting rocks (e.g. fresh explosives are basalt) return to identify • not useful in watertables moderately to used to initiate high velocity shock waves waves; less steeply dipping dense strata strata or in • specialist (e.g. weathered rocks of strong interpretation sandstone) structural of results is return low control essential velocity waves
Table 17. Operational parameters of EM instruments in common use.
Intercoil Operating Operating Optimum depth penetration spacing (m) frequency (kHz) Vertical Horizontal dipole (m) dipole (m) EM 38 1.0 14.6 1.5 0.75 EM 31 3.66 9.8 6 3 EM 34–3 10 6.4 15 7.5 20 1.6 30 15 40 0.4 60 30
Salinity management handbook 47 Table 18. Typical values for EM 31 readings and their likely significance. Note: This table applies to typical soils and landscapes and not to creeks, dykes, roads or other anomalies in the landscape.
Typical EM 31 Likely material Likely clay Likely EC1:5 Comment reading (mS/m) content (%) of subsoil (dS/m) 10–20 Coarse sand < 10 < 0.05 recharge area, well-leached 20–40 Earths < 20 ≤ 0.15 recharge area, leached 50–80 Light clays up to 40 ≤ 0.25 recharge area, leached and permeable 80–130 Heavy clays—sodic subsoils 45–60 < 1.2 transmission area, ‘normal’ slowly permeable soils with subsoil salt 80–120 Heavy clays—non-sodic, 40–80 < 0.6 low recharge, ‘normal’ slowly permeable basalt in origin soils 130–200 Surface salt and low salinity variable 3–8 surface discharge area, may give a lower reading groundwater 0.5–1.5 than expected due to thin depth of surface subsoils salt 200–300+ Surface salt and high salinity variable 4–10 surface discharge area with higher subsoil salt groundwater 1.5–3 subsoils content
Interpretation of EM 31 readings Table 19. Classes of salt-affected land (adapted from Murray–Darling Basin Commission 1993). Note: ‘Watertable Readings for EM instruments are given in mS/m, 100 salting’ refers exclusively to the process of shallow times greater than the commonly accepted unit of watertable-related salinity; ‘Land’ refers to land systems dS/m for soil analyses. While these readings can be (recurrent patterns of geology, soils and vegetation) and readily converted, the EM readings are of the bulk soil associated surface and groundwater systems. at the given water content and will not directly relate to the results of laboratory soil analyses. Table 18 Class Description provides typical indicative values for EM‑31 readings Not at risk Land not predisposed to watertable salting based on field experience. regardless of land use or management EM instruments are sensitive to clay content and Stable Land predisposed to watertable salting but mineralogy, soil water content, and the depth of unlikely to become saline under existing land use or management bands of more conductive material in the ground. Some soils, for example ‘brigalow’ clay soils, have At risk Land predisposed to watertable salting which is likely to become saline under high salinity due to their very low deep drainage existing land use or management rates and do not as such indicate discharge areas. Slightly Land showing a reduction in non salt- There is considerable information available in affected tolerant plant vigour, some salt-tolerant the literature about the use of electromagnetic plants, seasonally or permanently shallow induction instruments to quantify salinity in different watertable, and perhaps small bare areas profile layers and the effects of other factors on the Moderately Land showing a significant loss of non readings. Ground truthing by taking soil samples is affected salt-tolerant plants, salt-tolerant plants recommended for verifying EM readings, particularly if are common, seasonally or permanently soils change across the landscape. shallow watertable, bare areas up to about 5 m2 in size, some erosion present Severel Land showing an absence of non salt- Landscape salinity hazard affected tolerant plants, permanently shallow watertable, large bare areas which are often classification badly eroded There are a number of schemes for classifying land according to its salinity status. The guidelines While it is difficult to estimate severity by any developed by the Dryland Salinity working group of universally applicable objective criteria, these classes the Murray–Darling Basin Commission (1993) are used offer a framework to describe what is happening or here. This classification scheme (Table 19) evaluates what may be expected to happen in an area. By using land on the basis of the current degree of salting standard terms such as these, salt-affected areas can as well as the degree of salinity risk under changed be mapped and described in different regions using land use or land management conditions (based on comparable criteria. watertable salting).
48 Salinity management handbook Chapter 7 — Vegetation
Table 20. Plant species and communities that can indicate Plant communities as salinity features of interest in salinity investigations. indicators Species or community Indicates Certain species are commonly found on salt-affected soils and can be useful for identifying salt outbreaks. Black tea tree (Melaleuca shallow groundwater— Where plant species are identified that are salt- bracteata) potential discharge area Tea tree generally tolerant or that compete more effectively under saline conditions, salinity may be occurring at the Melaleuca bracteata saline soil Melaleuca nodosa site. Where species that are not salt-tolerant are Brigalow (Acacia present in surrounding areas but are absent from a harpophylla) location, this may also indicate soil salting. Further Melaleuca spp. generally poor drainage—potential site investigations should be undertaken to determine Luxuriant grass and tree discharge area or stream whether salinity is in fact occurring, and to what growth boundary extent. Softwood scrub recharge areas Angophora sp. Cypress pine Sources of information Silver-leaved ironbark • Other texts for identifying indicator species are Narrow-leaved ironbark listed in the appendix Salinity publications for further reference (page 145). There is little published information relating trees and watertable depths. In areas in the Callide Valley where Native trees and shrubs the watertable was 6 m below the soil surface under Tea tree (Melaleuca sp.) is commonly associated with native vegetation, salting occurred after the vegetation many watertable salting occurrences in south-east was cleared (Hughes 1982a). In the Clermont area, and central Queensland; black tea tree (Melaleuca watertable salting occurred in areas cleared of stands bracteata) particularly so. Historical data and current of black tea tree where the watertable was at a depth presence of tea tree indicate water levels were of 5 m to 6 m prior to clearing (Hughes 1982b). shallow prior to clearing in most areas now affected by Plants and plant communities which often indicate watertable salting. recharge and discharge areas are listed in Table 20. Some small areas may have perched watertables Table 21 overleaf lists species that are useful that are local and unconnected with regional indicators of local soil conditions in the lower groundwaters. Perched watertables often support a Burdekin River–Elliott River area in north Queensland. tea tree understorey beneath eucalypt forest, whereas These species are quite widely distributed in permanently shallow regional groundwater levels Queensland. Poplar box (Eucalyptus populnea) and usually support pure tea tree stands. Also, shallow gum-topped box (E. polligaensis) are commonly regional groundwater levels occur in lowest landscape associated with sodic soils. positions, whereas localised perched watertables can occur in higher landscape locations. Pasture Where the presence of black tea tree, tea tree generally (Melaleuca sp.) and other local native In Queensland, the combination and relative vegetation species indicate the watertable is less than abundance of species provides the best indication of 6 m beneath the soil surface under native vegetation, salt levels, rather than the occurrence of any particular there is a high risk of water rising to the surface if the species. In general, poor pasture condition, including vegetation is cleared. patchy growth, reduced vigour and loss of salt- sensitive plants, can indicate salinity. A number of factors interact to determine species composition in a particular pasture. These factors include grazing regime, past management history (cultivation etc.), seed sources, soil conditions (such as compaction or low fertility) and seasonal
Salinity management handbook 49 influences. For instance, creeping saltbush (Atriplex found. Beyond this zone on relatively non-saline semibaccata) can be a good indicator of salinity as soils, black spear grass (Heteropogon contortus) it occurs on saline or disturbed soils (Christiansen communities commonly occur. 1993). However, this species is also generally absent The following table (Table 22) lists plant species from intensively grazed paddocks. that can be used to detect soil salting. Few of these Table 21. Dominant tree and shrub species indicating species can be considered true indicators of salinity salinity and sodicity in the lower Burdekin River–Elliot River because they also grow on non-saline soils. Some area, north Queensland (Thompson 1977). species are less common in non-saline areas due to competition with other, more vigorous species. Common Scientific name Indicative of soil If species known to have low salinity tolerance name conditions are found locally, their absence from areas of False Eremophila strongly sodic-saline, the landscape susceptible to salt outbreaks (see sandalwood mitchellii shallow topsoil, duplex Landform feature identification page 39) may also soils or saline grey clays indicate salinity. Such species include balloon Beefwood Grevillea moderately sodic soils cottonbush (Asclepias physocarpa), pitted bluegrass striata (Bothriochloa decipiens) and black speargrass Broad-leaved Melaleuca sp. waterlogging, at the (Heteropogon contortus). tea tree surface or in the soil profile; indicative on Figure 29. Marine couch (Sporobolus virginicus) found slopes of lateral ground- growing on a salt flat near Rockhamption, Queensland. water movement and shallow watertable Red Eucalyptus sedentary soils with bloodwood intermedia freely draining profiles; rock normally present in the profile Cocky apple Planchonia soils underlain by careya watertable confined in a washed sand stratum; also common in sedentary skeletal soil situations along subsurface seepage lines Pandanus Pandanus spp. deep sands, indicative of prior stream channel infills, and good quality water Boree Acacia pendula saline grey clays
The composition of species in salt-affected areas of south-east Queensland is not dramatically distinct from those found on non-saline soils (Christiansen 1993). Gradual changes in vegetation occur across the transition from non-saline through marginal to saline soil. In south-east Queensland, Rhodes grass, green couch and wild aster generally persist in all but the most severely salt-affected patches. In central Queensland, more defined transitions Vegetation patterns on remote are evident. Marine couch (Sporobolus virginicus), green couch, brown beetle grass, samphire, creeping sensing images saltbush, pigweed (Portulaca oleracea), coastal Vegetation density and growth vigour usually reflect pigface (Sesuvium portulacastrum) and soft roly-poly the available water regime. Potential recharge and (Salsola kali) occur on severely saline soils, while discharge areas can often be deduced from remote on the less saline margins purpletop Rhodes grass sensing images, preferably obtained before natural (Chloris inflata), woodland lovegrass (Eragrostis vegetation was initially cleared. sororia) and boobialla (Myoporum acuminatum) are
50 Salinity management handbook Table 22. Plant species which, when dominant and in Ground truthing must always be used to verify combination with other salinity indicators, indicate aerial photo interpretation. For instance, an area of that further salinity investigations are warranted (after increased vegetation density identified on an aerial Christiansen 1993). photo of the Charters Towers area had in fact been Common name Scientific name Indicates invaded by rubber vine. In this case, the increased soil vegetation density identified on the photograph was salinity not due to increased wetness and thus was not a level potential discharge area. Groundsel Baccharis halmifolia Buffel grass Cenchrus ciliaris Sources of information Barnyard millet Echinochloa crus-galli • Aerial photos and Landsat imagery are both Woodland lovegrass Eragrostis sororia suitable for looking at vegetation patterns. If Spring grass/cup Eriochloa procera possible, obtain images taken before natural grass vegetation was initially cleared as well as recent Caustic weed; mat Euphorbia dallachyana images. spurge • Vegetation patterns can also be readily observed Caustic weed; mat Euphorbia drummondii from vantage points in the catchment or by flights spurge over the area, if either of these are available. low to moderate Common fingerrush Fimbristylis dichotoma Gomphrena weed Gomphrena celesioides Interpretation Burr medic Medicago polymorpha Bare or patchy areas on remote sensing images Boobialla Myoporum acuminatum can indicate salted or scalded areas, particularly in Paspalum Paspalum dilatatum relation to particular landforms (see Landform feature Wild aster Aster subulatus identification page 39) and rainfall pattern over time Mueller’s saltbush Atriplex muelleri (see Moving average rainfall pattern page 56). Creeping saltbush Atriplex semibaccata Increased density of native vegetation in areas of Pioneer Rhodes Chloris gayana the landscape which are susceptible to salting is grass a reasonable indicator of increased wetness in the Purpletop Rhodes Chloris inflata landscape. Such areas would be at risk of developing grass salting if vegetation were cleared in the catchment Green couch Cynodon dactylon or other factors altered the hydrologic balance by increasing inputs or decreasing outputs. Sedges Cyperus sp. Brown beetle grass Diplachne fusca Linear patterns in vegetation can reveal geological features such as dykes or faults. It may be possible Ruby saltbush Enchylaena tomentosa to identify areas where specific indicator species Curly windmill grass Enteropogon acicularis dominate (see previous section). Changes in Epaltes Epaltes australis vegetation patterns around streams can indicate the Samphire Halosarcia and extent of alluvium and/or restrictions to catchment Sarcoconia
low to high outflows. African boxthorn Lycium ferrocisimum Black tea tree Melaleuca bracteata Hairy panic Panicum effusum Plant response to salinity and Pigweed Portulaca oleracea specific ions Soft roly-poly Salsola kali Most agriculturally important crops respond to total Prickly roly-poly Sclerolaena muricata salinity as an osmotic effect. Some woody horticultural Sea purslane Sesuvium species are also susceptible to concentrations of portulacastrum specific ions. When these concentrations reach toxic Sand spurry Spergularia rubra levels, effects are most noticeable in the leaves, Marine couch Sporobolus virginicus particularly in the leaf margins. Symptoms include necrotic spots, leaf bronzing and, in highly toxic Giant pigweed Trianthema portulacastrum cases, defoliation. (Details for a range of plants are given in Maas 1986.) The ions most often involved are sodium, chloride and boron.
Salinity management handbook 51 For a given species, an assessment of plant salt Using experimental data on salinity threshold and tolerance will depend on the purpose of growing the productivity decrease per unit of salinity concentration plant. Plant salt tolerance for crops is defined as the increase, it is possible to calculate the approximate ability of plants to survive and produce economic salinity level at which a particular yield may be yields under saline conditions. For ornamental achieved, using the equation: species, the ability to survive and maintain an Yr = 100 – B(ECse – A) ...... 21 aesthetic appearance may be more important where than yield.
Yr is relative yield EC is the nominated or measured value of Sources of information se EC • Advice on observable symptoms can be obtained se from the Department of Environment and Resource B is per cent productivity decrease per Management. dS/m increase above the threshold value • Information on other toxicity effects is provided in the Australian water quality guidelines for fresh A is salinity threshold value of ECse. and marine waters (ANZECC 1992, currently being An extensive listing of plant salt-tolerance data revised). (productivity decrease and threshold values) for a range of crop, pasture, fruit, vegetable and Additional information ornamental species is provided in the appendix Plant salt-tolerance data (page 124) with calculated EC There are essentially two types of plants which grow in values which may be expected to result in 90% and saline soils: salt-resistant and salt-tolerant plants. 75% yields. When using this data, it is important to Salt-resistant plants (glycophytes) maintain growth keep in mind the range of factors that influence plant in mildly saline soils by excluding salts at the roots salt-tolerance in the field. (Greenway & Munns 1980). In extremely saline soils, Most quantitative salt-tolerance data have been glycophytes are unable to both exclude salt and derived from controlled laboratory or greenhouse obtain sufficient water for maintenance and the plant experiments rather than under field conditions. tissues are sensitive to high concentrations of salts. In laboratory experiments, one factor (such as the Conversely, halophytes are those plants considered salinity) is varied while other factors (such as soil to be truly salt tolerant because growth continues type, nutrition, water) are usually kept constant. despite high internal concentrations of electrolytes. Obviously, many of these factors interact in the field; As a result, the upper limit of soil salinity that can in addition, the distribution of salinity in field soil be tolerated is much lower for glycophytes than for profiles will not be uniform as it is in most controlled halophytes. Some halophytes have adapted to ion experiments. uptake by secreting salts. Others cope with high For these reasons, salinity information which is internal ion concentrations by compartmentalising derived from controlled experiments is useful as salts or increasing the volume within which the salts a general guide, but can not be used to precisely are dissolved. Adverse effects of ion uptake in non- predict plant behaviour under the wide variety of adapted species include effects on metabolism, such field conditions. as a decrease in CO fixation. 2 A number of the factors affecting salt tolerance in the Halophytes which exclude salts at the roots use field are described in this section. mechanisms to avoid an internal water deficit. Non-adapted species in highly saline conditions are Salinity in the root zone unable to both exclude salts and obtain sufficient In glasshouse investigations, soil properties and water for maintenance, resulting in water stress. Most salinity are uniform throughout the root zone. In the agricultural species fall into this category. field, however, this uniformity is unlikely to occur. In reviewing the literature on relative salt tolerance for Two measures of root zone salinity in the field are a wide range of crops, Maas and Hoffman (1977) found commonly used to relate to plant response: average the normal response of plants to salinity appears to root zone salinity, and water uptake weighted root be that there is no yield decrement until a threshold zone salinity. (These two measures are described in level is reached, after which there is an approximately more detail in Root zone salinity page 34.) linear decrease in yield with increasing soil salinity. Maas and Hoffman grouped the response of relative yield to salinity into four salt-tolerance divisions, as shown in Figure 30.
52 Salinity management handbook Figure 30. Relative crop yield in relation to soil salinity may contain toxic amounts of ions (such as Na or Cl) (ECse) for plant salt-tolerance groupings of Maas and for weeks without exhibiting leaf necrosis until the Hoffman (1977). first bout of hot, dry weather.
100 Fertility Published data on the interaction between fertility and 80 salinity present contradictory conclusions. A range of experimental results were reviewed by Feigin (1985), who explained the contradictions in terms of the
60 different experimental procedures. Crops growing on infertile soils can actually show higher salt tolerance than crops of the same species 40 moderately sensitive grown on highly fertile soils. This is because salinity is
relative crop yield (%) m od not the main limitation to growth in this situation. era
te
sensitive ly unsuitable 20 to tolerant le ra Symptoms of salinity and specific ion n t effects on plants 0 The most common indications of salinity occur when 0 10 20 30 plants are stunted, grow slowly, or do not grow at all. soil salinity EC (dS/m) se In some cases, leaves may be a darker green and more succulent than usual. However, in most cases, Plant stage of growth the only indication will be reduced yield; dry matter production may be affected less than yield. Salt- While some species are more susceptible to salinity tolerant species such as pioneer Rhodes grass and at emergence than at later stages of growth, other green couch are often more productive in areas where species are in fact less susceptible at emergence. In watertables are close to the surface due to increased these species, a crop that appears to have germinated moisture availability. successfully under saline conditions may fail at a later stage of growth. Hence, the effects of salt both Some plants which are osmotically stressed by salt on germination and yield should be considered show no distinctive symptoms apart from the ones when choosing crops for marginal conditions. (This mentioned in the previous section and others related is discussed further in Crop species page 103. Table to normal water stress. Salt stress for most plants is 42 in that section lists some species for which Maas, an additional stress to water stress because the plant 1986, collated available information on salt-tolerance cannot develop sufficient energy to extract water. differences between germination and seedling Woody species tend to show more leaf damage than establishment phases.) herbaceous species. In woody species, leaf burn and even defoliation can indicate salinity. These Management practices symptoms tend to result more from the accumulation Some species can tolerate higher salinity of specific ions (such as sodium or chloride) than from concentration in the soil than in water applied to the total salt concentration. leaves. This is specifically relevant to crops under In addition, other elements not related to salinity, sprinkler irrigation. Management practices for using such as heavy metals, can cause a number of marginally saline waters include irrigating below the symptoms that are similar to salinity and specific leaves (to avoid depositing salts on the leaves) and ion effects. irrigating at night (to reduce salt on the leaves left by rapid evaporation during the day). (These practices Sodium are discussed in Marginal quality irrigation waters Excess sodium accumulates in the leaves, causing page 116.) leaf burn, necrotic patches and even defoliation. Climate (This is an effect of plants’ response to high levels of a specific ion rather than to salinity in general.) Poor According to some researchers (for example, Maas physical conditions in the soil (caused by sodicity) 1985), climate may influence plant response to salinity will limit plant growth (the major effect). Plants may more than any other factor. Plants are able to tolerate experience calcium and magnesium deficiencies salt better when the weather is cool and humid than because of reduced availability. when the weather is hot, dry or windy. In plants which are sensitive to high levels of specific ions, the leaves
Salinity management handbook 53 Excess sodium will degrade the physical properties of Figure 31. Leaf damage due to salinity on a young pine tree a soil. Sodic soils tend to disperse readily, affecting near Bundaberg, Queensland. air and water permeability, and form hard, dense clods when the soil dries. These physical effects prevent adequate root development and increase the difficulties of soil management. Limited root exploitation can result in nutritional deficiencies and greater likelihood of water stress. Sodicity problems occur less often on sandy soils and are compensated to some extent by swelling and shrinkage on cracking clay soils (discussed in more detail in Soil stability and sodicity page 23). Under continued irrigation with strongly sodic waters, the exchangeable cations on the clay mineral surfaces of the soil are gradually replaced by sodium until a new equilibrium is established. Deficiencies of calcium tend to arise because it precipitates out of solution as CaCO3 as the sodium exchanges onto the clay in alkaline soils. This occurs to a greater extent if the irrigation waters contain high levels of bicarbonate. Waters containing sodium bicarbonate (residual alkali) can develop soil pH up to 10.0, creating significant nutritional problems. (Refer to Irrigation water salinity and sodicity classification page 82 for further discussion of residual alkali.)
Chloride Plants affected by chloride toxicity exhibit similar foliar symptoms to sodium, such as leaf bronzing and necrotic spots in some species. Defoliation occurs in some woody species. Chloride behaves similarly to sodium. However, salinity impacts on citrus yield, long attributed to chloride levels in waters, have recently been found to be more closely related to EC. The evidence for specific yield reduction in citrus in relation to chloride or osmotic effects is a matter of debate. The current evidence strongly indicates that osmotic effects are the primary cause of yield reduction.
Boron Symptoms, such as yellowing margins, crumpling, blackening and distortion, appear first in the youngest leaves. The level at which a particular plant will find boron toxic depends on a variety of factors, particularly whether the boron originates in the soil or in the irrigation water. Boron toxicity is uncommon in Queensland, except in some areas of the south-west (Wreczycki 1968).
54 Salinity management handbook Chapter 8 — Climate and rainfall patterns
Average annual rainfall Interpretation characteristics The information in Table 23 (page 56) was derived by correlating salinity occurrences with rainfall/ In Queensland, watertable salting is mainly evaporation patterns at relevant locations. The data confined to lands receiving 600 to 1 500 mm of rain for correlating salinity risk with annual rainfall/ annually, with the most marked effects occurring evaporation patterns are based on water inputs from in lands receiving 700 to 1 100 mm of rainfall. (This rainfall alone. Clearly, additional inputs in the form is discussed in more detail in Seasonal rainfall/ of irrigation water (particularly from surface waters) evaporation patterns page 11.) will effectively increase the rainfall to a particular landscape.
Figure 32. Zones of salinity hazard in Queensland, based on annual rainfall/evaporation patterns.
Cairns
salinity hazard
high 700–1 100 mm/year moderate 600–700 and 1 100–1 500 To wnsville low <600 and >1 500
Mount Isa
Mackay
Rockhampton Emerald
Charleville
Brisbane
Salinity management handbook 55 This is illustrated graphically in Figure 32. Of course, years and the current year should be plotted against rainfall is only one factor determining the occurrence a year in question (that is, the average of years 1 to 5 of salinity. is plotted against year 5, the average of years 2 to 6 against year 6, and so on). This map indicates only broad areas in which salinity outbreaks are most or least likely to occur based on Figure 33 illustrates graphically the rainfall variability, current experience. as plotted from five-year moving averages, for a number of Queensland centres. Table 23. Correlation between average annual rainfall ranges and risk of watertable salting, based on input from Figure 33. Five-year moving average rainfall graphs for a rainfall alone (using average data available from the Bureau number of Queensland regional centres (data from Bureau of Meteorology). of Meteorology).
Average annual summer Indicative of salinity risk dominant rainfall (mm) < 600 low 600–700 moderate 700–1 100 high 1 100–1 500 moderate > 1 500 low
Moving average rainfall pattern By looking at the moving average rainfall pattern for a region, it is possible to compare the current rainfall pattern with historic patterns and to assess whether a current expression of salting would be likely to increase or decrease with a predicted rainfall pattern. (This is discussed in more detail in Long-term rainfall trends page 11.)
Sources of information • Australian Rainman, a computer package with climatic information from most Bureau of Meteorology stations throughout Australia, is available from the Department of Employment, Economic Development and Innovation. • Queensland’s Rainfall History (Wilcocks & Young year 1991) presents yearly, five-year and ten-year moving averages in graph format for 269 of Queensland’s weather recording stations from 1880 to 1988. Interpretation • Bureau of Meteorology data on rainfall are generally accessible. To consider how the current position in long-term rainfall trends ties in with salinity processes in the Calculation local area, annual rainfall information can be analysed in conjunction with evidence of salting (initial or A five-year moving average is commonly used and can recurrent) on remote sensing imagery (such as aerial be calculated and plotted manually or using graphical photos) and in other historical records of land use software. The manual method can be quite tedious. events such as clearing, irrigation, road or dam In brief, five-year moving averages are calculated by construction and so on. averaging the data for years 1 to 5, then for years 2 to The following points are intended as guides only to 6, then for years 3 to 7, and so on. Moving averages interpreting the effect of changes in long-term rainfall can be plotted against the first, last or middle year trends on current expressions of salinity or the effect of the span being averaged. Because the cumulative of activities which otherwise place a landscape at risk effect of rainfall in previous years is important when of salting (such as clearing). Further interpretations looking at salinity, the average of the previous four can be made readily from data at hand.
56 Salinity management handbook • If the current five-year moving average is less Practical example than the 100-year average annual rainfall and waterlogging or salinity are currently in evidence, Rainfall variability in the Clare area, south of then the severity of these problems is likely to Townsville, is very high (Figure 35). Salting was increase when annual rainfall exceeds the long- evident in some areas under native vegetation in term average (Figure 34). the early 1980s, due to higher rainfall periods and the strong influence of dykes within the landscape. • If the current five-year moving average is greater In 1986, areas which were salted in 1980 showed than the 100-year average annual rainfall and no evidence of salting and normal vegetation waterlogging or salinity are currently in evidence, was observed in previously bare drains. In 1992, then the severity of these problems may decrease following two cyclones and a very wet period, shallow when annual rainfall decreases (Figure 34). watertables and salted areas were more in evidence There is evidence that once a salinity problem than had been previously observed for a section of the develops in some regions (particularly those with lower right bank of the Burdekin River. Mediterranean climates), the problem is likely to Using aerial photographs from 1945, 1961, 1971 remain and possibly increase in size. In contrast, and 1979, salting was evident on some occasions, in summer-dominant rainfall areas, such as the depending on the rainfall pattern. This rough Burdekin area or the Lockyer Valley, the size of salinity analysis indicates that if the rainfall exceeds about outbreaks varies with rainfall. 1 100 mm for a few years, salting is likely to occur. Figure 34. Projection for the progression of salinity, Under irrigation, where more than 1 100 mm of water depending on whether waterlogging/salinity is in evidence input would be common, severe problems could be when the current five-year moving average is either above expected. or below the 100-year average annual rainfall.
5-year moving average 100-year average
watertable salinity becoming evident or increasing rainfall (mm)
watertable salinity not evident or decreasing
year
Figure 35. Rainfall variability for Clare, south of Townsville.
5-year moving annual rainfall average rainfall
5-year moving average average rainfall year 1980 = (rainfall 1976 + 1977 + 1978 + 1979 + 1980
year
Salinity management handbook 57 Chapter 9 — Soils
Figure 37. Gully erosion in a catchment near Mundubbera Soil properties resulting from land clearing and changed hydrology. A soil’s properties and behaviour largely determine how much water will move through the soil as deep drainage. Soil profile morphology can be a useful indicator of past salting or wetness. In Queensland, salting outbreaks commonly occur on clay soils. Duplex soils in Queensland may be associated with salting adjacent to the salted area. In Victoria and Western Australia, duplex soils figure prominently in salted areas, and contribute water to salted areas by lateral flow through the A horizon which is more permeable than the B horizon (Conacher 1975; Peck 1978). Soil characteristics such as mottling, colour and manganese and iron distribution in the profile indicate soil wetness. Wilson (1982) undertook a detailed study of the relationship between soil morphology and high watertables in the Ingham area. From the characteristics of soil mottles (amount, size, contrast and colour) and soil colour, the number of days a watertable fluctuates in a horizon and the number of days of waterlogging could be predicted. Powell (1985) discussed this subject further.
Figure 36. Development of mottles associated with a fluctuating shallow watertable in a soil used for sugarcane in South East Queensland. Soil morphology is particularly useful for identifying catena landforms (characterised by changes in soil properties down a slope, see Landform feature identification page 39) where soils are the product of weathering and salinisation under past water regimes. Examples are solodic and solonised solonetz soils in lower slope positions.
Sources of information • In addition to describing the soil directly, information on soils in particular areas can be obtained from the Department of Environment and Resource Management and CSIRO soil maps and reports.
Interpretation As rough rules of thumb, the following soil properties and features are generally relevant to salinity.
Soil pH Acid soils (pH < 6.5) tend to be soils with moderate to high deep drainage rates. Generally, the more acid the soil, the greater the deep drainage rate.
58 Salinity management handbook Neutral pH soils (6.5–7.5) are generally reasonably Figure 38. Columnar structure of the upper B horizon of a permeable. sodic texture contrast soil at Emerald, Queensland. The formation of these characteristics, including the sandy- Alkaline soils (pH 7.6–8.7) characteristically contain loam texture of the A horizon, can be attributed to the
CaCO3 in the profile. The equilibrium pH for CaCO3 is movement of dispersed clay in response to the hydrologic approximately 8.4 (depending on the partial pressure regime operating during soil formation. of CO2). Soils in this pH range have relatively low recharge rates unless derived from basaltic parent materials or other geological formations high in calcium. Strongly alkaline soils (pH > 8.7) indicate the presence of sodium carbonate or sodium bicarbonate since these two carbonates dissociate into a strong alkali. High pH is often characteristic of highly sodic soils since any available calcium is usually precipitated as
CaCO3. The remaining sodium replaces ions on the clay exchange sites.
Concretions Massive or numerous nodules of calcium carbonate
(CaCO3) at varying depths in the soil profile (but generally within the top 0.6 to 0.9 m) can indicate a historic seepage of waters with high calcium content.
CaCO3 precipitates out of solution on concentration or when the partial pressure of CO2 is reduced, such as at a watertable surface (see Processes controlling ionic composition page 74). CaCO3 nodules tend to occur in areas with high levels of calcium in the groundwater, such as in basalt regions. At the water–air interface in groundwaters rich in iron or manganese, oxidation results in the precipitation of iron oxides and/or manganese oxides as nodules or concretions, referred to as iron and manganese nodules. This occurs in acid soils.
Clay content and mineralogy Cracking clay soils have variable rates of deep drainage depending on the subsoil sodicity. More sodic soils have lower deep drainage rates. Low ESP soils have higher deep drainage rates, even with very high clay content, because the soils develop good structure. Soil depth is also a factor: deeper cracking clay soils have high plant-available water capacity and low redistribution of infiltrated water, resulting in lower deep drainage than shallower soils. Because high clay content montmorillonite soils are often low in sodium, they form well-structured, relatively permeable soils. Black earth soils with as much as 70% clay content can be quite permeable. Soils with kaolinite mineralogy are usually more permeable than soils with mixed clay mineralogy, such as kaolinite combined with montmorillonite or with illite.
Salinity management handbook 59 In summary, Table 24 lists properties of soils likely to 1. Add approximately 10 mL of distilled water, be found in possible discharge or recharge areas. rainwater or tank water (or other water, if none of these is available) to a centrifuge tube. Table 24. Soil properties typical of recharge areas or current or historic discharge areas. 2. Add small soil aggregates (to reduce breakdown time) until the contents of the tube increase by 5 mL Soil properties Likely indication to bring the volume to 15 mL. • mottling permanent, periodic 3. Add additional water to bring the total volume to 30 • gleying or historic discharge mL. area • manganiferous staining 4. Shake intermittently for 5 minutes and allow to settle for 5 minutes. • numerous CaCO3, silcrete, manganese or iron nodules 5. Dip an EC probe into the supernatant solution near soil surface (rather than the sediment) and take a reading. • fluffy soil surface • surface salts Note: A field test such as this provides a useful approximation of EC1:5, and correcting for bulk density will not improve the accuracy • bare wet areas with dead of the reading. Since field soils are often moist to wet, any bulk vegetation density effects will be confounded by moisture content. In surface • mottling shallow seasonal soils, bulk density is about 1 000 to 1 500 kg/m3, and in subsoils, up to 2 000 kg/m3. There are as many errors in reading the water • gleying or fluctuating watertable, possible level on the centrifuge tube as in correcting for bulk density. • indicators intensifying with discharge area depth, and soil becoming saturated with water Laboratory method • variable pH Soils are air dried (at 40°C) and ground (to less than • moderate to high salt content 2 mm particles) and then mixed into suspension in in subsoils a solution of one part soil to five parts deionised • permeable soils (e.g. sands, recharge area water at 25°C. After shaking for one hour and settling lithosols, krasnozems, non- for one hour, the EC, pH and Cl are measured. (For saline soils generally) a description of the Australian standard method for • shallow soils overlying measuring EC at saturation, refer to Rayment and weathered or fractured rocks Higginson 1992.) • weathered soils Interpretation and classification Soil salinity A range of soil salinity criteria is currently used in Queensland and worldwide. A number of these A range of direct and indirect laboratory and field criteria are specific to the areas in which they were methods are used to measure soil salinity. The more developed, so their application to Queensland common methods are listed in Table 25 (overleaf). conditions is limited. Most of these criteria were The first two tests in the table, EC of a 1:5 soil:water developed to provide rough practical guidelines for suspension and saturation extract, are described interpreting soil salinity data. Most soil processes in detail in Electrical conductivity as a measure of and values occur on a continuum, so criteria which salinity (page 30). Electromagnetic induction is suggest sharp class boundaries should be applied described in the section Landscape salinity mapping with some flexibility. The more commonly used criteria (page 43). are listed in Table 26. Techniques for measuring EC Shaw et al. (1987) developed a salinity classification 1:5 system based on plant salt tolerance, using a 10% Field method yield reduction value instead of the zero yield reduction of the Maas and Hoffman (1977) revision This method is appropriate for quick field tests. Field of the USSL (1954) scheme. Shaw et al. (1987) added test results will differ from laboratory results because an additional ‘very low’ salinity level for salt-sensitive soil drying, shaking and settling times are not horticultural tree crops (Table 27). EC1:5 ranges were standardised in the field. However, to simply identify derived for different clay contents which would be the order of magnitude of a salinity problem, these equivalent to the ECse soil salinity levels for each factors can be ignored. of the plant salt-tolerance groupings based on clay content and chloride concentration.
60 Salinity management handbook Table 25. Common methods for measuring salinity in soils.
Method Lab or field Advantages Disadvantages/limitations Use
1:5 soil water lab or field fast, routine too dilute, particularly in sandy soils fast field and lab survey suspension (up to 40 times more dilute than field water contents); sparingly soluble salts cause problems of over-estimation of salinity Saturation lab closer to field water tedious preparation quantitative evaluation extract content— 2 to 3 times of salinity, comparison more dilute across soils Electromagnetic field very fast non-linear depth integration; soil initial broad area survey induction properties and water content have some effect Time domain lab and field measures soil EC at expensive; technique not yet research, monitoring reflectometry field water content, sufficiently tested problems with signal also measures field strength in high CEC, soils; not as good water content for salt as for water content Soil solution field measures soil EC at tedious preparation; not for heavy clay research for evaluating extraction field water content soils degassed sample; high spatial leaching and deep variability; drainage, monitoring Soil solution lab accurate at field water very tedious; poor solution yield research displacement content Ceramic salinity field measure soil EC at very slow response; drift in calibration research, monitoring sensors field water content
Table 26. Soil salinity criteria in common use. The soil salinity rating is a description of the soil Assessment Comment salinity level which would correspond to the various scheme plant salt-tolerance groupings. USSL (1954) These are universally applied criteria using plant salt tolerance as the basis, The Maas and Hoffman (1977) plant salt tolerance and are well respected. Maas & Hoffman criteria are based on average root zone salinity for (1977) revised these criteria with small plants grown under high leaching fractions. The changes. The salinity categories apply if criteria in Table 27 can be used as the soil salinity ECse reaches the specified level anywhere level at which plants respond to salinity with the in the root zone. This makes the criteria specified groups of Maas and Hoffman, either as too conservative for Australian soils which have generally lower permeabilities average root zone salinity or as water uptake weighted than USA soils with consequent high salt salinity (discussed in further detail in Root zone accumulation at depth. salinity page 34). Northcote These criteria are based on the Cl These relationships and criteria have been & Skene content of a 1:5 soil:water suspension, incorporated into the SALFPREDICT component of the (1972) approximating an ECse of 4 dS/m of USSL (1954) above. Northcote & Skene SALF software package, which can be used to predict attempted to make the values more soil leaching fraction resulting from variations in relevant to Australian soils by considering applied water quantity and quality, root zone salinity, texture and incorporating a depth term. yield decline for nominated crops, deep drainage loss Values are only considered to a depth of 1 and deep drainage salinity. (This package is described m and maximum values within this depth are taken to be diagnostic. Chloride alone in Useful software packages page 141.) will provide an underestimate of salinity if gypsum or sodium carbonates are present. Bruce & These criteria do not relate particularly well Soil salt profiles Rayment to either of the above schemes and have Cl An examination of salt profile shapes to a depth (1982) levels lower than is normally encountered of, say, 1.5 m to 2 m is a fast and simple method of for the corresponding EC categories. These criteria are being revised. determining the hydrologic processes that may be occurring in a specific location in a catchment.
Salinity management handbook 61 Table 27. Soil salinity criteria ECse, and EC1:5 for four ranges of soil clay content (adapted from Shaw et al. 1987).
Plant salt- Corresponding Equivalent EC1:5 reading, based on clay content of soil (dS/m) tolerance ECse range2 Soil salinity rating grouping 1 (dS/m) 10–20% clay 20–40% clay 40–60% clay 60–80% clay
Sensitive crops < 0.95 < 0.07 < 0.09 < 0.12 < 0.15 very low Moderately 0.95–1.9 0.07–0.15 0.09–0.19 0.12–0.24 0.15–0.3 low sensitive crops Moderately 1.9–4.5 0.15–0.34 0.19–0.45 0.24–0.56 0.3–0.7 medium tolerant crops Tolerant crops 4.5–7.7 0.34–0.63 0.45–0.76 0.56–0.96 0.7–1.18 high Very tolerant 7.7–12.2 0.63–0.93 0.76–1.21 0.96–1.53 1.18–1.87 very high crops Generally too > 12.2 > 0.93 > 1.21 > 1.53 > 1.87 extreme saline for crops
1. These groupings are statistically derived divisions based on families of linear curves representing the salt-tolerance ratings of the majority of crops reported by Maas and Hoffman (1977). The terminology of Maas and Hoffman has been modified and an additional group of sensitive crops incorporated.
2. ECse given here is the boundary ECse at which 10% yield reduction occurs for these plant salt tolerance groups. The EC1:5 ranges have been determined from these ECse ranges using the equations provided in Converting from EC1:5 to ECse (page 30).
Based on long-term steady state conditions, the mass and the quantity of rainfall as well as the rooting of salt in a soil profile will be in equilibrium with the depth of the vegetation. Thus, some soils that also amount of salt entering the soil profile via rainfall and show reasonable recharge may have a normal soil salt weathering and the amount of salt leaving the soil profile shape, but at a relatively low concentration. profile via deep drainage (and a small amount in plant The discharge profile is indicative of evaporation uptake). of water brought to the soil surface from a shallow Since the salt content at any depth in the soil watertable by capillary rise. In the other profiles profile can be related to the relative rates of described above, the dominant source of water is evapotranspiration and soil hydraulic conductivity, the from the soil surface as rainfall. In this profile, the salt salt profile shape will reflect the hydrology of the soil. concentration at depth in the soil profile reflects the saline concentration of the shallow watertable. The Sources of information degree of salt concentration at the soil surface will depend on rainfall, leaching and surface salt flushing. • In addition to conducting soil salinity tests in the target area, soil survey reports are generally Figure 39. Typical salt profile shapes associated with available from the Department of Environment and recharge, discharge, normal and intermittent areas. Resource Management. EC1:5 (dS/m) 0 Interpretation Figure 39 illustrates typical salt profile shapes 0.3 associated with recharge, discharge, normal and intermittent recharge-discharge areas.
The recharge profile in Figure 39 is indicative of a 0.6 soil with high hydraulic conductivity and seasonal or annual flushing of the small amounts of salt that 0.9 accumulate as a result of evapotranspiration. soil depth (m) In the normal profile, the soil hydraulic conductivity intermittent discharge is low and plants utilise more of the water in the soil 1.2 normal profile, leaving salts behind. The depth in the root discharge zone below which salt concentration is essentially recharge constant represents the depth at which the roots are 1.5 not taking up water. Over long time periods, each small pulse of salt in the recharge water builds up the In a soil represented by the intermittent profile, general shape of the profile. The depth to the point the watertable may have fluctuated over a number of constant concentration varies with soil properties of years from being shallow enough to result in
62 Salinity management handbook salt concentration due to capillary rise, to deeper for example, a surface ESP of only 1 to 1.5 will depths where capillary rise is so low that it is contribute to soil crusting and reduced infiltration. essentially zero. In this case, the salt concentration This is not as severe a problem for Australian soils. is moved downwards by rainfall and upwards with An ESP of 15 or greater can be tolerated at subsoil the intermittent watertable rises, resulting in a fairly depths, particularly if the soil is a cracking clay soil. pronounced peak. This profile can also indicate The sodicity criteria given in Table 28 are not fixed bypass flow, where the soil is structured with values to be rigidly applied to all soils. Sands will macropores, allowing water to bypass the matrix into tolerate much higher ESP values than clay soils. This a better structured soil below the root zone. is illustrated in Figure 40, which shows the soil ECse required to maintain a soil structure for two soils of Soil sodicity different soil texture and various soil ESP levels. The figure is based on an annual rainfall of 1000 mm/year. The two most common measures of soil sodicity are: Figure 40. The threshold lines for two soils of different clay • exchangeable sodium percentage (ESP), being content and mineralogy for an annual rainfall of 1000 mm/y. the proportion of sodium adsorbed onto the clay The soils are unstable in the areas to the left of the lines mineral surfaces as a proportion of total cation and increasingly stable to the right of the lines. exchange capacity 30 • sodium adsorption ratio (SAR), being the relative clay 55–65% concentration of sodium to calcium and magnesium CCR 0.55–0.75 in the soil solution. 25 rainfall 1000 mm Measures of sodicity are explained in detail in Sodicity clay 25–35% in soils and waters (page 37). 20 CCR 0.35–0.55 rainfall 1000 mm
15
Sources of information SAR • Chemical analyses of soil samples and soil survey ⇐ unstable results and reports are the primary sources of 10 information.
5 stable ⇒ Interpretation and classification As for soil salinity criteria (discussed in Soil salinity 0 page 60), many of the criteria developed for 0.1 0.2 12 10 EC (dS/m) categorising soil sodicity were developed for average situations in specific areas. As a result, these criteria are not definitive. Northcote and Skene (1972) devised criteria that are useful for Australian soils (Table 28). Figure 41. Infiltration rates for soil surface of cores of Oster However, these criteria need to be considered in and Schroer (1979) and equilibrium lines for soil properties relation to soil properties, because the influence of at four rainfalls (after Shaw 1996). sodicity on soil behaviour varies with clay content and labels are infiltartion rate (mm/hr) for clay mineralogy (Shaw & Thorburn 1985a). In higher 30 water EC and soil ESP combinations clay content soils, lower ESP levels have a significant equilibrium curve for 2 000 mm rainfall effect on soil structure. equilibrium curve for 1 000 mm rainfall equilibrium curve for 500 mm rainfall Table 28. Criteria for classifying sodicity in soils (from equilibrium curve for 250 mm rainfall
Northcote & Skene 1972). 20
Criteria Description ESP < 6 non-sodic
ESP 6–14 sodic 10 ESP (0–76 mm depth) ESP > 15 strongly sodic
Soils of 30% to 50% clay with mixed mineralogy are most sensitive to ESP. In surface soils unprotected by 0 0.1 0.2 12 10 crop cover or mulch (and therefore subject to rainfall irrigation water EC (dS/m) energy), an ESP value of 3 is possibly a more accurate measure of ‘non-sodic’. For silty soils in Israel,
Salinity management handbook 63 The effect of the combination of EC and ESP on hydraulic conductivity is shown in Figure 41. Oster and Schroer (1979) evaluated the infiltration rate of various water qualities on cropped, 0.2 m diameter, 0.53 m long undisturbed soil cores. Infiltration rates were assessed after 19 months. The ESP of the 0–76 mm soil depth is plotted against the EC of the irrigation water in Figure 41. The threshold equilibrium lines at rainfalls of 250, 500, 1 000 and 2 000 mm/year from Shaw (1996) are also shown in the figure. The labels are the infiltration rate (mm/hr) for the irrigation water EC and soil ESP of the 0–76 mm depth of the soil columns. These data illustrate that there is no predefined threshold value of ESP above which soil permeability dramatically decreases. The equilibrium lines are similar to the hydraulic conductivity values, indicating the interdependence and effect of EC and ESP in maintaining the hydraulic conductivity of soils.
64 Salinity management handbook Chapter 10 — Waters
Field tests for waters The accuracy of the cheaper models is limited and these models are not calibrated readily. Cheaper Field tests are useful as a preliminary survey of the meters are often unable to read salinity levels less extent and distribution of salinity in a catchment or than 0.1 dS/m or greater than 20 dS/m. If dealing area. Water samples can be obtained from existing with an EC greater than 20 dS/m using a cheaper water access points (streams, wells, bores, irrigation EC meter, a measure can be obtained by diluting channels, dams), but the accuracy of the survey the sample, measuring the diluted sample, and will be limited by the spatial distribution of these multiplying the result by the dilution factor. points. Ideally, sampling points should be selected to Temperature has a significant effect on EC. If the represent a range of local geomorphological features EC meter in use does not have a temperature (including soils and aquifers) and land uses. compensated probe, readings should be adjusted to Table 29 (page 67) discusses a number of common the standard temperature of 25oC using the following field tests. For more detailed investigations or formula (Wells 1978): monitoring, specific advice is available from the Department of Environment and Resource ln K = ln K + β (t – t ) – β (t 2 – t 2) ...... 22 Management. t2 t1 1 2 1 2 2 1
Sources of information where
• As well as directly sampling surface waters and Kt1 is conductivity (EC reading) at field groundwaters, further information on waters in a temperature of sample number of areas is available from the Department Kt2 is conductivity (corrected EC reading) at of Environment and Resource Management, where standard temperature of 25°C an extensive database of this information is t1 is field temperature of sample being maintained. tested for conductivity • The Saltwatch program has resulted in the collation t is 25 (standard temperature) of a substantial database on the salinity of surface 2 β is 0.029 (coefficient for local natural waters and groundwaters. Further information is 1 waters) available from the Department of Environment and Resource Management. β2 is 0.00019 (coefficient for local natural waters). • Existing databases or reports of water or groundwater quality in an area may be listed with Queensland Spatial Information Council. Depth to the watertable The depth to the watertable can be measured using a Salinity and chemical composition plopper or other indicating device attached to a tape measure that can be lowered down a bore. A plopper Salinity in water samples can be determined on-site is simply a device that makes a plopping sound when using an EC meter, or samples can be forwarded it strikes the water surface. Old valves from internal to a laboratory for testing of salinity and chemical combustion engines (preferably with concave faces) composition. and brass plugs with concave faces make serviceable Samples for laboratory analysis should be forwarded ploppers. as quickly as possible. Delays and high temperatures A plopper can also be constructed from a 20–25 mm will result in salts precipitating out of solution, pipe with a cork or stopper blocking the inside of the changing the chemical composition of the water. pipe about 5 mm from the bottom end. Whistles and A wide range of EC meters is available, ranging from electrical devices can also be used. small pocket meters costing around $80, to small field It is important to record the reference point usedfor meters with temperature compensation costing about measurement; this is usually either ground level or $250, to multi-function extended range EC meters the top of the bore. For salinity investigations, it is costing upwards of $300. Mid-range meters with built- preferable to measure from the watertable to ground in temperature compensation are appropriate for most level. salinity investigations.
Salinity management handbook 65 The following steps should ensure an accurate Use of piezometers measure: Piezometers are very useful for assessing depth to • Measure the distance from the bottom of the the watertable, changes in water level with time and plopper to the end of the tape where it is attached rainfall events, elevation of the watertable above to the plopper. Add on this amount each time a a datum and hence the gradient of flow, estimated measurement is taken. flow capacity of the aquifer material, chemistry of • Lower the plopper into the bore until the plopper the water, and long-term monitoring of changes enters the groundwater. Pull up the tape slowly, associated with land use. jiggling the plopper up and down over a depth of about 50 mm until a plopping sound is heard every To assess flow regimes and the interrelationships time the plopper is lowered. Obtain an accurate of aquifers, hydraulic head (the pressure of the reading from the watertable to the top of the bore groundwater) needs to be assessed. This is usually casing or piezometer by jiggling the tape less and done using piezometers. By definition, a watertable less. Using this method, it is possible to accurately level will not exceed ground level, whereas the measure the depth to the watertable to within 5 hydraulic head associated with water in a confined mm. aquifer (such as the Great Artesian Basin) may be many metres above ground level. • To correct for the height of the bore or piezometer casing, hold the tape at the top of the inner edge of Piezometers measure pressure. The open well is a the casing, and then pull the tape down to ground specialised type of piezometer which indicates the level (Figure 42). Now read the measurement on the free water height of the watertable. Because water tape at the top inner edge of the bore casing or top tends to flow from areas of high potentiometric of piezometer. potential to areas of low potential, water levels in • Add the distance between the end of the plopper piezometers are useful for indicating the direction of and the beginning of the tape to the measure at water flow. the top of the bore casing. This will be an accurate The chemistry of dissolved salts in waters drawn measure of the depth to the watertable corrected from piezometers is useful for indicating the origins for the height of the bore casing. of the water and the chemical processes involved in determining the composition of the water. Trilinear Figure 42. Using a plopper to measure depth to the watertable (Saltwatch Instruction Book, DPI 1994). diagrams (described in Interpretation using trilinear diagrams page 76) can be used to graph chemical read at this point tape information for interpreting water sources and measure processes. Information on the installation of the AB piezometers can be used in conjunction with water level information to determine aquifer hydraulic conductivity, using, for example, the bail test of Bouwer and Rice (1976). Other information is needed to obtain a comprehensive interpretation of the water level and chemistry information obtained from piezometers. This information includes: ground • the bore log level tape measure • installation information, including depth, position and length of the slotted section of the tube and plopper depth to the sealing material water • rainfall records for the area (essential) • elevation of each piezometer, preferably above Australian Height Datum or otherwise some arbitrary height reference groundwater level • any information from deep bores in the surrounding catchment • observations of stream or spring flow, including water composition • observations on land clearing or other human activities, such as dams, roads etc.
66 Salinity management handbook Table 29. Common field tests for surface and groundwaters.
Field test Information provided Useful for Points to note
Surface water • salinity of surface water • can be used to construct • calibrate EC meter in a standard solution sampling • samples for chemical a preliminary map of • measure EC as soon as possible after obtaining composition analysis salinity in the catchment the water sample • can indicate salinity • if the sample is to be stored or transported processess and water before EC or laboratory testing, fill the sources container completely with the water sample to exclude air Surface water • data for calculating • useful in calculating flow rate volume of surface water catchment salt and water flow balances Groundwater • salinity of groundwater • identification of recharge • see notes for ‘Surface water sampling’ above sampling from existing bores or and discharge areas and • if a windmill is in operation, water can be wells groundwater collected from an outlet valve salinity maps • samples for chemical • can indicate water • if using a pump to collect water, run the pump composition analysis sources for some time (preferably 10 minutes) to clear stagnant water from the bore hole before taking a sample • if a pump is not available, a bailer (a plastic tube with a valve at the bottom that opens as the bailer falls and closes as the bailer is lifted) can be used to collect a sample. For accurate results, water should be bailed from the groundwater access point until new water flows in; as this is often impractical with a bailer, a compromise (less accurate than pumping) is to bail a few times and then let the bailer fall almost to the bottom of the bore or piezometer Depth to • current depth of • possible groundwater • it is important to use a consistent reference watertable watertable restrictions and likely point for measurements implications for surface • flow gradients and directions can be salting and plant growth; determined if piezometers are surveyed for gradient of water flow; elevation possible response of groundwater to rainfall
Installation Siting To obtain reliable information, piezometers must The design of piezometer installation will depend on be installed correctly (Figure 43). In defective the scale of the investigation. There are three broad installations, water response may be slow, surface types of installations: water could leak around the tube, or the sealing 1. Exploratory—a few piezometers are installed in around the tube may be inadequate, so that the selected areas to obtain a general picture of the pressure head will be under-estimated. Geritz (1985) area. provided specific details of piezometer installation 2. Overall trends—a broad network of piezometers and use. is installed across and up the catchment and To determine the vertical direction of water monitored in conjunction with existing bores and movement at a particular site, a series of two or more windmills (with the information from the existing piezometers (a ‘nest’) is sometimes installed. The nest installations being interpreted with caution). of piezometers may be installed in separate holes 3. Hydrologic modelling or detailed site analysis— or in the same hole with each individual piezometer a detailed network of piezometers is installed with terminating at a different depth, thus indicating piezometers set at several different depths and in the groundwater situation at each depth. Separate all landform features in the catchment. holes are preferred because the space around the piezometers can be sealed more effectively.
Salinity management handbook 67 Figure 43. Method for installing a piezometer Separate holes make it easier to seal the hole (after Geritz 1985). between the aquifers. It is important to seal immediately above the tapped aquifer, especially if it is below other aquifers. piezometer tube Differences in water heights in piezometer tubes can indicate the presence of perched watertables or soil backfill topsoil changes in the permeability of an unconfined aquifer.
Installing the piezometer PVC pipe is recommended for the piezometer tube prepared 10 cm hole 40–50 mm in diameter, class 9 or 12. This tubing is robust and should withstand rough treatment during upper confining material installation and operation. A section of the tube needs to be slotted to match the depth interval of the aquifer of interest. This is best done by hand, using bentonite plug a hacksaw frame fitted with two hacksaw blades spot-welded together to increase the thickness of the cut, or a power hacksaw can be used. Wider slots are
slotted tube with recommended because thin ones can clog with fine gravel fill to allow permeable water material and restrict flow. As an alternative to slots, groundwater access bearing layer holes can be drilled in the tube. Record the length to piezometer of the slotted section before installing the tube in the ground.
inpermeable basal If the drill hole remains dry or has little water in it confining layer after the drill is removed, installation should be straightforward.
Figure 44. Installation of piezometers using a small geotechnical drill rig in central Queensland. Drilling the hole Holes can be drilled using mechanical drilling rigs or alternative methods such as a hand auger or water jetting. A cutting head fitted with a replaceable tungsten carbide cutting tip is invaluable for drilling through occasional rocks as well as soil. Compressed air rock hammers may be required in hard rock. Isolated rocks (floaters) can give the impression that hard basement rock has been reached. With experience, drill operators develop a feel for rock hardness and this, together with local knowledge and observation of material emerging from the drill hole, is an acceptable guide for hole depth. The material brought up when holes are drilled provides valuable information about possible water pathways. It is important to keep a written log of observations while the holes are being drilled. Record any changes in the material (colour, texture, particle shape and size, concretions, wetness etc.), as well as the depth at which these changes occur. When drilling in an unknown area, there may be aquifers at various depths. An exploratory hole is necessary to identify the relevant aquifers, not only the first encountered. Each aquifer may be tapped by a separate piezometer and it will usually be simpler to put these down separate drill holes.
68 Salinity management handbook Figure 45. Measuring the groundwater depth and After setting the tube in the ground, pack gravel groundwater electrical conductivity simultaneously in a around the slotted section of the tube to prevent the piezometer. hole from collapsing at this point and to maintain good hydraulic conductivity. Recommended gravel size is 5–7 mm river gravel (passing a 5 mm sieve, retained on a 7 mm sieve). With 5–7 mm gravel, there is still sufficient pore space to permit water flow. Crushed metal (sometimes sold as gravel) has flat surfaces and may pack in the annulus of the tube. Coarser gravel can sometimes bridge around the annulus and block gravel falling to the bottom of the hole. The larger the gravel, the larger the pore space that will result. Coarse sand is more appropriate for sandy aquifer materials. Record the length of the gravel pack around the tube. Above this gravel pack, a watertight seal is essential to prevent leakage into the tube from other aquifers (usually higher) or from the surface. The recommended material for sealing above the gravel pack is granulated bentonite. Carefully pour the bentonite around the tube to a depth of about 100 mm, and preferably top this with a shallow layer of gravel. In theory, where the water level is above the slotted section, the bentonite will settle through any water in the hole and swell to form a seal. However, sometimes the bentonite swells before reaching the desired position and air gaps are formed. A more reliable seal can be obtained by pumping the piezometer to lower the water level below the top of the gravel layer before pouring in the bentonite. After the sealing layer is in place, backfill the rest of the hole to the surface and tamp the backfill into place. Build up a mound of soil around the tube at In coarse sandy material, the piezometer tube can the surface. Record details of sealing methods and be jetted down with high pressure water. In rigid depths. materials, water can be poured into the hole and the resulting slurry pumped out with a sludge pump. The piezometer above ground Jetting is another technique for clearing the hole— If the water level in the aquifer is not likely to rise injecting compressed air down the piezometer tube as above ground level, leave about 30–40 cm of the it is inserted so that material in the hole is lifted to the tube above ground level. This height is a compromise surface around the outside of the tube. This method is between being high enough for the site to be easily generally only effective if the slotted length of tube is identified and low enough to limit damage from cattle, relatively short. who often scratch themselves against the tube. The In unstable materials, the walls of the hole may tube can be further protected from cattle by driving collapse, making installation more difficult. three steel pickets (painted for visibility) into the Compressed air can sometimes be used to blow out ground around the piezometer and wiring the stakes slurried material but this can enhance the collapse together. For more permanent installations, a steel of the walls. Jetting water down an open-ended protective casing can be concreted around the tube. piezometer tube can also be used to clear the hole If the water in the aquifer is under considerable but, depending on the material, this could reduce the pressure with a hydraulic head above ground level, permeability of the material around the slots. the water pressure may break through the bentonite A mirror or a flat watch face is useful for inspecting seal. In this case, a longer tube will be needed, with holes by reflecting sunlight (when it is not overcast). appropriate support, and a cement grout should be used instead of bentonite.
Salinity management handbook 69 Place a slip-on PVC cap onto the top of the tube. A complete catchment water balance would require Ensure that there is a small hole in the cap or in the measurements of runoff, evapotranspiration side of the tube near the top to relieve air pressure from existing vegetation, and deep drainage in the tube. Mark a unique identifying label inside the (groundwater recharge) as well as groundwater cap or the tube. Record this identification information and surface water flow out of the catchment. Some with the other information on the installation of of these measurements, particularly estimation of the tube. evapotranspiration using water balance models, require a considerable amount of land use data and Operation are not sufficiently precise to accurately estimate deep drainage if this is less than 50 mm/yr. Estimating By reading the water level in piezometers frequently groundwater flow out of a catchment is also very during the first few months after installation, the difficult. Hence, the results of catchment water response of the piezometer and an indication of likely balance calculations need to be evaluated in the future response can be determined. Information on context of possible large errors. the response of the water level to rainfall events is particularly useful. From this information, patterns of recharge and delayed response can be detected, Groundwater balance model used to interpret readings on a catchment scale, and As discussed previously (in Rate of water movement related to soils, landforms and other features. (Refer in the landscape page 19), groundwater recharge to Depth to the watertable page 65). Piezometer is balanced by discharge in the form of subsurface loggers, which can be obtained fairly cheaply, can outflow, surface seepage, evaporation and be installed to obtain regular readings on changes in evapotranspiration. Expressing this relationship in water level response. the symbols used to express quantities of water (Salt page 17): To be able to assess flow directions, piezometer mass balance heights need to be surveyed to a common height datum. Because the elevation of the water surface Qd = Qg + Qs + Qe + Qt ...... 23 (pressure head) is being surveyed, standard survey methodology can be used. If the head is higher in This relationship can be expanded to incorporate one piezometer than others, this does not necessarily measurable parameters for investigating groundwater indicate that water is flowing. Head differences balance: usually indicate some restriction to flow (see Landform feature identification page 39). DdAr = Ks∆HAg+ S + EAb + ET Av ...... 24 Pump tests on piezometers can indicate flow rates in surrounding areas. There are a number of standard pump test procedures available, ranging from the where, using a time period such as a day, simple bail tests of Bouwer and Rice (1976) and later Deep drainage rate (D A ) (m3/d) (volumetric modifications, to more detailed pumping schedules d r rate at which water drains below the root zone, combined with taking measurements in surrounding approximating recharge to groundwater) is piezometers. Interpreting pump tests, particularly in regions with strong geologic flow controls, can be the deep drainage rate (Dd) (m/d) by the area over 2 difficult. Technical advice should be sought before which deep drainage (recharge) is occurring (Ar) (m ) carrying out these tests. Subsurface outflow from the discharge area K( s∆HAg) (m3/d) is Catchment groundwater the potential of the aquifer medium to conduct water (Ks) (m/d), by the hydraulic gradient (∆H) (m/m), by balance estimation the cross-sectional area of the vertical discharge face An estimate of catchment water balance can be of the aquifer at the lower catchment boundary (Ag) useful for initially assessing the magnitude of a (m2) salting problem, determining the most appropriate Surface seepage from the groundwater in the management options, and evaluating the amount of discharge area (S) (m3/d) is water to be managed in a salted catchment. the volumetric rate of water seeping from the Such an estimate will be rough because detailed groundwater in the discharge area, including base hydrologic measurements are generally not available. flow in drainage lines intersecting the discharge area (S) (m3/d)
70 Salinity management handbook Evaporation from bare areas in the discharge area Practical example (EA ) (m3/d) is b Data collected in the Darbalara catchment in the the evaporation rate from bare areas per day (E) Lockyer Valley were used to estimate the amount of (m/d), by the amount of bare area in the discharge excess water contributing to a salinity problem. (The 2 area (Ab) (m ) extent and progression of salting in this catchment is Evapotranspiration from vegetation in the discharge illustrated in Practical example following Human land 3 use and records page 88). Because the area of salting area (ET Av ) (m /d) is appeared to be in equilibrium with rainfall inputs, it the evapotranspiration rate from vegetation in the was assumed to have reached equilibrium. discharge area per day (ET) (m/d), by the amount of vegetated discharge area (Av) (m2). Results from catchment water balance calculations (provided in this section) were used to evaluate In some situations, aquifer parameters can be possible management strategies for the site. determined by conducting pump tests to determine transmissivity, which is the potential of a particular Groundwater inputs aquifer to transmit water per unit width. Hydraulic conductivity can be determined from transmissivity as Table 31 illustrates calculations of deep drainage follows: based on generalised information on soil properties available from a soil survey in the Lockyer Valley. T Deep drainage below the root zone can be estimated K = ...... 25 s h from soil salinity EC or from soil properties using SALFCALC (in this case, SALFCALC was used). The where catchment is 800 ha in area, and receives an average annual rainfall of 800 mm/yr. Three major soil types identified in the catchment are heavy clay in the
Ks is saturated hydraulic conductivity (m/d) lower catchment (approximately 50% of catchment), T is transmissivity per unit width of aquifer alluvial (approximately 25%), and upslope soils (m3/m/d) (approximately 25%). h is thickness (vertical) of aquifer (m). Reading from the calculations in Table 31, estimated Using transmissivity information to calculate deep drainage across the catchment is approximately 3 groundwater balance, the expression for the 306 m /d. subsurface outflow component is modified as follows: Groundwater outputs Values for groundwater output parameters and D A = Tw∆H + S + E A + ET A ...... 26 methods of measurement or approximation are shown d r b v in Table 32. From the data in Table 32, outputs (discharge): where = subsurface outflow + surface seepage + T is the transmissivity of the aquifer per evaporation from bare area + evapotranspiration 2 unit width (m /d) from vegetated area w is the width of the aquifer at the point of = K ∆HA + S + EA + ETA subsurface outflow from the discharge s g b v = 50 + 0.2 + 200 + 60 area (m) = 310.2 m3/d. ∆H is the hydraulic gradient in the system (m/m). Inputs versus outputs Because of conservation of mass, groundwater Sources of information and default inputs and groundwater outputs should equate once values equilibrium has been achieved. This calculation using Table 30 lists methods for estimating catchment approximate figures provides working values for groundwater balance parameters and some default groundwater input and output. The sensitivity of some values. Some parameters can be estimated from of the parameters can be evaluated by substituting aerial photos. A number of software packages provide different values and evaluating the results. Area other information (see the appendix Useful software terms are particularly sensitive variables. This serves packages page 141). to emphasise that this is only a rough estimate of catchment groundwater balance.
Salinity management handbook 71 Table 30. Guides for estimating or measuring catchment groundwater balance parameters, with some default values.
Symbol Parameter How to estimate or measure Units
Dd deep drainage rate Estimate an ‘average’ figure for deep drainage across the whole m/d catchment, giving proportional weight to each soil type depending on the percentage of the catchment that it covers. Can also be estimated from soil properties (using SALFPREDICT) or soil EC (using SALFCALC). Estimates range from approximately 50−100 mm/yr for shallow, well-structured soils or shallow soils in the rainfall range of 800−1 000 mm/yr, to approximately 1 mm/yr for sodic heavy clay soils. While deep drainage rates are often expressed on a yearly basis and deep drainage only occurs intermittently, for these water balance calculations mm/yr can be divided by 365 to give mm/day. 2 Ar area over which deep Measure on an aerial photo (use vegetation, soils etc. to identify m drainage (recharge) is zones) in conjunction with soil mapping occurring
Ks hydraulic conductivity (of Can be determined from piezometers set at appropriate sites; the aquifer) typical values can be used for types of underlying rock, obtainable from hydrology or groundwater reference texts. Values will be in the range 20−1 000 m/d. Alternatively, can be calculated from transmissivity values if these are available. ∆H hydraulic gradient (in the In the absence of detailed information on upslope water gradient, m/m vicinity of the discharge use soil surface gradient, estimating this from a contour map. area) 2 Ag cross-sectional area of Estimate from geology cross-sections, drill records, experimental m subsurface outflow (area of drilling. the vertical discharge face of the aquifer at the lower catchment boundary) S volumetric rate of Estimate from seepage flows and base flow in drainage lines m/d surface seepage from intersecting the discharge area. Surface seepage will vary over time, the groundwater in the so observed flow will provide an approximate value. Estimated discharge area and base as volume of seepage or flow rate by cross-sectional area of the flow in drainage lines seepage and/or intersecting the discharge area base flow. E evaporation rate from bare Value will vary with salinity of surface water and depth to m/d area in the discharge area watertable. A range of values may need to be tried. One option is 0.5 x Class A pan evaporation. The value 2 mm/d would be generally appropriate unless the watertable is at the soil surface. If the watertable is at the soil surface, evaporation rates will approximate class A pan evaporation rates and can be determined from Bureau of Meteorology climate maps and shire handbooks. 2 Ab amount of bare area in the Measure on the ground or from an aerial photo taken in a year with m discharge area near to average rainfall. ET evapotranspiration rate A value of around 1 200 mm/yr is probably reasonable. m/d from vegetation in the discharge area 2 Av amount of vegetated Measure on the ground or from an aerial photo taken in a year with m discharge area near to average rainfall.
These results indicate that evaporation from the 22 ML/yr by evapotranspiration, 18 ML/yr by bare area is the major mechanism balancing inputs subsurface outflow, and a comparatively negligible and outputs. This is why evaporative areas develop amount by surface outflow from the groundwater. following hydrologic imbalance in catchments. To bring the catchment into equilibrium and reclaim Converting the above information to ML/yr (m3/d the salt-affected area, more than 73 ML/yr of water x 365/1000), the above calculation indicates that will need to be disposed of by means other than recharge of approximately 112 ML/yr is balanced by evaporation. discharge of approximately 73 ML/yr by evaporation,
72 Salinity management handbook Table 31. Estimated deep drainage below the root zone for soils of the example—Lockyer Valley catchment. (Predicted leaching fraction is based on the assumption that present soil salt profiles reflect the new equilibrium under clearing, determined using SALFCALC.)
Predicted Deep drainage (Predicted leaching Area-weighted contribution to deep leaching fraction fraction x rainfall of 800 mm/yr) drainage (area x deep drainage as m/d) Soil type (determined using 2 3 SALFCALC) (mm/yr) (m/d) Area (m ) (m /d) Heavy clay 0.006 4.8 1.3 x 10–5 400 x 104 52 Alluvial 0.020 16 4.4 x 10–5 200 x 104 88 Upslope 0.038 30.4 8.3 x 10–5 200 x 104 166 Totals 800 x 104 306
Table 32. Estimated values for groundwater output parameters for the example—Lockyer Valley catchment.
Symbol Method of approximating value Calculation Value Units
Ks Estimated value from local knowledge 5.0 m/d ∆H Soil surface gradient from contour map used in the 1 m/100 m = 0.01 m/m absence of detailed hydraulic gradient measurements 2 Ag Apparent width at point of subsurface outflow from the 200 m x 5 m = 1 000 m catchment and depth determined by drilling S Approximate value based on observed flow 200 L/d ÷ 1 000 = 0.2 m3/d E Approximate value of 2 mm/day assumed 2 mm/d ÷ 1 000 = 0.002 m/d 4 2 5 2 Ab Bare area measured on an aerial photograph taken in a 10 ha x 10 m /ha = 10 m year having close to average rainfall (1982) ET Value of 1 200 mm/yr assumed 1 200 mm/yr ÷ 365 = 0.003 m/d 4 2 4 2 Av Vegetated area measured on an aerial photograph 2 ha x 10 m /ha = 2 x 10 m
Note: * Full conversions of units are shown. For example, 1 L/d = 0.001 m3/d; 1 mm/d = 0.001 m/d; 1 ha = 104 m2-.
Water chemistry and salt Electrical conductivity (EC at 25°C in dS/m) and pH are also measured in the laboratory. These tests, sources identification which can also be carried out in the field, have been Laboratory analyses of water composition provide described elsewhere. useful information for interpreting: Calculations from the water analysis are made to • likely sources of the water estimate total dissolved ions (TDI) and sodium • processes determining the composition (this is adsorption ratio (SAR). (This information can be particularly so on a catchment scale if more than a used to assess water quality for various purposes, as few samples are available) discussed in Water quality page 79.) • possible uses of the water. Theoretically, a balance between the total number of positively charged ions (cations) and the total number This information is also useful when deciding on of negatively charged ions (anions) is expected in appropriate management strategies. the analysis of any water sample. In practice, due to analytical errors and/or the existence of species Laboratory analyses which, although present, are not measured, some degree of charge imbalance is likely. Usually, the Routine laboratory analyses are: results should be within ±5%. Large discrepancies • soluble cations (Ca2+, Mg2+, Na+ and occasionally indicate an unusual water or an error in the analysis. K+) in meq/L, mg/L or mmole/L - - 2- 2- - • soluble anions (Cl , HCO3 , CO3 , SO4 and NO3 ) in meq/L, mg/L or mmole/L.
Salinity management handbook 73 Processes controlling ionic This dissociation into charged ions is the reason composition electrical conductivity measurements can be used to assess salt content. A natural water is an aqueous mixture of many As the concentration of the solution increases, the components, the concentrations of which are EC does not linearly increase with salt concentration. controlled by complex and interrelated chemical This is because neutral ion pairs can form without any processes as well as by the nature of the material the 0 0 charge, such as CaCO3 or CaSO4 , or with reduced water has been moving over or through. + charge, such as CaHCO3 . Gypsum is a classic Basic chemical processes and solubility example of this effect. For most salts in Table 33, the EC in dS/m is close to one-tenth of the concentration of salts in meq/L (for example, 10 meq/L NaCl ≈ 1 dS/m When water comes into contact with a mineral, NaCl). For a saturated gypsum solution, however, 30 dissolution begins and continues until equilibrium mmolec/L at saturation has an EC of 2.2 dS/m, due to concentrations are attained or until all the mineral ion pairing. Chemical analysis of a water assesses the is consumed. This may take thousands of years total concentration of an element such as calcium and if weathering is occurring, or days in the case of thus will give a higher salt reading. sparingly soluble salts. Thus, depending on the The low solubility of calcium compounds is the reason minerals encountered by natural waters, the salinity for the prevalence of lime (CaCO3) and gypsum in of natural waters can vary from only slightly more salty soils. Lime and gypsum are associated with salting than rainfall to even more salty than seawater. in alkaline soil areas. In some regions, thick layers of Table 33 lists the solubility of common salts. In lime are a good indicator of the presence of historic solution, these salts dissociate into ions—positively salting or wetness. Large gypsum crystals can be and negatively charged—and do not specifically exist present in seawater-affected tidal areas. as the theoretical compounds in the table. However, once the concentration of an ion in solution exceeds Effect of CO2 on solubility of carbonate the solubility of that ion, the compound precipitates compounds out of solution. For example, if a water containing The partial pressure of CO affects the solubility calcium, carbonate and bicarbonate is concentrated 2 of carbonate compounds. Rainfall dissolving CO by the plant or surface evaporation, calcium 2 from the atmosphere forms a weak acid (carbonic carbonate (CaCO ) would precipitate out of solution 3 acid HCO −) which is responsible for a considerable before calcium bicarbonate (Ca(HCO ) ) (see relative 2 3 2 amount of rock weathering. This is particularly evident positions of these salts in Table 33). in limestone areas where flowing water can dissolve CaCO . In soils and groundwater, the partial pressure Table 33. Solubility of common salts in millimolescharge per 3 litre of water (Doneen 1975). of CO2 is greater than the atmospheric CO2 partial pressure. In soils, this is due also to the effect of Salt Formula Solubility roots which increase the amount of CO2. When waters (mmolec/L) with higher partial pressures of CO2 are exposed Calcium carbonate CaCO 0.5 3 to the atmosphere, there is a release of CO2 (as in
Magnesium carbonate MgCO3 2.5 soft drinks) which can cause CaCO3 to precipitate. Evaporation or evapotranspiration from a watertable Calcium bicarbonate Ca(HCO3)2 3–12* fluctuating close to the soil surface can result in the Magnesium bicarbonate Mg(HCO3)2 15–20* precipitation of CaCO3. Calcium sulfate CaSO4.2H2O 30 Sodium sulfate Na2SO .10H O 683 4 2 Total salinity and common ion effect Sodium bicarbonate NaHCO 1 642 3 The data in Table 33 are based on pure salt solutions Magnesium sulfate MgSO .7H O 5 760 4 2 in water. For some salts, as the total salt concentration Sodium chloride NaCl 6 108 increases (also called ionic strength) the solubility
Magnesium chloride MgCl2.6H2O 14 955 of the sparingly soluble salts increases. This is particularly the case when salts are dissimilar. For Calcium chloride CaCl2.6H2O 25 470 example, NaCl will enhance the solubility of CaSO4. Note: * Solubility of carbonate minerals will be influenced by the On the other hand, if the ions are the same, for concentration of carbon dioxide (CO2) in the solution and soil air. example CaCl2 and CaSO4, or MgSO4 and CaSO4, there is a common ion effect where the amount of the less soluble salt in solution decreases.
74 Salinity management handbook This is readily illustrated by the data of Arslan and Figure 46. Effects of different salt solutions on gypsum Dutt (1993) plotted in Figure 46 which shows the solubility (plotted from data of Arslan and Dutt 1993). effects of different salt solutions on gypsum solubility. 50
MgCl2 Na2SO4 NaCl CaCl Sources of common ions 2 MgSO4 NaHCO3 Calcium 40 /L ) (c ) Calcium (Ca2+) occurs in waters which have been in contact with igneous and metamorphic rocks dissimilar ions containing the chain silicates (pyroxenes and 30 amphiboles) and feldspars. In sedimentary rocks, similar ions calcium commonly occurs as carbonates, for example limestone which consists mainly of calcite with admixtures of magnesium and other impurities. gypsum solubility (mmole 20 * Also, calcium carbonate can be present as a cement between particles in sandstone and other detrital rock. 10 bicarbonate The solubility of calcium in most natural waters is limited by processes involving carbon dioxide. The 0210 0304050 concentration of other ions (mmole /L) behaviour of calcium is generally governed by the (c) availability of the more soluble calcium-containing solids and by solution- and gas-phase equilibria Sodium bicarbonate is the least soluble of the processes, or by the availability of sulfate anions. common sodium salts. At room temperature, a pure solution of this salt would contain around 1 642 meq/L Magnesium of sodium. In natural waters, conditions favouring the
In igneous rocks, magnesium (Mg2+) is a constituent precipitation of NaHCO3 are unlikely to be attained. In of the ferromagnesian minerals including olivines, general, the solubility of sodium is rarely exceeded in pyroxenes, amphiboles and dark-coloured micas. Australian waters. There is, however, some evidence Metamorphic rocks have magnesium-rich species of the presence of solid NaHCO3 in some Burdekin such as chlorite, serpentine and montmorillonite. soils. The presence of solid NaCl (halite) is unlikely in In sedimentary rocks, forms of magnesium include normal agricultural situations, as a saturated solution carbonates (magnesite), hydroxides (brucite) and of NaCl can contain up to 6 108 mmolec/L of sodium calcium mixtures. and chloride (Table 33, page 74). Precipitation of NaCl can occur in agricultural situations only where soil Magnesium carbonate solubility is more complex than water, usually associated with shallow watertables, is that of calcium because of the many different forms concentrated at the soil surface by evaporation. of magnesium carbonates, hydroxycarbonates and hydroxides. Generally, these are more soluble than Sulfur calcium carbonates. Sulfur (S) is not a major constituent of the earth’s Sodium outer crust. However, sulfur is widely distributed, both in igneous and sedimentary rocks, as metal sulfides. It has been estimated that feldspars make up about Sulfur can also occur in certain igneous rock minerals 60% of igneous rock minerals in the earth’s outer of the felspathoid group. In sedimentary rocks, crust. Calcium and sodium feldspars are relatively sulfides or pyrites are commonly associated with more susceptible to weathering than potassium biogenic deposits such as coal. Evaporite sediments feldspars. Acid igneous rocks (such as granite) (such as gypsum) are another source of sedimentary contain higher proportions of sodium feldspars than sulfur. basic igneous rocks (such as basalt), which contain higher proportions of calcium and magnesium Sulfides can be oxidised by aerated waters to yield 2- feldspars. SO4 . Sulfate is chemically stable in aerated waters. CaSO4 is the least soluble common sulfate, with In sedimentary rocks, sodium may be present sodium and magnesium sulfates being many times in unaltered mineral grains, as impurities in the more soluble (Table 33). cementing material or as crystals of readily soluble sodium salts deposited with the sediments or retained following intrusions of sea water.
Salinity management handbook 75 Chloride Interpretation The chloride (Cl-) content of rock minerals is generally The direction in which points are plotted from the axes very low. Residual water in pores or included within is shown in Figure 47. The example point in Figure 47 crystals of igneous rocks may be a source of chloride. thus has an approximate analysis of 60% Ca2+, 20% 2+ + 2− − − More important sources are rainfall and sedimentary Mg , 20% Na , 10% SO4 , 25% HCO3 and 65% Cl . rocks where soluble chlorides may be present as Analyses dominated by Ca2+ will be plotted towards a result of inclusion of waters in the sedimentary the bottom left corner of the cation triangle. Similarly, process. Porous rocks formed in the sea or submerged analyses dominated by Mg2+ are plotted towards after their formation may also become impregnated the top of the triangle and Na+ the bottom right. For 2− with chloride salts. the anion triangle, analyses dominated by SO4 are plotted towards the bottom right corner, Cl− towards Chloride in natural waters is not altered by oxidation/ the top, and HCO − towards the bottom left corner. reduction reactions, does not form important solute 3 complexes with other ions, does not form salts of low On the square plot, the X axis (left to right) solubility (Table 33), and is not significantly adsorbed corresponds with the proportion of Ca2+ + Mg2+. High onto mineral surfaces. Ca2+ + Mg2+ analyses are plotted towards the left side, and high Na+ + K+ analyses (which must have low Ca2+ + Mg2+) towards the right side. Similarly, high Interpretation using trilinear diagrams − 2− Cl + SO4 analyses are plotted towards the top of There are a number of graphical and statistical − 2− − 2− the square, and high HCO3 + CO3 (low Cl + SO4 ) methods for assessing water analyses (some are towards the bottom of the square. reviewed by Freeze and Cherry, 1979). As discussed in Processes controlling ionic One useful method developed by Piper (1944) composition (page 74), when the concentration graphically illustrates the composition of a water of a mixed salt solution increases (for example in a form that can be linked to common geological by evaporation of water), salts of low solubility compositions and illustrates the processes of change precipitate and the composition of the soluble salts in composition that will occur. Using this approach, changes. An example of this is the concentration of the composition and concentration of salts can groundwaters by evaporation which commonly occurs be represented together. The method is useful for at saline seepages. When concentrated, soluble salt examining the similarity of waters in a region and for solutions tend to move toward the composition of evaluating concentration−precipitation reactions and seawater. the mixing of waters of different origins. Figure 47. Trilinear and quadrilinear diagrams, illustrating Method how points are plotted (after Shaw et al. 1987). The contribution of each of the major cations or anions is normalised by being expressed as a percentage of Test plot the total ions of the same type. The results are then CATIONS plotted spatially. For example, for the cations Na+, + 2+ 2+ - - 2- K , Ca and Mg and the anions Cl , HCO3 , CO3 and 2- SO4 , percentages are calculated as follows:
Na Na% = *100 ...... 27 Mg% Na + K% (Na + K + Ca + Mg2+) and
HCO3 HCO3% = *100 ...... 28 (HCO3 + CO3 + Cl + SO4) Ca%
Separate cation and anion plots and a combined cation/anion plot are shown in Figure 47. Traditionally, combined plots have been drawn on diamond-shaped quadrangular plots, but here the combined plot is presented on a standard rectangular plot for ease of plotting.
76 Salinity management handbook (black crosses). This is reflected in both the cation plot and the combined cation/anion plot. Some areas Test plot of overlap were expected because basalt overlies ANIONS the sandstones and basalt recharge will enter the sandstone. Also, the composition of very low salinity waters (EC < 0.05 dS/m) will reflect that of rainfall, which is similar to the composition of seawater. The composition of the waters in the alluvial aquifers C0 + HC0 % Cl% 3 3 of Tenthill Creek indicates a tight distribution of composition in a relatively narrow salinity range in the combined cation/anion plot. The cation plot indicates some relative enhancement of Mg2+ and Na2+ concentration and a loss of Ca+ with respect to basalt, as expected, due to the change in solubility SO4% with increasing concentration. The composition of the waters is dominantly of basalt origin.
Test plot The waters in Sandy Creek alluvial aquifers are CATIONS & ANIONS generally of higher salinity than Tenthill Creek Na + K% and show an increasing component of sodium as expected from Figure 48. The combined cation/anion plot suggests that, even with the increased relative concentration of sodium, the waters reflect the composition of a concentrated basalt-type water more Cl + SO % CO + HC0 % 4 3 3 than that of a water derived from a sandstone geology, since there is a strong absence of water composition in the top right corner of the combined cation/anion plot compared with the sandstone geology plot. If sandstones were making a significant contribution, there would be a higher sodium concentration. Ca + Mg% This is confirmed by the analyses of Hardie and Eugster (1970) who evaluated the evaporative Practical example concentration curve for closed evaporative basins of various geological water compositions. Figure 49 Figure 48 overleaf illustrates the practical use of shows their line for a basalt water and the respective trilinear diagrams in the Lockyer Valley to determine composition of waters for given salt concentrations in the most probable source of waters in the alluvial Sandy Creek in the Lockyer Valley. aquifers. In this case, chemical analyses of the water and interpretation using trilinear diagrams revealed Waters derived from basalt sources have that the common belief that the groundwater was approximately equal proportions of Ca2+, Mg2+ and coming from the uplands was likely to be incorrect. Na+ at low concentration (< 1 dS/m). As these waters Southern tributaries in the Lockyer Valley have concentrate to 2 to 4 dS/m, Ca2+ salts precipitate. been known to have variable salinity in the alluvial Further concentrations result in Mg2+ as well as Ca2+ groundwater. This alluvium is sourced mainly from precipitation. In basalt waters, this process leads to basalt materials. The surrounding uplands are an increase in Na+ dominance. sandstones. The commonly accepted theory was that Thus a simple analysis of waters using the trilinear clearing on the sandstone ridges resulted in increased diagram approach provides useful insights into seepage of sandstones waters into the alluvia. The chemical processes and geological sources of salts. In use of simple trilinear diagram plots indicated that this case, the implications for catchment management historic processes of salting in the basalt alluvium were that revegetation of the uplands, advisable if the were the source of the salts, and not the sandstones. sandstones had been the groundwater source, would Waters from the two major hard rock geologies in make essentially no impact on the alluvial salinity. the region, basalt and sandstone, are illustrated in the sandstone geology plot on the left side. Basalt waters (green crosses) show a greater Ca2+ and Mg2+ dominance than Na+ in contrast to the sandstone
Salinity management handbook 77 Figure 48. Use of trilinear diagrams to distinguish geological sources of water in relation to aquifer chemical composition and the effect of solution concentration on chemical composition (after Shaw et al. 1987).
Geology CATION PLOT Sandy Creek CATION PLOT Tenthill Creek CATION PLOT
Mg% Na + K% Mg% x Na + K% Mg% Na + K%
Ca% Ca% Ca%
Geology ANION PLOT Sandy Creek ANION PLOT Tenthill Creek ANION PLOT
CO3 + CO3 + CO3 + Cl% Cl% Cl% HCO3% HCO3% HCO3%
x
SO4% SO4% SO4% Geology Sandy Creek Tenthill Creek CATIONS & ANIONS CATIONS & ANIONS CATIONS & ANIONS Na + K% Na + K% Na + K%
xx x xx xxx xxx xx x x x x xxx x x x xx x % % xx % 3 3 x 3 x % % % 4
4 x x 4 x x x
+ HC O + HC O x + HC O 3 3 3 Cl + SO Cl + SO Cl + SO CO CO CO
Ca + Mg% Ca + Mg% Ca + Mg%
Geology EC dS/m
x = basalt x = < 1.75 x = 5.0 – 7.5 x = Marburg sandstone x = 1.75 – 5.0 x = > 7.5
Figure 49. Changes in cation composition with concentration for water derived from basalt in the Lockyer Valley compared with the data of Hardie and Eugster (1970) for a basalt water derived from closed evaporative basins in the USA (after Shaw et al. 1987).
line derived from closed basins in USA (Hardie & Eugster 1970) Mg% Na + K% line derived from basalt geology, Laidley, Tenthill, Wonga and Sandy Creeks in the Lockyer Valley
Ca%
78 Salinity management handbook Chapter 11 — Water quality
Water quality needs to be evaluated from the Interpretation and classification perspective of its intended use. ‘Suitability’ criteria for salt composition and concentration for domestic A number of factors affect an animal’s ability to use, for example, will be quite different from those for tolerate saline water (without undue harm to health), stock watering, irrigation and industrial uses. and these should be taken into consideration when applying any guidelines (ANZECC 1992; Gill 1986b; Water quality guidelines for a variety of uses in Winks 1963). The presence of high concentrations of Australia have been proposed by the Australia and certain compounds in drinking water may necessitate New Zealand Environment and Conservation Council adjustments to diet. (ANZECC 1992), based on earlier guidelines. The 1992 guidelines are currently under review. The ability of stock to tolerate saline waters depends on the levels of specific ions and salts as well as total salinity. Domestic use Some animal species can tolerate salinity better than Guidelines for water quality suitable for human others. In approximately decreasing order of salt domestic use have been developed by ANZECC (1992) tolerance are sheep, horses, cattle, pigs and poultry. and others (such as NHMRC). Older animals appear to be able to tolerate higher salinity levels than younger animals. Animals which Many aspects of water composition and quality are lactating or weak require better quality water. determine whether a water is suitable for human consumption. If stock are introduced gradually to marginally saline water, they can often adjust to the salinity levels. As an approximate guide for salinity only, total However, stock given saline water to which they salinity in drinking water should be less than 1 000 have not become accustomed can suffer ill effects mg/L (approximately EC 1.6 dS/m), based on taste or refuse to drink. Stock should be able to tolerate considerations. increasing salinity levels during dry periods because To determine whether a water is suitable for human they become accustomed to the changing levels over domestic use, submit water samples to local health time. However, stock are less tolerant of saline water authorities for a complete analysis. during hot, dry periods. It is during these times that stock need to consume more water, and that water supplies often become more saline due to evaporative Stock watering concentration. Highly saline waters can cause physiological Stock on green pastures or silage can tolerate higher disturbances in stock, such as gastrointestinal levels of salinity in drinking water because of the distress, wasting and sometimes death. Common (usually) non-saline water content of the pasture. conditions causing physiological stress, such as However, pastures grown on saline soils generally reproduction, lactation or rapid growth, place animals have higher salt levels and this also needs to be particularly at risk. In some situations, stock will considered when determining water requirements. refuse to drink saline water or will drink less than If stock are on prepared feed, the salt content of the usual. Stock may bypass saline water sources, or may feed should be assessed and possibly reduced to drink only enough to satisfy their salt needs. In other compensate for salt levels in water. Higher salinity situations, thirsty animals may drink excessively and levels can be tolerated if green feed is available near suffer ill effects. to the water supply, and stock do not have to travel The recommended guidelines presented in this some distance to obtain water. section are largely determined by field observation The total salinity levels presented in Tables 34 and not from rigorous experimentation (ANZECC 1992; and 35 are considered acceptable, provided the Gill 1986a). These guidelines consider the suitability concentration of specific ions or salts does not exceed of waters for stock from the perspective of salinity the limits in Tables 34 and 35, especially if salinity only. Other features of waters which would require concentration exceeds about 3.5 dS/m (ANZECC investigation include possible contaminants (heavy 1992). It is advisable to measure at least magnesium metals, pesticides or herbicides) and pathogenic concentration in addition to total salinity when organisms. (Guidelines for other water quality factors assessing waters for stock. are provided in ANZECC 1992 and Gill 1986b.)
Salinity management handbook 79 Table 34. Guidelines for upper limits of salinity concentration in waters for stock (after Hart 1974, in ANZECC 1992). See also Table 35.
Maximum concentration at Desirable maximum Maximum concentration that may which good condition might be concentration for healthy growth be safe for limited periods Stock expected
(dS/m) (TDS mg/L) (dS/m) (TDS mg/L) (dS/m) (TDS mg/L)
Sheep 10.0 6 000 22.0 13 000 * * Beef cattle 6.7 4 000 8.3 5 000 16.7 10 000 Dairy cattle 5.0 3 000 6.7 4 000 10.0 6 000 Horses 6.7 4 000 10.0 6 000 11.7 7 000 Pigs 3.3 2 000 5.0 3 000 6.7 4 000 Poultry 3.3 2 000 5.0 3 000 6.7 4 000
Note: *Depends on type of feed. Berkman (1989) suggests an upper limit of 14 000 TDS mg/L (23.3 dS/m).
Table 35. Alternative guidelines for upper limits of salinity concentration in waters for stock (Source: Gill 1986b).
Desirable maximum concentration Upper level for limited periods Stock (dS/m) (TDS mg/L) (dS/m) (TDS mg/L)
Sheep 15.0 10 000 21.0 14 000 Beef cattle 13.5 9 000 15.0 10 000 Dairy cattle 10.5 7 000 15.0 10 000 Horses 7.5 5 000 9.0 6 000 Pigs 7.5 5 000 10.5 7 000 Poultry 4.5 3 000 6.0 4 000
Some landholders may find that their stock animals Calcium thrive on water that is more saline than recommended. ANZECC (1992) recommends that if calcium is the Others may find their stock can only tolerate lower dominant ion, the concentration of total calcium in levels. This is to be expected, and will result from the stock water should not exceed 1 000 mg/L (Table 36, interaction of factors mentioned earlier. page 81). If the water contains high concentrations If most factors are favourable (climate, feed, stock of magnesium and sodium, the acceptable level of in good condition), there should be few problems calcium should be adjusted downwards. using stock water with salinity levels close to the recommended limits. Unfortunately, it is usually when Nitrate climatic conditions are unfavourable that marginal High levels of nitrate are not usually found in natural quality water supplies will be called on. It is advisable waters, except in water bodies containing decaying to manage the introduction of more saline water organic matter. Waters containing seepage from highly by mixing good and marginal quality waters or by fertile soils, areas fertilised with large quantities of conserving some good quality water and alternating nitrogen fertiliser, or effluent from intensive rural its supply with marginal quality water (Gill 1986b). industries may also have high nitrate concentrations Drinking troughs also need to be flushed out regularly (Gill 1986b). to remove salt concentrated by evaporation. Gill (1986b) held that animals can probably tolerate considerably greater levels of nitrate than the quantity Specific ion concentrations shown in Table 36. However, when nitrate is converted In addition to total salinity concentration, levels of to nitrite after ingestion, the nitrite combines with specific ions can be harmful to stock. haemoglobin, reducing the oxygen-carrying capacity of the blood. To reduce the risk, the water should be kept well aerated and free from contamination.
80 Salinity management handbook Table 36. Recommended upper limits for specific ions, salts Sodium bicarbonate or trace elements in waters for stock (adapted from ANZECC 1992, Gill 1986a, and Gill 1986b). Sodium bicarbonate in drinking water can cause sheep to bloat, particularly if the animals are under Maximum concentration (mg/L) stress and not accustomed to the water (Chippendale Specific ion (all stock unless otherwise specified) 1971, in Gill 1986a). The quantity shown for sodium or salt bicarbonate in Table 36 applies to stock that are not ANZECC 1992 Gill (1986b) accustomed to sodium bicarbonate in water; stock Major ions and nutrients may adjust to higher levels of sodium bicarbonate if Calcium 1 000 introduced to the water gradually. Nitrate sheep 60 pigs, 100 poultry Boron cattle 40 other stock 250 Boron may be present in groundwater, but horses 30 groundwater concentrations are usually less than the other stock 30 recommended maximum concentration. Excessive concentrations of boron can cause decreased appetite and loss of weight (Green & Weeth 1977, in ANZECC Nitrite 10 n/a 10 1992). Sulfate 1 000 1 000 Sodium n/a 1 000 Fluoride bicarbonate If waters with fluoride concentrations greater than the recommended level are used exclusively for young Trace elements stock for the first three years of life, the fluoride Boron 5.0 n/a has been found to weaken their teeth (Gill 1986b). Fluorides 2.0 2.0 High fluoride levels can cause bone lesions in older Magnesium Refer to Table 600 sheep 500 animals. High fluoride levels are normally found only in artesian and sub-artesian bores tapping the Great 37 for stock poultry 250 tolerances Artesian Basin (Gill 1986b). Such waters often contain of various young pigs 400 elevated sodium bicarbonate concentrations as well. salinity and other levels with stock If feed contains fluoride, the acceptable limit for magnesium fluoride in drinking water should be reduced to concentrations 1.0 mg/L (ANZECC 1992). less than 600 mg/L Magnesium High magnesium levels can cause scouring. Magnesium levels are a particular problem with many Queensland waters. In some cases, stock Nitrite have been reported as thriving on levels in excess Elevated levels of nitrite are not usually found in of those recommended by Gill (1986b, Table 36), natural waters, so they are not routinely tested for indicating either that stock may be able to adjust to when water samples are sent for analysis. If, for higher magnesium concentrations (Gill 1986b) or that some reason, the person supplying a water sample magnesium tolerance depends to a degree on total for testing suspects that nitrite may be a source of salinity (ANZECC 1992, Table 37). concern, this should be specified when samples are forwarded to the laboratory. Irrigation Sulfate The increasing demand placed on water supplies High sulfate levels can cause scouring and general throughout Australia will mean that irrigated loss of condition (ANZECC 1992, Gill 1986b). In agriculture faces the challenge of using less and/ Queensland, sulfate levels alone are rarely a problem or poorer quality water to maintain production. An as high sulfate concentrations usually occur only in increased reliance on groundwaters and reuse of waters with high general salinity. surface waters means that water quality will be ‘poorer’ than surface water or rainwater. The salinity and sodicity levels of these waters will be higher than surface water supplies and irrigation management will need to be modified to enable sustainable use of these poorer quality waters.
Salinity management handbook 81 Irrigation water quality criteria depend on soil in increased salinity levels as more salt is added properties, climate (rainfall in particular), plant with each application of irrigation water. The extent species and management practices. Since these of this problem is difficult to assess and can be factors interact to define acceptable quality in a given partly controlled by choice of salt-tolerant crops and situation, water composition alone provides only a water management strategies. Where supplementary rough guide under average conditions. irrigation (irrigation at levels less than annual rainfall) is the norm, salinity is of less concern than sodicity A number of irrigation water assessment guidelines because salt levels can be reduced dramatically by have been developed over the years. Schemes which wet season rainfall. have been in common use in Australia are listed in Table 38, along with their rationales. Shaw et al. Inherent in the philosophy of many of the water (1987) provide a more detailed discussion of some quality guidelines for irrigation is the control of soil significant problems with the extrapolation of these salinity by leaching with increasing levels of water guidelines to Queensland conditions. The main application. This is satisfactory for permeable soils, limitations of these schemes are: but for slowly permeable soils (1–10 mm/d for a • local region derivation for soil and climatic range of Queensland soils), leaching is dominantly conditions not readily transferable to Queensland controlled by soil properties rather than irrigation conditions water management. For clay soils, leaching is strongly influenced by the salinity and sodicity of the irrigation • conditions of use not defined water. Thus, threshold values are needed which • too conservative define the boundary between stable permeability and • most of the sodicity evaluations incorrect decreasing permeability for combinations of irrigation • salinity classes cannot be readily related to plant water salinity (EC) and SAR. salt response. Decreasing permeability is generally the result of Table 37. Suitability of water as livestock drinking water increased soil surface dispersion due to insufficient with magnesium < 600 mg/L and various concentrations of salt content within the surface layers to flocculate salinity (EC dS/m). the soil. This problem is obvious with rainfall events after irrigation with sodic waters. In rainfall periods, Salinity criteria with the total salt content in the surface soil solution is magnesium < 600 mg/L lowered by leaching. The ESP will not be reduced as Recommendations EC much because in a given volume of soil the number TDS (mg/L) (dS/m) of exchangeable ions (that is, ions held on exchange < 7.8 < 5 000 sites on soil particles) is generally 50 to 500 times 7.8–15.6 5 000–10 000 Generally unsuitable greater than the number of ions in the soil solution. for lambs, calves and Consequently, the number of calcium and magnesium weaners. Caution needed ions available in the soil solution is much lower than with lactating stock if the number needed to replace exchangeable sodium. unaccustomed. Suitable for dry, mature sheep and If EC becomes too low to counteract the effects of cattle. exchangeable sodium, clay swelling and dispersion > 15.6 > 10 000 Suitable for dry, mature occurs, resulting in reduced infiltration rates and soil sheep. Caution needed with permeability. cattle if unaccustomed. A relationship between ECse and ESP was determined Note: Magnesium levels > 600 mg/L generally unsuitable for all from an examination of the properties of subsoils stock. (Flinn 1984 in ANZECC 1992). of non-irrigated soils across a wide range of rainfall environments in Queensland (Shaw & Thorburn 1985a, Shaw 1996). This relationship reflects the Irrigation water salinity and sodicity natural equilibrium between EC and ESP that develops classification under a given rainfall, and can be used to establish guidelines for the permissible SAR of an irrigation Irrigation salinity can develop from watertable salting, water (Table 39). These guidelines were developed for or from the use of poor quality irrigation water. a permissible SAR which should maintain surface soil Salting from the use of poor quality irrigation water stability under high leaching situations associated occurs in irrigated soils where there is insufficient with heavy rainfall, due to the reasons highlighted leaching to remove salts from the root zone, resulting previously in this section.
82 Salinity management handbook Table 38. Irrigation water quality guidelines in use in Australia.
Assessment scheme Comment
USSL (1954), • Guidelines on salinity and SAR based on plant response. Hart (1974), • SAR criteria based on amount of sodium added to the soil and not in agreement with current views VIRASC (1980), of the influence of sodium on stability of the soil. ANZECC (1992) • Salinity criteria are conservative and don’t account for rainfall. Rhoades (1983) • Predicts salinity, sodicity and concentration of toxic solutes in the soil water within a simulated crop root zone under irrigation with a specified water composition and specified leaching fraction. • Evaluates effects of predicted salinity on crop yield and the effects of predicted surface soil sodicity on soil permeability. • Computer version WATSUIT uses an equilibrium chemistry model with options to consider the water composition amended with gypsum or sulfuric acid. The resultant predictions are then compared with the crop salt-tolerance data of Maas and Hoffman (1977) to determine crop suitability. • Appropriate where soil leaching fraction is known and can be varied with irrigation water management. • No account is taken of changes in soil leaching with increased electrolyte or sodicity under irrigation, which is particularly important for clay soils. • Model copes well with waters containing gypsum. Cass & Sumner (1982) • Based on earlier work of Cass (1980) incorporating soil and climatic factors in a water quality assessment method based on the model of Bernstein (1967) for slowly permeable soils. • Incorporates an empirical ‘sodium stability model’ to evaluate soil hydraulic conductivity reduction and aggregate stability with varying electrolyte and sodicity levels. • Crop yield is determined from the predicted soil solution composition related to the data of Maas and Hoffman (1977) through a yield index. • Difficulties with the model for Queensland are the requirement for a measured or estimated soil drainage flux, particularly for clay soils; model doesn’t allow for increases in soil drainage flux with increased electrolyte concentration; the use of laboratory measured hydraulic conductivity on disturbed samples is not related to field processes in soils with macropores (Bouma 1983); and the significance of unsaturated flow in leaching in slowly permeable soils is probably higher than the low saturated hydraulic conductivity values would suggest. Ayers & Westcot (1985) • First published in 1976 with a revised version published in 1985. • Method for identifying potential infiltration problems due to SAR as modified by EC has been adapted from Rhoades (1977) and Oster and Schroer (1979). • Recommends use of an adjusted SAR concept as developed by Suarez (1981) which offers better insight into the change in calcium concentration in the soil water due to addition by dissolution of calcium from soil carbonates and silicates, or loss of calcium from soil water by precipitation as carbonates. • Water quality evaluated by salinity effect on water infiltration rate, toxicity and a group of miscellaneous problems (such as high nitrogen and high iron concentrations). • The need to incorporate rainfall into the guidelines is a limitation for application in Queensland.
Residual alkali Residual alkali (RA) is another measurement often with a consequent increase in the ESP of the soil. considered when determining the likely impact of The adjusted RNa approach of Suarez (1981) as water quality on soil properties. Residual alkali recommended by Ayers and Westcot (1985) will correct represents the excess of sodium bicarbonate and for the effect of residual alkali on ESP. Residual alkali carbonate ions over calcium and magnesium ions on its own is not a useful indicator of sodicity hazard in the water. These salts combine with calcium and as waters may have high SAR and little or no RA, for magnesium in the soil solution, removing them example when sodium chloride is the dominant salt. by precipitation. This leaves an excess of Na+ ions
Salinity management handbook 83 Table 39. Guide to permissible SAR of irrigation water to maintain a stable soil surface following heavy rainfall periods.
Permissible irrigation water SAR* Clay mineralogy expressed as CCR (molec,kg) Clay content Soil texture 0.75–0.95 > 0.95 very (%) < 0.35 0.35–0.55 0.55–0.75 strongly strongly non-cracking** non-cracking cracking** cracking cracking < 15 sand, sandy > 20 > 20 > 20 > 20 > 20 loam 15–24 loam, silty loam 20 11 10 10 8 25–34 clay loam 13 11 8 5 6 35–44 light clay 11 8 5 5 5 45–54 medium clay 10 5 5 5 5 55–64 medium–heavy 5 5 5 4 4 clay 65–74 heavy clay – 4 4 4 4 75–85 heavy clay – – 4 5 5
* Values calculated assuming surface soil EC equal to undisturbed soil in Lockyer Valley, modified from Shaw and Thorburn (1985a) at 2000 mm rainfall. ** Cracking or non-cracking applies only if clay content is greater than about 35%. Plant response to saline irrigation One limitation of the general guidelines is the use water of 15% leaching fraction to estimate plant response. Table 5 (page 23) highlights the range of leaching When assessing water quality for irrigation, the fraction values possible for various soils. recommended approach is to assess water quality parameters and soil properties. With this information, Soil sodicity response to irrigation leaching fraction can be determined, from which soil root zone salinity and plant response can be Sodium in waters and the soil solution is usually determined (refer to Converting leaching fraction to expressed as SAR because of its close relationship root zone salinity page 36). Other factors such as with the ESP of the soil. The proportions of Ca2+, Mg2+ climate, crop type and irrigation management are also and Na+ on the soil exchange are not identical to the important when making recommendations on water proportions in the soil solution because the divalent suitability. cations are preferentially adsorbed onto the clay exchange surfaces. ESP can be calculated from SAR The following criteria (Table 40) are proposed as using the relationship of USSL (1954): general, broad guidelines for average conditions based on the plant salt-tolerance groupings of Maas 100(–0.0126 + 0.01475SAR) and Hoffman (1977) and using an average of 15% ESP = ...... 29 1 + (–0.0126 + 0.01475SAR) leaching fraction without considering rainfall.
Table 40. Irrigation water quality criteria for salinity based This equation has been found to provide practical on 90% yield of the plant groupings of Maas and Hoffman predictions in many situations including Australian (1977), assuming 15% leaching fraction. (Details of the soils (Skene 1965). derivation of the criteria are provided in Shaw et al. 1987) The reverse equation for obtaining SAR from ESP Irrigation water quality based on the regression of the original USSL (1954) Water (assume LF = 0.15) Plant salt-tolerance data is as follows: salinity EC Chloride grouping rating (dS/m) (mg/L) SAR = 0.6906ESP1.128 ...... 30 < 0.65 < 220 very low sensitive crops (R2 = 0.888) 0.65–1.3 220–440 low moderately sensitive crops 1.3–2.9 440–800 medium moderately tolerant This equation is valid for ESP values between 0 crops and 50. Details are given in Useful conversions and 2.9–5.2 800–1500 high tolerant crops relationships (page 158). 5.2–8.1 1500–2500 very high very tolerant crops > 8.1 > 2 500 extreme generally too saline
84 Salinity management handbook Predicting changes in SAR 1 0.5 SARd = SARiw ...... 32 The SAR of a water provides an indication of the effect ( LF ) an irrigation water is likely to have on a soil. A number of factors influence the relationship between ESP and where
SAR. In particular, the proportion of bicarbonate and SARd is SAR of the deep drainage water at the calcium ions can result in the precipitation of CaCO3, bottom of the root zone removing Ca from the system. Also, with depth in the SARiw is SAR of the irrigation water. root zone, the soil solution is concentrated by root water extraction, resulting in precipitation of the less Predicting changes in ESP soluble salts. However, the partial pressure of CO2 is higher in the root zone due to root activity, with the While changes in the soil salt content under irrigation result that carbonate salts remain in solution. are reasonably rapid (occurring in a matter of Additionally, the amount of deep drainage (or months) for the surface 0.1 m, changes in cation leaching) has an important effect in changing the exchange composition in the subsoil may take many concentration of salts in the root zone. Prediction years to come to equilibrium. The rate of change of leaching from soil properties as outlined in is proportional to the quantity of salts added. For Relationship between salinity, sodicity and soil example, an application of 530 mm/yr of an irrigation properties (following) provides the theoretical water with an EC of approximately 5 dS/m to a clay background to allow incorporation of salinity-sodicity soil with a CEC of 50 meq/100 g would contribute an relationships into prediction of the impact of sodium additional 6% of cations to the exchange complex in in irrigation waters. Relationships developed to the top 0.6 m of soil each year. predict changes in SAR under irrigation (Suarez, 1981; Miyamoto, 1980) require an estimate of leaching Relationship between salinity, sodicity fraction, hence the importance of integrating salinity and soil properties and sodicity responses into a unified soil property model of salt leaching and water movement. The behaviour of field soils is an integration of salinity and ESP as modified by clay content, clay mineralogy Suarez (1981) developed a model for the SAR of the and rainfall (see Figure 50). During soil genesis, the drainage water at the bottom of the root zone. This extent of clay migration to void spaces in the matrix point was chosen because it would theoretically determines the ‘resistance’ of the soil matrix to water reflect the highest SAR reached in the soil profile. movement. The mineralogy of the clay determines the swelling capacity and the ability of the subsoil to Naiw LF restructure and create porosity. SAR = ...... 31 d Mg 0.5 The equilibrium between salt balance, ESP and soil iw + Ca ( LF d ) properties explains the differences between field and where laboratory responses across a wide range of soils with varying clay contents and clay mineralogies. SARd is SAR of drainage water at the bottom of the root zone Figure 50 summarises the conceptual framework LF is leaching fraction and the main relationships. The relationships are illustrative only, to show the pattern of response. Na , iw Figure 50(a) shows that soils with low ESP have low Mgiw are Na and Mg concentrations in the ECse due to good leaching, even under relatively low irrigation water (in mmole/L) rainfall. Figures 50(b) and 50(c) show the influence
Cad is Ca concentration in the drainage water of particle packing and clay mineralogy on salt accumulation which is strongly influenced by ESP. From a combination of these two figures, soils with Ca is predicted from the ionic strength, HCO /Ca d 3 high clay content which are also dominated by ratio, and partial pressure of CO2. Cad values can be montmorillonite mineralogy show lower ECse than lower calculated from data given by Suarez (1981). Work clay content soils with mixed mineralogy, particularly is currently being undertaken within the Department at ESP values greater than 5. Figure 50(d) shows the of Natural Resources to incorporate this type of effect of rainfall on the equilibrium relationships prediction into the SALFPREDICT model to further between ESP and ECse. The range in equilibrium value improve its ability to predict leaching fraction and root for a given ESP is related to the water available to zone salinity under varying water qualities. move through the restriction of the soil matrix. An alternative approximate prediction of the effect of Deep drainage is inversely related to EC , thus soils sodic irrigation water on the SAR in the root zone is se with low ECse have high deep drainage for a given provided by Miyamoto (1980): water input. Salinity management handbook 85 Figure 50. The conceptual framework for the soil salt balance in relation to soil properties, showing the contribution of rainfall and the soil properties of clay content, mineralogy (as CCR) and ESP to subsoil ECse. ECse is the inverse of drainage below the root zone.
30 40 ESP 50 ESP 40 ESP 25 ESP 25 ESP 5 ESP 15 ESP 1 30 ESP 5 ESP 1 20
20 (dS/m ) (dS/m ) se se EC EC
10
10
0 0 1 000 2 000 3 000 0420 0 60 80 100 annual rainfall (mm) clay content (%)
(a) Relationship of ECse with rainfall and ESP. (b) Relationship of ECse with clay content and ESP.
15 60 ESP 40 A 250 mm rainfall ESP 25 B 500 mm rainfall A ESP 15 50 C 1 000 mm rainfall ESP 5 D 1 500 mm rainfall ESP 1 E 2 000 mm rainfall B 10 40
C 30 (dS/m ) se ESP (%) D EC
5 20 E
10
0 0 00.5 1 10–1 100 101 102
CCR (molec/kg) ECse(dS/m)
(c) Relationship of ECse with CCR and ESP. (d) Equilibrium lines for ECse and ESP, and the effect of rainfall.
86 Salinity management handbook Other factors in irrigation water quality In addition to salinity and sodicity, a number of other issues need to be considered when looking at water quality for irrigation, such as plant response to high levels of specific ions or excessive nutrients, and the effect of salt and mineral deposits on plants and on equipment.
Specific ion toxicity Toxicity problems occur when certain ions in the soil or water are accumulated within the plant at concentrations high enough to cause crop damage or reduced yields. The degree of damage will depend on the amount of ion uptake and crop sensitivity. The ions of primary concern are chloride, sodium and boron. (Specific ion toxicity is discussed in some detail in Symptoms of salinity and specific ion effects on plants page 53.) Toxicity can also occur as a result of direct absorption of the toxic ions through leaves wet by overhead sprinklers. Sodium and chloride are the ions most likely to be absorbed through leaves, and toxicity to one or both can be a problem with certain sensitive crops such as citrus.
Excessive nutrients High nitrogen concentrations in an irrigation water can cause excessive vegetative growth, lodging and delayed crop maturity. Water high in bicarbonate or iron content or containing gypsum and distributed by overhead sprinklers can leave deposits on fruit or leaves.
Equipment problems Salinity concentrations and precipitates can corrode irrigation equipment and cause scaling. Suspended organic and inorganic sediments can clog gates, sprinkler heads and drippers. More commonly, sediments accumulate in channels and ditches, requiring the costly maintenance of waterways.
Salinity management handbook 87 Chapter 12 — Human activities
Human land use and records Interpretation Changes in land use over the period since When analysing information on land use, consider development, when associated with the rainfall whether the following effects, commonly associated pattern over time (see Moving average rainfall pattern with different land uses, have been in evidence in the page 56), can indicate possible risk areas. Areas may area under investigation. have been abandoned for cropping for a number of reasons. To assess whether salinity was a factor, the Cropping (irrigated and dryland) suspect area should be analysed for landform and Clearing land for crops can contribute to watertable geological contributing features (see Landform feature and seepage salting when vegetation is removed identification page 39 and Geology page 42). which previously maintained the watertable at a depth below the soil surface where capillary rise was not Sources of information significant. Fallow periods and some minimum tillage treatments can enhance recharge to the watertable. There are a number of excellent sources of information However, because of soil and aquifer characteristics, on historical land use: salting may not appear in the landscape until 20 to 50 • Current and past landholders may be able to years after initial clearing. provide information about the history of the area, Under irrigation, the greater volume of water being the timing and effects of clearing such as the introduced to the system can raise the watertable and development of local springs, and changes in water lead to watertable and seepage salting. Under these level and water quality in bores or wells. conditions, salting may appear much sooner. • Sequential aerial photography—available from the 1940s in some areas and the 1920s in other areas— Salts in irrigation water can contribute additional is available from DERM and, in some cases, the salts to soils being irrigated, causing irrigation water RAAF. salting. This process can occur over periods of two to ten years. Increasing soil sodicity (which can result • Historical land use information relevant to the from using moderately to highly sodic water) also area under investigation may be listed with degrades soil properties. the Queensland Spatial Information Council, a computerised directory of land-related information. When cropping practices leave the soil surface bare • Landsat imagery (for large-scale investigations) is during periods of high rainfall or when the active available through Sunmap and other sources. growth period of the crop is too short to use the available water, the soil is vulnerable to erosion, • Local historical societies and published histories of contributing to erosion scalding on susceptible soils the local area often provide valuable information. during major rainfall events. When seeking information on land use over time and its effects, look for the following features in Grazing (irrigated and dryland) particular: As for cropping, when land is cleared for pasture, • information about the property itself, as well as vegetation is removed which previously maintained other properties in the same catchment, especially the watertable at depth below the soil surface. Salting those upslope from the property in question may appear 20 to 50 years after initial clearing. • types and time periods of land use and why a Grazing lands in susceptible areas can be at risk of particular land use (such as cultivation) was erosion scalding. When over-grazing in dry periods discontinued removes vegetation from the soil surface in areas • patterns of clearing—which parts of the landscape with sodic subsoils, the soil is vulnerable to erosion were cleared, and when scalding. Erosion scalding can also be seen around • patterns that indicate patchy growth or wet areas, watering points, depending on how many there are and relationships with the rainfall pattern and where they are positioned. • areas where dams or weirs may have been built, even if these barriers no longer exist.
88 Salinity management handbook Residential subdivision Subdividing rural land into rural residential blocks can contribute to salinity in much the same way as land clearing and irrigation. When the development is occupied, increased amounts of water and nutrients are introduced into the system via wastewater and septic systems. Reticulated water supplies to developments, particularly those not serviced by sewerage, enhance recharge to groundwater and the likelihood of watertable salting in susceptible landscapes. However, compensatory managements, such as managed tree planting, enhanced use of groundwater (instead of reticulated water) and spray irrigation of properly treated waste effluent on an appropriately sized area, will assist in limiting watertable rise. Roads and dams can become barriers to water movement or sources of additional water. Salting can occur upslope of roads and upstream or downstream of dams.
Practical example Data derived from aerial photographs (see Figure 51) depict the expansion of a salt-affected area in a small catchment in the Lockyer Valley. The salt-affected area on Darbalara Farm has reached an equilibrium size (following clearing) which fluctuates according to long-term rainfall patterns.
Figure 51. Development of salt scald in response to land clearing and rainfall pattern in a small catchment in south- east Queensland.
moving 5-year average rainfall variation from mean rainfall (%) extent of scalding (ha)
year
Salinity management handbook 89 90 Salinity management handbook Part C — Managing
13 Management issues
14 Vegetation management
15 Engineering methods
16 Irrigation management
Salinity management handbook 91 Chapter 13 — Management issues
Management decisions are rarely straightforward Of the water inputs, only the water entering the or clear-cut because of the range of factors and recharge area is available to be managed. The salt complexity of interactions that contribute to salinity concentration of this water is not readily amenable and determine management priorities: to management, but the quantity of the water can • The expression of salinity in landscapes results be managed by implementing strategies to reduce from complex interactions between land the proportion of water (rainwater and irrigation use and management, landscape hydrology, water) passing through the root zone. Reducing geomorphology, historic salt loads, and socio- water inputs, wherever feasible, to maintain the economic and environmental factors. watertable below the critical depth in the discharge • Because of the slow hydrologic response in area will have major benefits for the productivity of many landscapes, there is often a long lead time any vegetative management strategy for salt-affected between the expense and effort of implementing lands, providing the salt concentration is still within a management strategy and the subsequent the salt tolerance range of the vegetation. Other site enjoyment of the results. parameters, such as the volume of groundwater flow and the sodicity of the groundwater, will influence • In some situations, the cost of implementing final management options. management strategies or controls can be greater than the value of on-site benefits or cost of off-site To effectively manage for productivity in the medium- effects (although there is difficulty in assessing the to long-term in discharge areas affected by shallow full ‘cost’ of off-site effects). watertables, evaporation needs to be reduced, particularly where there is very limited seasonal • Property boundaries rarely encompass whole flushing of salts from the soil surface or the root zone catchments, and additional problems can occur by rainfall. If the water in this area can be reduced when areas where the salinity problem is ‘caused’ (by transpiration or pumping, or by interception and ‘expressed’ are controlled by different before reaching the discharge area) to lower the landholders. watertable, salt can be stored in the unsaturated area The first step in developing an integrated, sustainable at the bottom of the root zone where its effect is less management strategy is to thoroughly investigate the significant. Salt in the root zone will be flushed by processes and local factors contributing to salinity. seasonal rainfall. Causal factors which have not been investigated and The only other viable option is to physically remove identified can not be addressed comprehensively salt from the system. The option of discharging and effectively. (The section Investigating salinity saline water into streams is generally not an page 27 guides the reader through the options and acceptable practice. Another option, often not activities of investigating salinity and establishing an adequately addressed, is to remove water and salts understanding of local salinity processes.) by intercepting water moving in the transmission After investigating salinity on-site and considering zone. This interception option is only viable where the available options in the light of the landholder’s geologic features, soil conditions and water quality priorities, in the end the landholder must select a are favourable. ‘best bet’ approach. The best approach to watertable salting management is to view the water raising the watertable as a Management options potential resource rather than as a problem, so that A number of options for managing salt-affected the situation can be managed to the landholder’s net catchments are available. Not all options are advantage. Depending on local circumstances and expensive to implement; one of the most common water quality, this water can possibly be diverted and useful is ‘fence and forget’—fencing the area from for productive use elsewhere on a property or in a stock and spelling it while natural or introduced salt- catchment, to increase the productivity of existing tolerant vegetation becomes established, after which resource uses or develop new uses, increasing time the area may be suitable for limited or controlled revenue to the property and diversifying resource use. grazing.
92 Salinity management handbook Options for managing salted catchments, which can Integrated management be used individually or in combination with other options, include: strategies • continuing with existing management—managing Broadly speaking, there are four potential the land in its current state management approaches for salt-affected lands. Each • altering current management practices— of these approaches aims to achieve a hydrologic considering alternative land uses (such as changing balance between recharge and discharge areas: from cropping to pasture or trees), changing the • manage the existing situation grazing regime (such as resting areas by fencing • reduce recharge them off from stock, or utilising an affected area as • intercept water in the transmission area a gap feed rather than for continuous grazing), and modifying existing irrigation practices • increase water use in the discharge area. • selecting suitable vegetation species for planting Each of these approaches is listed in Table 41, along in specific areas—establishing salt-tolerant pasture with features of situations most suited to each grass species and fodder shrubs in salt-affected management approach and desirable management areas, growing deep-rooted perennials such as practices. This table is intended only to provide an lucerne or leucaena for fodder crops, considering indication of the most viable management options alternative crops, and planting trees to intercept for a situation at hand when management is initially water in transmission areas or to use water in being considered. In addition to the table, more recharge areas information on determining whether a particular • retaining native vegetation—allowing native forest management approach is appropriate for local or perennial vegetation to revegetate naturally in conditions is provided in this section. recharge or discharge areas, and limiting future In many situations, a combination of the four clearing of native vegetation on recharge areas approaches may be needed to formulate the best • implementing engineering options—installing salinity management strategy for local conditions and drains or pumps to dewater areas with high the available resources. Decision support tools such watertables, using drainage systems to disperse as property management models and benefit-cost water flow away from discharge areas, intercepting analyses (mentioned in Decision support resources water in the transmission area by draining or page 96) will assist in developing a balance between pumping, and using intercepted water of suitable different levels of control in each of the recharge, quality to irrigate crops or water stock. transmission and discharge areas. Selecting an appropriate overall management strategy The relative size of recharge and discharge areas will depend on: will determine, to some extent, which strategies may • the extent and nature of the salting problem be appropriate. In any catchment, there has to be a minimum rate of drainage below the root zone to • the characteristics of the area—climate, soils, achieve a significant excess resulting in watertable geomorphology, water quality, and so on rise. At minimum rates of drainage, vegetation • access to unaffected areas that are contributing to can often cope with any additional water in the the salinity problem (recharge and transmission landscape. This can be approximated to around areas) 0.001%. A maximum theoretical salt-affected area • economic issues, such as the comparative value is around 10% of a catchment on the basis that of the land and cost of implementing various the rate of evaporation from a discharge area can management practices accommodate around 10 or more times the annual • the landholder’s own particular desires and needs. recharge rate. Surface seepage can also remove water from a catchment. In practice, this 10% is exceeded Some strategies may be straightforward to in southern Australia where there are widespread implement while others may necessitate a complete regional shallow watertables. reorganisation of farming operations. Catchment boundaries frequently cross property boundaries, The guidelines in Figure 52 are based on the with the result that neighbours may have to work significance of the problem in the catchment. In cooperatively to effectively address the problem. Queensland, there are two nominal boundaries to the Intensive engineering works or extensive tree planting relative sizes beyond which salting is unlikely to occur. programs may have to be staged over a number of years to suit available labour or financial resources.
Salinity management handbook 93 Table 41. Suitable situations and desirable management practices for each of the major salinity management approaches. Desirable management practices for implementing each strategy are listed approximately in order of likely effect.
Management Situations most suitable for the management approach Desirable management practices approach Manage • landform features: basalt, catena, alluvial valley, stratigraphic, • set a high priority on maintaining existing dykes, confluence of streams vegetative cover situation • affected land not of high value or productivity • fence off affected areas and manage • controlling recharge areas too costly, or recharge areas much grazing pressures more productive than affected discharge areas • enhance amount of salt-tolerant • vegetation currently surviving on most of the affected area vegetation in the worst affected areas • existing vegetation can be enhanced and/or fenced to control grazing • stabilise area against erosion, but do • seepage on the affected area is fair quality water not prevent seasonal flooding where this • erosion not a problem, or erosion can be stabilised with would normally occur vegetation • improve surface drainage • downstream water quality not significantly affected by salting in • plant trees or other perennial deep-rooted the affected area vegetation that can handle salt and • salt load in the discharge area is moderately high waterlogging • watertable intercepts the soil surface seasonally or periodically Reduce • the catena landform feature • avoid summer fallow in summer rainfall recharge • recharge area clearly identifiable and available for treatment areas, and use double or opportunity • area experiences a winter rainfall pattern cropping if possible • shallow-rooted pastures are main vegetative cover in the • introduce deeper rooted or perennial recharge area species into the pasture mix • current cropping practices could be made more water use • incorporate agroforestry into management efficient • revegetate stock routes and along fence • rainfall periods not aligned with periods of high water use by lines and geomorphic boundaries crops • if leakage from ponded areas is • recharge rates high significant, reduce size of these areas • land value or productive value of the discharge area greater than that of the recharge areas • soil in the discharge area likely to be productive after the area is reclaimed—that is, groundwater in the discharge area not particularly sodic and soil structure not severely affected Intercept • landform features: basalt, catena, colluvia of former land Depending on water quality and depth to water in the surfaces, valley restrictions, dykes, confluence of streams groundwater: transmission • transmission area relatively well defined • pump with pumps or windmills from area • recharge area large and not well defined single or linked tubewells. (A total • groundwater is of acceptable quality minimum flow of around 2 to 3 L/s is • good aquifers identifiable in the transmission area needed for this option to be viable.) • aquifers suitable for pumping or accessible by tree roots • if water is good quality, intercept • pumped water can be discharged into streams, evaporated or groundwater and use to irrigate adjacent used for irrigation areas or to water stock • discharge area is under upward hydraulic pressure resulting • plant dense vegetation belts, using high from a confining clay layer and is thus much more difficult to water use species, in areas where these manage plants can access the groundwater • both recharge and discharge areas have high land values • construct subsurface drainage (for off-site • large quantities of water involved disposal) if water is of acceptable quality • major salt loads occur in the discharge area Increase • landform features: colluvia of former land surfaces, valley • revegetate the area with perennial, high water use in restriction, dykes, geologic faulting water use, salt-tolerant vegetation discharge area • recharge area diffuse and extensive • plant halophytic species in high salinity • recharge areas distant from the discharge area, or not under the areas control of the discharge area landholder • pump with pumps or windmills from • discharge area extensive single or linked tubewells. (A total • high economic value of the recharge areas, regardless of the minimum flow of around 2 to 3 L/s is comparative value of the affected discharge areas needed for this option to be viable.) • transmission area diffuse • construct subsurface and surface • finite salt loads exist in the discharge area drainage • groundwater is of generally acceptable quality, or groundwater • pump into evaporation basins is saline and using evaporative basins to evaporate the excess • if water is good quality, pump to irrigate water is cost-effective adjacent areas • waterlogging is an issue
94 Salinity management handbook Figure 52. Possible watertable salinity control options, Figure 53. Vegetation management options for recharge based on the relative sizes of recharge and discharge areas. areas based on soil depth and saturated hydraulic These options need to be considered in conjunction with conductivity (Shaw 1993). the text and information in Table 41 (Shaw 1993).
1 000 1 000 don’t bother with re-vegetation unlikely occurrence (regional issues)
100 deep rooted re-vegetation 100
re-vegetate recharge (mm/day) s K 10 active pasture intercept flow 10
manage as is water efficient cropping 1 size of discharge area (heactares) 1 unlikely occurrence 0 12345+
0.1 depth of soil plus weathered material 10 100 1 000 10 000 100 000
size of recharge area (heactares) Intercept water in the transmission Manage the existing situation area Water can be intercepted by revegetating key areas This approach is appropriate where the salted area is or by using engineering methods. If revegetating, of comparatively low-value land and natural processes groundwater needs to be present at depths that prevent excessive salt from accumulating at the soil trees can access. Revegetation is more likely to be surface. For instance, the soil surface may be flushed effective where water use by trees is likely to account on a seasonal basis by runoff or seasonal seepage. for a significant proportion of the flow. If the water The key to this management option is to maintain is of good quality, it can be reused elsewhere on the adequate (and appropriate) vegetative cover at all property for irrigation or stock watering. If aquifer times. Methods include fencing salt-affected areas properties and flow are suitable, water can be and allowing opportunity grazing, and allowing weed pumped from the transmission area using simple, low- or grass growth in cropping areas. technology, low-energy pumps. Reduce recharge Increase water use in the discharge To reduce recharge, significant areas of the upper area catchment may need to be revegetated with trees or well-managed native pastures, and agronomic Water use or removal by pumping, drainage and/or practices in cropping areas may need to be vegetation (with halophytes and salt-tolerant plants) substantially modified. Because recharge in many is an option on discharge areas depending on the salt tropical areas is episodic, planting additional load and the depth of clay overlaying more permeable vegetation to reduce recharge will only be effective materials. Drainage requires permeable subsurface where water use by currently grown crops is low during materials so that flow into the drains is adequate. the high rainfall season. Clay depth provides a measure of the extent to which water can be removed by vegetation or engineering Selecting appropriate vegetation options for recharge methods. Salt loads may be at shallow depths areas—whether or not to revegetate, whether to plant in some areas where upward hydraulic pressure trees, crops or pasture—largely depends on the level operates. Under these conditions, a finite salt load of annual recharge. Figure 53 illustrates vegetation exists that may be controlled by short-term high salt management options for recharge areas based on disposal or by managing the watertable level. soil depth and saturated hydraulic conductivity (as an indicator of recharge) which determine the length Figure 54 indicates the conditions under which of time during which water moving through the interception and vegetation can be considered as soil profile is available to plants. This needs to be management options, depending on clay depth and assessed only in areas with high flow ranges, shallow salt load as measured by an EM‑31 instrument (see soils over fractured rock, highly permeable soils or Landscape salinity mapping page 43). very slowly permeable soils.
Salinity management handbook 95 It is important that a drainage strategy does not lower Broadly speaking, the following need to be considered the watertable to a critical depth which will actually when contemplating salinity management decisions: result in an increase in the bare and salted area. In • financial issues, such as set-up costs, comparative regions where salts are seasonally flushed from the ‘value’ of amenity and aesthetics soil profile by periodic high watertables, lowering the • short- and long-term goals watertable to the critical depth for capillary rise can reduce the effectiveness of seasonal flushing. Surface • interest in diversification and alternative land uses concentration of salts will increase as a result. • personal attitudes to environmental responsibility Increased surface water flow from recently-installed • potential for impact of a management strategy on drains may enhance gully erosion. The impact of properties downslope in the catchment increased salt loads on downstream water users must • activities and attitudes of neighbours and local be considered, as well as environmental protection catchment management groups. and water quality legislation.
Figure 54. Incorporating vegetation and interception Benefit–cost analyses strategies in discharge areas (Shaw 1993). Benefit–cost analyses are invaluable when evaluating 400 management strategies. Important considerations are the cost of managing the current degraded situation, costs of management for partial control, and costs interception and/or halophytes of reclamation. For investigations of salinity risk 300 before land is developed, the cost of preventative management for the area predicted to be affected will be required. Other considerations are the value of interception and/or vegetation 200 the productive lands in the recharge areas that may be reduced by some land management options such as revegetation. Management costs need to evaluate on-site versus off-site costs such as increased salinity 100 vegetation and/or interception of water supplies or increased erosion of salted areas,
salt load estimated from EM 31 (mS/m) particularly in summer rainfall areas. drainage
0 Decision support resources 0 246810 Management decision support services range in scope depth of clay soil over more permeable material (metres) from catchment-scale to property-scale. Community groups (for instance, landcare and Integrated Catchment Management groups and committees) Management decision making help focus management strategies for salinity at the appropriate catchment scale. Using the principles Deciding how to manage a particular situation is rarely of Property Management Planning, management a case of simply choosing the option with the best decisions can be comprehensively worked through prognosis. Many other factors enter into the decision- from initial investigation to implementation, ensuring making process, and these factors will always depend the problem is thoroughly analysed and addressed on individual landholder priorities and constraints. and that a solution is determined that addresses Making salinity management decisions can mean the situation needs, is within the scope of available deciding between competing objectives, such as resources, and is consistent with personal and economic and environmental objectives. business goals and resource sustainability. While technical officers and other advisers provide With the increased number of stakeholders involved expertise for assessing how particular areas will and more complex assessments of natural processes respond to different types of management, the final available, decision making is now a complex process. responsibility for deciding what will be done, and Decision support system approaches are often carrying out these decisions, lies with the individual necessary to provide a focus for the issues to be landholders. resolved. Decision support systems can be defined (after Thompson et al. 1992) as ‘the integration of expert knowledge, management models and timely information to assist in making day-to-day operational and long range strategic decisions’. Key concepts
96 Salinity management handbook are the ability to evaluate ‘what if’ questions and carried out in the monitoring and evaluation phases. to predict the effects of decisions. Where there are The process is followed by a planning review phase many stakeholders and multiple solutions, multi- in which coordination is a priority issue. This process disciplinary approaches are required. is currently being used in a series of large catchments in Australia where integrated solutions to catchment- Because the rate of change in groundwater levels scale dryland and water salinity problems are being with time is often fairly slow, good predictions of sought. PRIME is a decision support process rather the possible long-term consequences need to be than a software-based decision support system. made. Models are often necessary to adequately integrate climate variability (particularly rainfall) The original AEAM (Adaptive Environmental and spatial variability. However, models are only Assessment and Management) concepts from tools to assist understanding. A scaled approach Canada as reported by Grayson and Doolan (1995) in model complexity is required. Where the issues have been used at a catchment scale in some areas can be identified in yes/no terms, simple ‘back of of Australia. The AEAM process aims to provide the envelope’ calculations and expert opinion may links between communities with a problem and suffice. Where the interactions between processes or the available technical resources. During a series managements are more complex, more quantitative, of interactive workshops, a computer-based model broad-scale and complex models with associated is developed that can evaluate the outcomes of greater data requirements need to be considered. various resource management options using the best In all cases, as the catchment increases in size the available technical information. The major benefits accuracy of predictions will decrease sharply. have been identified as the creation of a common understanding and ownership among stakeholders Catchment scale models, using well-developed and the development of a computer simulation groundwater models (for instance, MODFLOW) model using the best available information (Grayson and incorporating decision theory allowing ‘what & Doolan 1995). Disadvantages are the need for if’ situations to be evaluated, are currently being skilled modellers in structured workshops and developed by the Department of Environment and limited validation of the model except as a qualitative Resource Management and CSIRO. Detailed modelling comparison with informed technical opinion. AEAM is generally time consuming and expensive, and is is suitable for some (but not all) situations and only justified when other management investigations issues. Its usefulness depends on the time periods are inconclusive. (Useful modelling software packages of the processes and the extent to which catchment are listed in the Useful software packages page 141.) scale averaging of biophysical responses provides Multi-objective decision support systems specifically acceptable data. addressing natural resource management issues are A multi-objective decision support system (MODSS) is currently being developed. A wide range of agricultural available (prototype currently) that allows individuals productivity decision support systems are available. and groups to identify the issues, the stakeholders, The following three approaches, PRIME, AEAM the criteria and the importance ranking in order to and MODSS, address aspects of natural resource select the most appropriate option. The system will management issues appropriate for catchment scale produce a number of options together with a matrix salinity issues. of options against criteria to be rated from a range PRIME (Planning, Research, Implementation, of sources, data, technical experts and simulation Monitoring and Evaluation) is a procedure for models. Following decision optimisation techniques, developing Integrated Catchment Management the preferred options can be considered, discussed plans by stakeholder groups developed by Syme and resolved. Further information on MODSS can be et al. (1994). It is a staged decision framework. obtained from the Department of Environment and In the planning phase, the problem is defined, Resource Management. available knowledge collated, priorities formulated, objectives negotiated, gaps identified, the basic plan devised, and resources and criteria for evaluation and monitoring determined. In the research phase, feasible solutions from the literature and elsewhere are identified, barriers to adoption identified, and collaborative applied research programs developed. In the implementation phase, the implementation strategy is derived and resources determined and allocated for priority activities. Similar activities are
Salinity management handbook 97 Chapter 14 — Vegetation management
Vegetation can be planted (or retained) to manage rainfall areas. Species to be planted in recharge, water: transmission or discharge areas that are adapted for • by reducing recharge to the groundwater the general site conditions will improve the likelihood of survival and growth without requiring excessive • by intercepting water as it moves through the maintenance during periods when conditions are landscape unfavourable. • by increasing the rate of groundwater discharge. Recharge areas Vegetation in areas of the In recharge areas, trees and high water use crops can landscape reduce deep drainage by using more water to a greater depth (creating higher antecedent soil water deficits, Careful planning is the key to cost-effective treatment Morris and Thompson 1983) and by intercepting of salinity. Approaches integrating vegetation with more rain in the canopy than most pastures or crops, engineering works and modified farming practices are especially in winter rainfall areas. In summer rainfall most likely to be successful. areas, summer fallow and heavily grazed pastures will It is generally better to focus vegetation management result in increased recharge. Opportunity cropping on transmission and recharge areas than discharge and pasture systems which include some deeper areas. This is because the high salt concentrations rooted species will reduce recharge to some extent. in the soil and groundwater in discharge areas, The soil water available to plants in recharge areas often accompanied by seasonal waterlogging and is not usually saline and thus the normal species the presence of sodic soils, create unfavourable selection factors for local site conditions will indicate conditions for plant survival and growth. The the long-term growth of the chosen species. Ideally, effectiveness of increasing vegetative extraction species with high water use capability are preferred. of saline groundwater in the discharge area alone (without reducing recharge) is limited because: Factors to be considered in selecting species for recharge area plantings are: • it is difficult to establish plants in saline environments • site conditions—rainfall, risk of frost, exposure to winds and sun, soil types, existing vegetation, • the rate at which plants use water depends on the original vegetation type stress they experience • species water use capability • the amount of water supplied by the comparatively extensive recharge area will usually be far in excess • in the case of trees, multiple use considerations— of the transpiration capacities of vegetation planted possible use for timber production, stock shade on the discharge area, even if all the vegetation or shelter, windbreaks, wildlife habitat, or tree were using water at the optimal rate products such as honey, bush tucker, flowers, oils or seed. • special management of the area will be required for long-term stability Figure 55. Recharge area plantings in a salt-affected • the removal of water by transpiration may increase catchment near Yass, New South Wales. soil salinity levels and aggravate the problem of insufficient water use (Morris & Thompson 1983; Thorburn et al. 1986). Vegetation in the discharge area is appropriate for managing erosion and maintaining some productivity. Unless the supply of water to the discharge area is reduced, a permanent reduction of the problem is not likely to be achieved by vegetation in the discharge area alone. The information in the following sections on species selection applies generally to selecting pasture, crop and tree species for managing salinity in summer
98 Salinity management handbook Transmission areas productive use of the site. Naturally saline soils support a diversity of species, some of which are Transmission area plantings can be an effective option useful agronomically. If vegetation strategies are well when good quality groundwater is moving through planned and managed, saline soils can be productive. the landscape in a zone accessible to plant roots. For instance, access by plant roots to the groundwater Figure 56. Tall wheat grass and Rhodes grass in a discharge should not be impeded by structures such as hard area on the Darling Downs, Queensland. pans or other geological formations. If groundwater in the transmission area is saline, transmission area plantings may be ineffective. Water uptake is likely to decrease over time as salt becomes concentrated in the root zone, thus reducing the effectiveness of vegetation in removing groundwater. A rough calculation of catchment water balance is needed to see if the area planned for revegetation can use sufficient water. (Calculating catchment water balance is described in Catchment groundwater balance estimation page 70.) Conditions in transmission areas are often similar to those in recharge areas, possibly with higher levels of groundwater salinity. In some cases, transmission areas can have more favourable conditions for vegetation establishment than recharge areas because of better groundwater supplies or better soils on lower slope positions. Species should be chosen on the basis of high water consumption capacity and the ability to cope with moderately saline groundwater (if present) and saline soils (which may occur over time). Multiple uses of trees would be important secondary considerations. Consideration could be given to species that can be irrigated with low to moderate salinity groundwater Factors to be considered when choosing species supplied by groundwater pumping. for planting on discharge sites, usually very harsh environments, are: Discharge areas • adaptation to the general site conditions • salinity tolerance As discussed previously, vegetating discharge • sodicity tolerance areas effectively can be difficult. However, planting discharge areas with salt- or waterlogging-tolerant • tolerance to poor soil drainage or waterlogging vegetation can be important when recharge areas • frost tolerance are hard to identify, difficult to manage or revegetate • water use capability sufficiently to control recharge, or unavailable for • potential for multiple use (in the case of trees). management (for instance, if the recharge area is on another property). These factors often occur in combination, and this usually has a compounding impact on vegetation, Discharge area plantings provide an opportunity for young plants in particular. A more restricted range bringing an area of land back into productive use. of species is likely to be available and opportunities Many landholders prefer to focus remedial vegetation for multiple use will be limited as plants are unlikely activity on the unproductive salted sites rather to perform well under highly saline or waterlogged than to place productive agricultural uplands under conditions. alternative vegetation. Combined with other planting or engineering works, General site conditions discharge area plantings may lower the watertable Adaptation to climate, soils, aspect and other factors sufficiently to prevent further concentration of salt has to be considered more carefully when choosing on the soil surface by evaporation and to allow plants for the adverse conditions of discharge areas leaching of surface salt by rainfall, enabling more than for areas with favourable growing conditions.
Salinity management handbook 99 Figure 57. Tree planting on a scalded discharge area near Tolerance of poor soil drainage or Kingaroy, Queensland. waterlogging Species adapted for dealing with poor drainage or waterlogging will usually be more successful in discharge areas. Some species can tolerate seasonal waterlogging, sometimes for many months, but many species are highly intolerant of these conditions. Waterlogging usually reduces the ability of plants to tolerate saline conditions (Marcar et al. 1991), so species that can survive a combination of salinity and waterlogging are often required. If watertables are consistently high, trees may form very shallow root systems, making them susceptible to windfall.
Frost tolerance Saline discharge areas usually occur in the lowest parts of the landscape, where there is poor drainage of the cold air. If frosts occur in the area, frost-hardy species may be required.
Water use Water use capability is an important factor when selecting species for discharge areas. However, in harsh conditions this factor will be secondary to selecting species that can survive on the site. Tree Salinity tolerance spacing and management can be used to some extent Many plant species are unaffected by relatively low to affect the amount of water use in a planted area. soil salt concentrations. Some species can withstand Water use is determined by species, climate and local moderate or high salinity levels. Relatively few species environmental factors. are able to tolerate very high levels of salt. Even where a species can survive in saline conditions, growth Multiple uses rates and resistance to disease may be severely The economics of saline site rehabilitation improve retarded. substantially if financial returns can be obtained from If irrigation with groundwater is proposed, a species’ trees used in the rehabilitation process. ability to tolerate irrigation with saline water may also If suitable matches can be made between tree need to be considered. species, site conditions, products and services, and good integration can be achieved between agricultural Sodicity tolerance enterprises and tree management systems on the Many saline sites are also sodic. Plant species vary property, a high economic return can be obtained in their ability to tolerate sodic soils. The major from landscapes supporting a large percentage of constraints to plant growth in sodic soils (Marcar et al. tree cover. Trees may also contribute services to the 1993) are: farm in terms of wildlife habitat, shade and shelter for crops and stock, and aesthetic value. • poor physical conditions and correspondingly poor soil aeration when wet • nutritional imbalances including deficiencies of General site treatment trace elements Many pasture, crop and tree species are most • specific ion toxicity (such as sodium, chloride or sensitive to salinity at germination and during possibly boron). establishment. Even species able to grow in extreme levels of soil salinity, such as saltbush, normally germinate and establish only after rain has flushed salts from the soil surface. Soil preparation methods and activities that reduce surface salt levels and promote plant growth are therefore vital for successful establishment of plants in saline environments.
100 Salinity management handbook Vegetative cover Vegetation options In almost all areas susceptible to salting, the A number of factors need to be considered when vegetative cover of the soil surface needs to be deciding whether and where to use crops, pasture or maintained and the soil surface not laid bare by trees to manage salinity: cultivation or overgrazing. Where salting is associated • landholder’s goals—importance of initial cost and with a shallow watertable, removing vegetation from final financial return, time available to manage the soil will lead to the surface accumulation of salts. • individual area characteristics—water source, In areas susceptible to scalding, a bare soil surface water quality, landscape feature to be planted, soil will be vulnerable to erosion processes, soil loss and characteristics, soil salinity and sodicity levels soil degradation. • individual species characteristics—salt tolerance, Mulching is beneficial because it reduces water use, rooting depth, time to establishment, concentration of salts at the soil surface and aids likely productivity plant establishment. • time frame before a response will be evident— interaction between climate (period of dominant Grazing and stock control rainfall) and time to establishment of species. Grazing and pest animals must be controlled by fencing or low stocking rates for pasture or tree Pasture planting or regeneration to be successful. In many cases, grazing control alone on the affected area and The following situations are more suitable for pastures margins is sufficient to allow salt-affected areas to than cropping: revegetate successfully. Costs include the cost of • low-value land fencing and loss of amenity of the fenced-off area. • strongly undulating country or steep slopes Benefits include preventing the spread of the salting • soils of moderate to high permeability problem and being able to use the area again to some • where soil acidity is not a limiting problem extent after revegetation. • where deep-rooted or perennial grasses are viable Water movement control • if grazing gives viable returns • if grazing control can be effected The areas to be reclaimed should be protected from • when agroforestry is an option runoff water. A diversion bank can be used to direct water to more stable areas. Planting is best carried out • when climate and/or water resources favour at the beginning of the wet season when watertable pastures. levels are lowest and early rains have flushed salt from the surface. Crops Few traditional crops can be grown on saline soils. Mounding High water use crops can play a role in recharge If the soil water is saline, trees, crops and pastures control. Situations most suited to using crops to planted on the tops of standard mounds can be manage salinity include: affected by evaporative salt accumulation at the high • soils of moderate to high fertility and low salinity point of the mound. This effect can be minimised by • soils with good plant-available water capacity using mulch, constructing broad mounds, and setting • soils have moderate to high clay content the plants off the top of the mound. Seedlings planted in the trough of M-shaped mounds are less likely to be • soils have low to moderate hydraulic conductivity affected by salinity because salt will accumulate in the • soil erosion can be controlled peaks to either side of the trough. • areas suitable for cultivation There is mixed evidence on the benefits of forming • where opportunity cropping in wetter years is an mounds some time prior to planting. In M-shaped option mounds, water collecting in the trough of the mound • where cropping practices, including fallow may leach some salt from the soil. However, capillary practices, can be managed to minimise recharge. action and evaporation from the increased bare area of soil may bring additional salt into the mound. In standard-shaped mounds constructed prior to planting, salt accumulation in the mound can be a problem if insufficient rain falls to leach salts. Soil leaching can be achieved without salt accumulation if the mounds are mulched.
Salinity management handbook 101 Trees Forage shrubs such as saltbush can raise the feed value of mixed pastures on saline soils. Saltbush, Under favourable conditions, trees can extract large bluebush and related plants have been considered a quantities of water from the soil by transpiration and valuable stabilising component of grazing pastures can directly intercept and evaporate rainfall. Trees in arid and semiarid areas of Australia for many years actively use water for a greater part of the year than because of their ability to maintain green leaf through most crops and pastures. When planted in recharge seasonal dry spells and droughts. Closer to the coast, areas, trees use more water to a greater depth in the these species are valuable for grazing during dry root zone than shallower rooted species, reducing periods, as their protein levels are maintained when deep drainage. When planted in transmission other feeds have hayed off. It is necessary to have and discharge areas, some tree species can draw alternative feeds available (crop stubble, grasses) water directly from the groundwater. However, less to dilute the high salt content of the shrubs. Some than favourable conditions in discharge areas are species do not tolerate waterlogging. Species which not optimal for timber production. Trees may also are known to grow well on saline soils, be palatable to contribute less directly to salinity control by: stock, and withstand grazing pressures are indicated • providing shade and shelter on discharge areas, in the table in the appendix Pasture species for saline and reducing surface evaporation rates and the rate soils (page 133). of concentration of salt at the soil surface Samphires and glassworts are valuable in areas where • assisting to reduce the risk of wind and water extreme salinity and regular waterlogging prevent erosion on scalded sites by acting as windbreaks, the growth of other plants. The protein content of providing a litter mulch, reducing raindrop energy samphire is high, but intake is reduced by salt levels and binding the soil with root systems. of about 20% dry weight of chloride. These species Situations most suited to using trees to manage may improve soil conditions such that other, less- salinity include: tolerant species can establish through them. • shallow soils over weathered and fractured rock • deep sandy or permeable soils Pasture establishment and • steep and broken country maintenance • where timber processing industries are situated nearby Pasture cultivation • when shade or windbreaks are needed Shallow cultivation is normally sufficient to establish pasture species and grasses. Deep ripping and • when wildlife protection is desired agroplough are only justified if significant yield • if agroforestry is an option. improvement is obtained as a result. It is not always necessary to spray or burn existing weed species to Pasture allow desirable species to establish successfully. In most saline areas in Queensland, heavy grazing of A variety of palatable and nutritious forage plants can the area prior to planting will be sufficient to reduce be established on saline soils provided appropriate competition. species are selected and management regimes adopted. Pastures on saline areas are most valuable Pasture planting if crash-grazed followed by a long spell. This allows Many of the grasses used on salt-affected soils in pastures to recover and the salt-affected area to be Queensland can only be established from rooted utilised as a gap feed. clumps or turf. A sprig planter can be used for planting grasses such as marine and saltwater couch. If Pasture species planting by hand, a shallow hole should be dug into Grasses useful for waterlogged and saline which the grass clumps are pressed. conditions in Queensland are listed in the appendix For species to be introduced by seed, shallow Pasture species for saline soils (page 133). The cultivation of the soil surface to dilute salts through legumes Medicago sativa cv. Sirosal, M. scutellata, the top few centimetres of soil is generally sufficient M. truncalata, Macroptilium lathyroides, M. for establishment. Pioneer Rhodes grass establishes atropurpureum and Trifolium fragiferum tolerate mild well from seed on highly saline soils; more palatable salinity but are usually more difficult to establish species included in the seed mix may be able to (Russell 1976; Fisher & Skerman 1986; Runciman establish after Pioneer Rhodes. 1986). With all of these species, local suitability must be assessed.
102 Salinity management handbook On flat ground, a conventional combine without Grazing control harrows can be used to provide variety in the soil Stock should be excluded for at least 12 months and surface. A scarifier can be useful immediately prior up to two years after salt-tolerant species are planted. to sowing on highly saline soils. Seed is spread on Such areas can be grazed subsequently for short the surface. On steep slopes, where cultivation is not periods of time. Saltland pastures are most valuable recommended because of the risk of erosion, direct when used as a feed reserve when other pastures are drill seeding may be appropriate provided the seed in short supply and spelled for the remainder of the is not buried too deep. If machinery access is not year. practical, for example on waterlogged sites, spreading seed by hand on the soil surface is sufficient. Saltbushes can be established from either seed or Crops nursery-raised seedlings. Success rates are much In recharge and transmission areas, crop type and higher if seedlings are used, but costs also increase. cropping systems should be selected to maximise Double ridge or M-shaped mounds (discussed in water use and minimise fallow and dormant periods. Mounding page 101) are advisable to flush salts from the root zone of the young seedling to reduce As with pastures (previous section), it is appropriate transplanting shock. Mounds are also recommended to limit discussion here to cropping on marginal and for spot placements of seed covered by a mulch such salt-affected soils. Choosing crop species for recharge as hay or vermiculite. The Mallen niche seeder can be and transmission areas will relate more to soils and used for this purpose (Malcolm & Allen 1981). climate that to salinity as such. Optimal plant spacing varies between species; On marginal soils, cropping can be viable if spacing should allow for sufficient grass growth appropriate species are selected and careful between the bushes to provide a balanced diet. management is practised. Extensive breeding River saltbush (Atriplex amnicola) is best planted programs have been conducted in an attempt to raise at 1000 plants/ha, whereas grey saltbush (Atriplex the salt tolerance of many crop species, but results cinerea) is best planted at 125 plants/ha. Saltbush have been largely disappointing. This is because productivity can be improved significantly by using traditional food crops, other than beets and date an agroplough and a nitrogen fertiliser such as DAP palms, are not halophytic and thus have relatively low (Barrett-Lennard 1993). salt tolerance. Samphires are best established from seed sown on the surface (Malcolm & Cooper 1974). Seed can Crop species be spread by harvesting plant shoots soon after The levels of soil salinity tolerated by a range of seeding and spreading these pieces. Coastal pigface crops are listed in the table in the appendix Plant (Sesuvium portulacastrum) establishes well from salt-tolerance data (page 124). Alternatively, plant pieces (Townson & Roberts 1992). this information can be obtained by using the SALFPREDICT component of the SALF software Fertilising package (see page 142). Species selected to tolerate To improve the condition of low sodicity/high salinity the highest expected levels of salinity will be likely to soils, gypsum can be applied before cultivation at a produce the best yields. rate of 5 to 7 t/ha. However, if high levels of soluble It is also important to recognise that salt tolerance salts are also present, gypsum will have little effect. varies with the growth stage of plants. Some species Gypsum is recommended for clay soils with low are more salt tolerant at germination and emergence salinity. Early in the following growing season, the than after establishment. Table 42 lists the relative area should be top-dressed with complete fertiliser salt tolerances of a number of species for emergence 4:4:1 of NPK at 125 kg/ha. Local extension advice will versus yield. The salinity values provided can be be available on general fertiliser use. equated to salinity measurements at the planting depth in normal soils. While 50% yield and 50% Mulching emergence are used for comparative purposes, Mulching normally promotes grass establishment in cropping is not economically viable at these levels salt-affected areas. Hay, straw or manure can be used. of reduction. Grass hay is normally more suitable than cereal hay as seeds of undesirable species in grass hay are less likely to survive under saline conditions.
Salinity management handbook 103 Table 42. Relative salt tolerance of various crops at emergence and during growth to maturity (from Maas Tree planting 1986). Used with kind permission of E.V. Mass. Using trees to manage salinity is a long-term strategy. After trees are planted, it will be some years before 50% 50% watertable levels start to be affected and many years Common yield Scientific name emergence* before the trees reach maturity and provide other name ECse ECse (dS/m) desired benefits. The use of trees in salinity control (dS/m) should be consistent with property management Grain crops aims and objectives and be integrated with other Barley Hordeum vulgare 16–24 18 farm management activities so that the trees can be Corn Zea mays 21–24 5.9 properly managed and maintained in the long term. Cotton Gossypium 15 17 Trees can be used to enhance the farm environment, Rice Oryza sativa 18 3.6 boost returns from established enterprises and Safflower Carthamus provide opportunities for diversification into forestry 12 14 tinctorius or forest products. Sorghum Sorghum bicolor 13 15 Figure 58. An example of tree planting equipment utilised Wheat Triticum aeativum 14–16 13 for large scale revegetation projects. Heavy vegetables Beet, red Beta vulgaris 13.8 9.6 Onion Allium cepa 5.6 4.3 Sugarbeet Beta vulgaris 7.5 15 Pasture spedes Cowpea Vigna unguiculata 16 9.1 Lucerne Medicago sativa 8–13 8.9 Vegetables Bean Phaseolus vulgaris 8 3.6 Cabbage Brassica oleracea 13 7.0 capitata Lettuce Lactuca sativa 11 5.2 Tomato Lycopersicon 7.6 7.6 lycopersicum
Crop establishment and maintenance In saline areas, evaporative concentration of salt on the soil surface or in the upper root zone is the most likely cause of poor crop response. Maintaining any Shade and shelter produced by trees can improve amount of stubble on the soil surface will help to growth rates in stock, increase calving and lambing reduce evaporation. Minimum tillage practices and percentages, extend the availability of pasture in seeding into previous crop residues can also help to times of drought or frost, and reduce soil-water reduce evaporation. consumption by crops (Bird et al. 1991; Daly 1984; By planting into the trough of M-shaped ridges or Roberts 1984). Use of Acacia spp. on discharge sites into the side of single-humped ridges, plants can or fodder species such as leucaena on recharge areas be separated from the ridge peaks, where maximum can provide high protein browse for stock, increasing evaporative salt concentration occurs (see Mounding productivity compared with pasture alone. page 101). However, if these practices are necessary, it Many tree species produce valuable timber and wood may be more economically viable to move from crops products such as firewood, fencing timber, poles and to pasture. sawlogs for structural or decorative purposes, veneer Periodic irrigation to flush salts from the soil surface logs, and craft timbers. Many Eucalyptus and Acacia can effectively reduce salt loads where soils are species suitable for salinity control are premium- permeable and watertables are deeper than about quality structural and appearance-grade timbers. 0.5 m. Some species of eucalyptus, tea tree and brush box are sought by beekeepers because of the excellent
104 Salinity management handbook honey produced. Other tree products are fruits and in departmental nurseries, provides comprehensive nuts, oils, substances for medical use, flowers, bush information on the characteristics and tolerances tucker and seed. Mallee and Melaleuca species can of a wide range of species. A computerised species be harvested for oil production. By selecting a diverse selection system, the Tree Selection Module, is also range of tree and shrub species for windbreaks and accessible at departmental offices. shade, a variety of food sources and nesting and Table 43 is an abbreviated listing of tree species shelter opportunities can be provided for native bird, specifically recommended for discharge sites. A more mammal, reptile and invertebrate species. comprehensive list, detailing salinity and waterlogging Costs associated with tree planting generally include tolerances and suitability for multiple uses, is costs of tree establishment (fencing, site preparation) provided in the appendix Tree species for salinity and maintenance, costs of lost agricultural production management (page 137). on the planted area, and cost of time spent away Table 43. Trees and shrubs recommended for planting on from other farming activities. Benefits of tree planting waterlogged and/or saline discharge sites in Queensland. include returns to the landowner as well as to the community. Community benefits are in the form Suitable for of reduced impact on downstream water quality, sites that increased habitat values and improved salinity control are on neighbouring properties. Common Scientific Where trees are planted (or maintained) primarily name name to prevent or combat land degradation, such as to control salinity, stabilise erosion gullies, and establish saline frost-prone windbreaks to prevent soil erosion, associated costs water-logged may have tax advantages. If trees are planted for Trees the purpose of producing timber, associated costs are deductable as business-related expenses. Re- Belah Casuarina cristata 3 3 3 subdivision of the property according to land types is Casuarina River sheoak 3 3 3 also deductible if it is carried out in accordance with cunninghamiana an approved farm plan. Beach sheoak Casuarina equisetifolia 3 3 3 Appropriate reforestation layouts and attention to the choice of species can ensure that an optimal Swamp Casuarina glauca 33 33 3 economic return is achieved. Comprehensive sheoak economic analysis of farm operations, comparing Chinchilla Eucalyptus argophloia 3 7 3 the status quo with strategic options, will allow the white gum most economically efficient strategy to be selected. River red gum Eucalyptus camaldulensis 33 33 3 Computer-based models can facilitate this analysis. Tallowwood Eucalyptus microtheca 3 7 3 Department of Employment, Economic Development Grey box Eucalyptus molucanna 3 7 3 and Innovation officers are able to provide further Swamp information on costs and benefits to incorporate into Eucalyptus robusta 3 3 7 mahogany analyses of growing trees for managing salinity. (Refer Forest red also to Decision support resources page 96.) Eucalyptus tereticornis 3 3 3 gum Broad-leaved Melaleuca leucadendra 3 33 7 Tree species tea tree Broad-leaved Vegetation on the site and remnant native vegetation Melaleuca quinquenervia 3 33 3 on similar sites in the area can indicate suitable tea tree species. However, if there have been extensive Shrubs (<10 m) changes to the landscape (clearing, modification River cooba Acacia stenophylla 3 7 3 of soils by pasture improvement, cultivation or the Leptospermum polygali- Tantoon 3 3 3 addition of fertilisers), local species may no longer be folium the most suitable. (General information applicable Leucaena Leucaena leucocephala 3 7 7 to choosing tree species as well as pasture and crop River tea tree Melaleuca bracteata 3 33 3 species is covered in some detail in Vegetation in Totem poles Melaleuca decussata 3 3 7 areas of the landscape page 98). Prickly-leaved Melaleuca nodosa 3 33 3 Species selection advice is available from Department paperbark of Environment and Resource Management (forestry) Thyme Melaleuca thymifolia 3 3 3 nurseries. The booklet Trees and shrubs (Queensland honeymyrtle Forest Service 1991), a catalogue of plants available
Salinity management handbook 105 Tree establishment and maintenance such as engineering methods, to reduce groundwater recharge or to intercept water before it reaches the Site planning discharge area. The tendency of trees to concentrate salt in the root zone is likely to be a problem only In most situations, a mixture of recharge, discharge in low rainfall areas where insufficient rain falls to and transmission area plantings will be required if periodically flush salt from the soil profile. trees are to be used in salinity control. Layout must be planned considering the hydrology and stratigraphy Site preparation of the site, salinity, waterlogging, soil fertility and opportunities to integrate tree plantings with other Under normal conditions, cultivation benefits young property enterprises or to obtain products and trees by improving root penetration and water benefits directly. The cost of fencing off young trees infiltration and controlling weeds. However, on from stock (which is potentially considerable) can be waterlogged sites, cultivation can exacerbate the reduced by integrating planting patterns with existing waterlogging problem because heavy machinery fencing layouts, if possible. compacts wet soil. On well-drained sites with clay subsoils, deep ripping can be useful to improve soil Options for recharge area plantings range from drainage and root penetration. The best time for deep broad-scale revegetation of a significant proportion ripping is winter or spring (as late as possible in the of the recharge area to intensive plantations of high dry season) when the ground is least waterlogged water use trees on high recharge areas. Optimal and soils are at an optimal moisture content for performance will be obtained by planting trees at a penetration and shattering. Rip lines should be density that allows each tree to develop a full canopy strip sprayed with a combination of knockdown and with a high leaf area index and an extensive root residual herbicides. system. This suggests that wide-spaced agroforestry plantings may be very effective in grazing areas, while Gypsum can be added to improve soil permeability linear windbreaks may be appropriate in cropping during tree establishment in areas with clay soils, and mixed farming areas. To bring the area back into poor soil drainage or waterlogging, or high pH or agricultural production relatively quickly, trees can sodicity levels. be planted densely to lower the watertable and later Mounding benefits tree survival and early tree growth thinned to allow pasture to establish. Widely spaced on most saline and/or waterlogged sites. M-shaped large trees with well-developed root systems continue mounds (with a small indentation along the top) are to use water at a high rate because of good air flow generally better for alleviating salinity problems, around the tree crowns. and standard (single-humped) mounds are better for The optimal amount of area for tree planting will waterlogging problems (see page 101). Surface drains vary from site to site, depending on local rainfall (furrows) formed while creating mounds (see above) and aquifer characteristics. However, evidence from should be aligned to maximise surface water drainage Western Australia indicates that replanting less from the site. (Drainage is discussed in Engineering than 15% of the recharge area is ineffective, and methods page 110.) that effectiveness is directly proportional to the area Initial tree survival and early growth is likely to be planted. Increasing effects have been observed from improved if, prior to planting, salt can be leached from planting larger proportions of cleared recharge areas, the soil (for instance, by using drip irrigation or plastic with the effect being proportional to the area of land mulch on M-shaped mounds with holes punched for replanted (Schofield 1991). However, this is likely planting positions) without adding to waterlogging to be highly variable depending on groundwater problems. Other methods of reducing topsoil salinity, hydrology and rainfall characteristics and the results such as mixing saline topsoil with less saline subsoil cannot be extrapolated to areas with different using deep cultivation, adding less saline soil to conditions. planting holes, or mixing organic matter with saline In transmission areas where conditions are suitable, topsoil, appear to provide limited benefit and are not intensive plantations or belts of trees may be a cost- cost-effective. effective way of removing groundwater without using the large areas of land needed for recharge area Tree planting plantings. On moderately saline sites with good drainage, the In discharge areas, tree planting is only appropriate best time to plant is most likely after early summer where revegetation of a large enough area to use rainfall has provided sufficient soil moisture. Planting considerable amounts of groundwater relative to at this time will maximise growth during the available that flowing into the area can be achieved. In many growing season and provide shading and soil cover in cases this may mean using discharge area plantings the shortest possible time. In areas prone to seasonal in conjunction with other management strategies, waterlogging, planting should be carried out as soon as the area ceases to be waterlogged following
106 Salinity management handbook the end of the wet season to allow the seedlings Slashed or graded fire breaks 5 to 10 m wide should maximum time to become established before the be maintained around planted areas. Slashing next wet season. On severely salt-affected sites, the between rows of trees will minimise damage if fires optimum time to plant may be after a period of high do occur. rainfall which will have flushed some salt from the soil surface and upper soil profile. Tree retention Survival can be improved by preconditioning seedlings to site conditions such as waterlogging and Retaining existing native vegetation plays an salinity. Gradual exposure to increasingly waterlogged important role in limiting the occurrence or expansion conditions in the nursery appears to be the most of salting in salinity-prone catchments. effective part of this preconditioning. Land clearing in susceptible catchments should Fertilising is generally recommended for tree planting be undertaken only with extreme caution, and only projects, but good weed control is essential. At after the costs, benefits and risks of the venture planting, 100 g of DAP or an equivalent N–P fertiliser have been carefully considered. Small differences may be applied to each seedling. However, as in deep drainage are all that is needed to alter the stressed trees growing on waterlogged or saline hydrological cycle sufficiently to result in salting sites may be less able to utilise additional nutrients, or seepage problems. Long-term and very detailed fertiliser should generally only be added when trees studies would be required to detect such changes are not suffering waterlogging or salinity stress. (Scanlan 1991). Mulching improves tree survival, increases growth There is little point in clearing marginally economic rates, improves soil moisture conditions and reduces upland recharge areas if subsequent salinity in salinity levels in the soil beneath mulch. The choice discharge areas takes fertile lowland areas out of of mulch will usually depend on availability and cost. production. Revegetation programs are considerably Effective material for mulch is sometimes available as more costly than retaining the land in a naturally a by-product of other farming activities. vegetated state. Planning for clearing in the context of a Property Management Plan will ensure that Trees need to be watered well at the time of planting decisions will take into account all aspects of farm as for any planting project. Enhanced growth rates, activities, including natural resources, finances, improved productivity and more rapid lowering of management implications and personal goals. watertables may be achieved if tree plantings can be irrigated with suitable quality groundwater. In some cases, stands of native vegetation can be used to generate a financial return in their own right. Tree maintenance Managing stands of eucalyptus or cypress pine for commercial timber, farm timber or craft timber could Fencing to control animal access is critical on saline provide a return at least equal to grazing if clearing, sites, both to prevent browsing damage by grazing regeneration and land degradation costs are taken stock or feral animals while trees are young and to into account. Other enterprises based on remnant control grazing of pastures on the site in the long vegetation include opportunities for farm tourism, term. honey production and native food and seed collection Trees stressed by growing in waterlogged or saline (also discussed in Tree planting page 104). conditions are vulnerable to insect attack. The severity of insect attacks can be reduced in some instances by revegetating additional areas in the vicinity of the Guidelines for retaining trees areas being treated for salinity. Insect pest problems General guidelines for retaining trees in areas will be minimised if a diverse range of native species susceptible to salinity to minimise the risk of salinity is planted in an area to maximise the variety of occurring or expanding are provided in Table 44 and habitats available. the process for obtaining the necessary information to apply these guidelines is described in this section. At Control of weeds (including grasses and pastures) all times, decisions to retain or clear trees based on around trees for a distance of about 1.5 m from these guidelines need to be made in conjunction with the base of the tree for the first 12 to 18 months is all other tree retention/clearing guidelines, legislation generally necessary for good tree survival and growth. and limitations. There are many reasons for retaining Weed control options include cultivation, hand vegetation other than for salinity control, such as weeding, mulching and the use of knockdown and biodiversity, erosion control, aesthetics, wildlife residual herbicides. habitat, net increase or decrease in productivity of the land and so on.
Salinity management handbook 107 Table 44. Guidelines for retaining native vegetation, based on the results of local salinity investigations in Queensland.
Results of investigations in Level of Recommendation potential salinity indicator area salinity risk Any current surface expression of salting very high Retain all trees in the indicator area, immediately downslope from the indicator area, and upslope from the indicator area to the top of the landform. Any two of these high-risk indicators: high Retain all trees in the potential discharge area, • vegetative indicators of wet or saline areas immediately downslope from the potential discharge area, and upslope from the potential discharge area to • watertable depth less than 5 m below the surface the top of the landform. • evidence in the top 2 m of the soil profile of: • gleying • mottling • bands of CaCO3 nodules (other than at the bottom of the root zone) • abundance of iron concretions or staining • abundance of manganese concretions or staining • groundwater EC > 5 dS/m • EM‑31 reading > 150 mS/m • evidence of periodic seepage Any one of the high-risk indicators listed in the section medium Firstly, retain all trees in the potential discharge above, or any of the following indicators: area. Secondly, investigate the salinity risk of the • EM‑31 reading between 100 and 150 mS/m landform further to assess the extent to which trees should be retained in the area upslope from the • incised drainage line < 2 m deep potential discharge area to the top of the landform • any indicator approaching the level specified for the (in conjunction with other tree retention/clearing high-risk indicators listed in the section above guidelines and limitations). None of the indicators listed for high or medium risk low Plan tree retention/clearing decisions in conjunction with tree retention/clearing guidelines and limitations other than those for salinity risk. Note: Salinity may still occur in low-risk areas if subsequent changes in land use modify the hydrology of the catchment.
Firstly, all sites that may be currently salted or that Secondly, if these investigations indicate salinity, or if appear to have potential for developing salinity need more comprehensive investigations are warranted on to be investigated. These sites will be apparent on the a catchment scale to identify areas with the potential basis of: to develop salinity, the search should be widened • any evidence of salinity at the surface to include other areas in the catchment with similar characteristics to the sites already investigated, as • presence of vegetation communities or species well as the following areas: which indicate saline or wet areas • potential discharge sites of local landform types at • evidence of current or periodic seepages at the soil risk of salinity surface or in the soil profile • low-lying and break-of-slope areas • depth to watertable of less than 5 m. • other suspect areas based on unusual soil or Investigations at these sites should include, as a vegetation conditions, or areas that are prone to minimum: erosion. • salinity of the groundwater Thirdly, the recommendations in Table 44 are • salinity of water in drainage lines nearby guidelines for retaining trees based on the results of • soil profile characteristics to a depth of 2 m or to these site investigations. If no potential discharge the parent rock, in particular looking for gleying, sites occur in the catchment, salinity risk is likely to
CaCO3 nodules, or iron or manganese concretions be low, and decisions for retaining or clearing trees or staining should comply with tree retention/clearing guidelines • if possible, an EM‑31 survey over the area and limitations other than those for salinity risk. considered to be at risk.
108 Salinity management handbook Figure 59. Strategic locations for retaining trees to minimise salinity occurrences or expansion in brigalow landscapes identified as being at risk of salinity.
rainfall between 600 mm and 1 100 mm per annum
Positions on landscape where salting is likely to develop following clearing
clay alluvia softwood scrub, indicator of intake areas (poorly drained, no incised drainage) black tea-tree, indicator of shallow groundwater mudstone • in valley floor main groundwater table (impermeable soils and rock: runoff areas) • on midslope, perched watertable
sandstone brigalow scrub, indicator of saline soils, saline sedimentary rocks (permeable soils and rock: intake areas) and runoff areas
Note, however, that areas that do not currently show evidence of salinity may become saline under changed land use. Voller and Molloy (1993) provide a comprehensive checklist of points to consider when planning clearing operations in south Queensland. Guidelines in addition to those provided in Table 44 include: • Retain a belt of trees at least 100 m wide on the toeslopes all around the catchment to help intercept increased groundwater flows and protect the valley flats from saline outbreaks. • Retain trees along creek lines and geological contacts where permeable horizons overlie impermeable horizons. • Retain trees along roadways and fence lines, scattered over pasture lands or incorporated into soil conservation measures in cropping lands. Stock should be excluded from areas where vegetation has been cleared, at least periodically, to allow regeneration. Strategic locations for retaining trees in landscapes which have been identified as having very high or high risk of salinity are illustrated in Figure 59.
Salinity management handbook 109 Chapter 15 — Engineering methods
Engineering options such as drainage, pumping and • Drainage effluent requires disposal. If the water diversion for managing salinity and taking groundwater is saline, the effluent may be too advantage of excess water include: salty to be released into local waterways (except • intercepting groundwater before it reaches the possibly during times of flood). However, it may discharge area, and possibly using this water, be possible to dilute the effluent with channel depending on quality, for irrigation or stock water for use downstream or in irrigation areas. watering This can be a particularly sensitive issue in some areas where drainage water, in addition to being • draining excess groundwater from discharge saline, may also carry high levels of nutrients and management areas chemicals. • diverting surface water away from discharge management areas When drainage is being designed, future extensions, improvements and the drainage of adjacent areas • evaporating saline water from evaporation basins need to be taken into account. Local extension or ring tanks. officers (specialising in soil conservation or water Initial costs in implementing engineering options resources) offer a comprehensive service for designing may appear high, but these can be balanced against and installing surface and subsurface farm drainage potential losses from reduced land values and lost systems. productivity and income from possible alternative uses of the water. In fact, the costs of implementing Drainage water disposal engineering options such as drainage and pumping, even during the limited period in which other controls Any proposal to dispose of pumped or drained water are being established, can be considerably less than requires a permit from the appropriate authority. the cost of lost productivity. Appropriate permits, licences, easements and so on must be arranged for any effluent disposal, regardless Assistance with aspects of water supply, irrigation of the quality of the water. Outlets must be designed and drainage schemes is available from farm advisory to prevent damage to the receiving watercourse, and services. the disposal of poor quality water must be managed to prevent adverse effects on other lands and water Drainage supplies. Drainage can be an attractive option in situations where recharge areas are not under the control of the Surface drainage landholder with the salinity problem and groundwater Surface drains are used to route floodwaters, quality is good. subsurface drain outflows, irrigation tailwaters and Extensive hydrological investigations may be any other excess surface water away from problem required to determine whether drainage is a viable areas. This may reduce recharge, erosion and option under local conditions and to predict its likely prolonged waterlogging and ponding, as well as effectiveness. When investigating drainage as a providing an opportunity for reusing excess water. salinity management option, these factors need to be considered: Subsurface drainage • Effective drainage requires a height difference Subsurface drainage can be used to prevent between the watertable and the drain outlet. To waterlogging in two ways: drain flat or insufficiently sloping areas, pumps may • Relief drainage is used where there is already a be required, increasing the cost of implementation. high watertable to lower the watertable below the • The hydraulic conductivity of the soil dictates root zone of the crop. drain spacing. To be effective in clay soils, drains • Interception drainage is used to prevent may need to be positioned so close together that waterlogging and high watertables on lower ground this form of management becomes impractical. A by intercepting seepage and transmission of minimum workable spacing for drains is considered groundwater from higher ground. to be about 80 m.
110 Salinity management handbook Figure 60. Installation of subsurface drainage into a salt- Trenches which are located above breaks-of-slope, affected drainage line at Warrill View, Queensland. toeslopes or wetter areas upslope of some subsurface barrier to water movement will act as surface storages, being constantly recharged by the groundwater seepage. Trenches can be pump-tested in a similar manner to bores (refer to Pump site planning page 112). The volume of initial storage needs to be taken into account together with the number of trenches when determining the volume of available water. Water quality and potential uses also need to be considered before trenches are constructed.
Figure 61. Section through a seepage area with a trench showing the change in depth to watertable (Grainger 1995).
trench permeable location seep area
wet surface groundwater flow
Many subsurface drainage systems rely on buried less permeable slotted agricultural pipe or slotted PVC pipe drains with non-slotted pipe taking the water to the discharge point. Clay pipes (tile drains) or rubble drains have also been used, but these are difficult Groundwater pumping to install and maintain. Most types of pipes tend to To determine whether groundwater pumping is a become blocked by plant roots after a period of time. viable option for managing salinity, the following need In suitable soils, mole drains can be used to enhance to be determined: flow into collector drains. Mole drains are created by • the volume of water that needs to be pumped to dragging a ‘plug’ through the soil to create a tunnel for reclaim the affected area water to flow into and along to some type of outfall. • how efficiently this volume can be extracted, The amount and type of clay and the ESP level of the method of extraction and cost soil will determine the stability and useable life of mole drains. The quality of the drainage water will • the quality of the water to be pumped also affect the dispersibility of the soil and thus the • options for using and disposing of water of this stability of the drain. quality, and possible benefits and consequences of its use. The optimal depth for drains depends on soil type and crop. The aim is to maintain the watertable The quantity of water that needs to be pumped to below the root zone of the crop for relief drainage, reclaim a waterlogged or salt-affected discharge and to intercept as much seepage as possible for area can be roughly estimated by calculating interception drainage. a groundwater balance for the catchment (see Catchment groundwater balance estimation page 70). Interception trenches The transmissivity of the aquifer and hydraulic head will determine whether the required volume can be Groundwater interception trenches at right angles to extracted from the aquifer efficiently. the hydraulic gradient (direction of flow) can be used While some information can be inferred from to intercept groundwater (Figure 61). Large trenches surrounding existing bores, water quality and flow rate can provide water storage and can be pumped with can only be accurately determined from a test bore conventional pumping equipment. This engineering in the target interception area. Flow rate will indicate option will only be effective in areas where the which pumping options will be appropriate and groundwater can be accessed fairly close to the economical. surface (1.5 to 5 m depth). This system is being used in the Kingaroy area (Figure 62).
Salinity management handbook 111 Figure 62. A groundwater interception trench in the Figure 63. Air injection to clear a bore hole prior to insertion Kingaroy district, Queensland. of a piezometer tube at Boonah, Queensland.
Depending on the quality of the water, it may be suitable for irrigation (as is or mixed with other Pump site planning water supplies) or for watering stock. (Water quality Preliminary investigations are necessary to determine criteria for irrigation are provided in Irrigation page the best point(s) for groundwater extraction. To 81. Mixing water for irrigation is discussed in the select sites for preliminary investigations, the best following section Marginal quality irrigation waters sources of information are local knowledge, data page 116. Water quality criteria for stock are provided on hydrogeology, and results of previous drilling in in Stock watering page 79.) As noted earlier, any the area. This information will provide a guide to the proposal to dispose of pumped or drained water into likely depth to which bores will have to be sunk, and a watercourse requires a permit from the appropriate thus the likely cost of drilling. Other information that authority. A licence to drill a bore is also required. should be obtained before carrying out preliminary Irrigation quality water from low-flow bores can be investigations includes whether a licence is needed stored in dams for later use. Storage dams need to drill, the type of drill rig most suited to the job, and to be constructed to minimise any leakage to the the means of constructing the bore(s). groundwater. The size of the area to be irrigated will Once a bore has been constructed, a pump test is often be restricted by the available water from the useful for determining the characteristics of the bore(s). A guide to the storage volume required for aquifer at that site. This involves pumping the bore irrigation is given by: for 24 hours and measuring the change in water level A(1500 – r) over time in the bore and the volume of water being S = ...... 33 extracted at regular time intervals. 100 The success of a bore for groundwater extraction where will depend on factors such as the extent of the aquifer, the ability of the aquifer to drain water freely, S is storage volume (ML) the diameter and design of the bore, and pumping A is area to be irrigated (ha) interference from other bores in the vicinity. An r is annual rainfall (mm). analysis of results from preliminary investigations will determine the effect of these factors and provide an indication of the maximum capacity of the bore, optimum pump inlet level, long-term reliability of the bore and stability of the aquifer.
112 Salinity management handbook If the transmissivity of the groundwater aquifer is low, Low to medium flow pumps with a volume throughput multiple bores may need to be installed to obtain of approximately 0.7 to 5 L/s are appropriate for the required quantity of water. Supplying pumps and managing salinity by pumping in the transmission energy sources to each of these bores would quickly area. As multiple bore holes and pumping systems will make such a system uneconomical. One option is to probably be required to intercept a sufficient amount use smaller diameter (and thus less costly) bores and of water, pumps with the energy, maintenance, manifold these together to make a single inlet for a running and cost characteristics of low flow pumps large surface-mounted pump. However, if one bore will be most suitable. breaks suction, the whole system will fail. Because of the limits on suction lift of a surface-mounted pump, Electric and diesel pumps depth to the watertable and distance between the Electric pumping systems can be automated easily bores will be limiting factors in this type of system. for on and off times and extended running periods. A multiple bore system is more likely to have an even However, automated systems are limited to a single drawdown of the groundwater than a single pumped pump rate unless the pulleys are changed to vary bore. As a result, a multiple bore system will provide pump speed. There can be considerable expense better results when the water is being extracted near involved in making electricity available at the bore site to the area affected by the high watertable. if it is not already available. Tariff ratings and possible guarantees of use also need to be considered. Pumps Diesel systems can be easily placed near to bore sites. Fuel storage will limit running times, but the pump In the case of a conventional single bore, pumping rate can be easily changed by varying the governor options include electric submersible pumps, electric setting. or diesel turbines, helical rotor pumps, solar electric pumps, and windmills. Air pumps are particularly Protection equipment for monitoring temperatures suitable for multiple bore systems. and pressures can easily be attached to both electric and diesel systems. Commercially available pumps can be categorised into three types: Sun- and wind-powered pumps • Low flow pumps. Generally intended for stock If the flow is small, solar electric pumps and windmills and domestic water movement, these pumps are can be used economically. If an unused (but working) designed to be very low maintenance and cost windmill is available, pumping with a windmill can almost nothing to run. Solar pumps and windmills be particularly economical. However, some of these are in this category because these pumps do not systems rely on close tolerances for turbines, and need to be located near a conventional power pistons are susceptible to dirty, salty, sandy water; source and can be left unattended for long periods. damage will result if the bore runs dry. The helical Pumping starts and stops automatically, depending rotor pump and some solar diaphragm pumps can on the system’s energy requirements. Some generally handle contaminated water without damage. domestic pumps require conventional power, but these systems are commonly located near a house Solar-powered systems can only operate during where power is available. These systems generally daylight hours unless generated electricity is stored pump up to 1 L/s, although volume throughputs in in a battery. However, it is usually cheaper to store the range 0.7 to 1 L/s generally require larger, more water than electricity. As these systems are electric, expensive systems. it is relatively easy to install automated control and • Low to medium flow pumps. These are generally safety cut-outs. Solar powered systems are relatively fire fighting type pumps for surface pumping portable and have a similar effective lifespan to both applications with a volume throughput of 0.7 to 5 windmills and diesel pumps. L/s. Small turbine and helical rotor pumps in this range are used for some small-scale irrigation, but Air pumps as these pumps can only service a small area, they Another type of pump, not widely used in agriculture, are most economical when used to irrigate high- is the air pump. These pumps can be used to provide value crops. a low-cost dewatering system for regions with low • Medium to high flow pumps. Mostly used for large- yields of 0.5 to 3 L/s. scale irrigation, these are pumps with a volume Air pumps are particularly suitable for multiple bore throughput greater than 5 L/s, and include diesel systems because one compressor can be used to and electrically driven turbine and helical rotor drive a number of bores. This is achieved by installing pumps. As most of the cost of these pumps is in the a network of inexpensive piping between the drive systems and motors, their use under low to compressor and the water extraction points (distances medium flow conditions is generally uneconomical. can be up to several kilometres).
Salinity management handbook 113 There are two basic types of air pumps: Figure 64. Air supply for an air pumping system. • Air injection type. Air injected at the base of a submerged discharge pipe forms a mixture of water and air which is lighter than the head of water at this point, so the aerated water rises to the surface. • Pressure vessel type. A submerged chamber is alternately filled with water and with air; when the chamber is filled with water, a control device (electronic or mechanical) directs compressed air into the chamber, which forces the water into a discharge pipe; when the chamber is empty of water, the compressed air is shut off, the vessel is allowed to refill with water, and the process repeats. The air injection system has no moving parts in contact with water, and the pump foot piece is simple and inexpensive. The control devices used by the pressure vessel type pumps may become unreliable in the long term, and dirty water can reduce the performance of these pumps by inhibiting the action of the non-return valves. With both types, if the bore runs dry, pumping automatically resumes as the bore replenishes. The efficiency of the air injection type is greatest when the head above the pump (that is, the depth to which the pump is submerged below the watertable) is at Figure 65. Above-ground component of a small-scale air least 70% of the total lift required. In other words, injection pumping system. the depth of the pump below the watertable needs to be at least 2.3 times the height difference between the watertable and the outflow point. For example, a pump situated 7 m below the watertable will lift water efficiently to 10 m. (If the watertable is lowered by pumping, the pump will need to be lowered to maintain efficiency.) Thus this system of pumping is most efficient in areas with shallow watertables where the water can be disposed of nearby using flood or furrow irrigation or held in temporary surface water storages.
114 Salinity management handbook Chapter 16 — Irrigation management
Key issues in sustainable irrigation are: Good hydrological information is essential when • preventing excessive salt accumulation in the root planning and developing irrigation areas. When zone gathering and using this information, the following are important: • maintaining soil structural stability • Restrictions to water movement through the • minimising excess drainage of water below the root landscape must be identified and incorporated zone into plans for controlling the watertable (refer to • maintaining crop or plant productivity Landform feature identification page 39). • minimising off-site effects. • Areas with highly permeable soils (which contribute Whether the landholder is considering implementing to high rates of accession to the watertable) must irrigation or adjusting irrigation regimes, the process be identified and considered for specific irrigation of investigating options is basically the same: management or exclusion from the irrigation • Assess the quality of the water currently being used scheme. or proposed for irrigation. Accessions to watertables can be reduced in three • Consider characteristics of the soils in the area ways: proposed for irrigation—in particular, soil structural • For surface water supplies with good quality water stability and permeability. (see Irrigation page 81) on permeable soils, more • Consider characteristics of plant species proposed efficient water management techniques, such as for the irrigated area—in particular, salt tolerance trickle or microsprinkler, can be used to avoid (many species are listed in the appendix Plant salt excess water moving below the root zone. In tolerance data page 124). groundwater-based systems accessing water in an • Determine the likely leaching fraction of the soil unconfined aquifer, this is less of a problem, as and the consequent root zone salinity and amount excess drainage moves to the groundwater where it of drainage below the root zone (which can be becomes available again for irrigation. determined using the computer software package • Under flood or furrow irrigation, surface levelling SALFPREDICT, described in the appendix Useful promotes more uniform soil wetting on clay soils, software packages page 141). so levelled areas can be irrigated for shorter • Estimate the effects of irrigation water sodicity on periods for the same effect. Levelling can improve soil behaviour. surface drainage in flat areas, assisting runoff of excess water from the soil surface. (Procedures for investigating these issues are • Selecting a water application system which is discussed in some detail in Soils page 58 and Waters appropriate for the permeability of the particular page 65.) soil is also important. With permeable soils, Variation in the choice of crop, soil characteristics and sprinkler or trickle irrigation is more satisfactory water quality makes irrigation management decisions than flood irrigation in most cases. With heavy quite complex. The computer package SALFPREDICT cracking clay soils, flood or furrow irrigation, is designed to consider salinity, sodicity and soil and managed to limit tail drain losses, is more efficient plant factors together (discussed in the appendix for wetting the soil. Useful software packages page 141). In surface water schemes, seepage from supply channels can significantly contribute to watertable Irrigation management to rises. To reduce this problem, channels can be lined (often an expensive option), or pipes or fluming can minimise watertable rise be used to distribute the water on-farm. In irrigation areas that are supplied with surface water, Subsoil drainage or watertable pumping and water efficient water management is essential to prevent reuse can be used to control high watertables. watertable rise. Because some leaching below the However, several factors need to be considered root zone is inevitable, monitoring of water levels is an regarding drainage, such as whether there is an essential aspect of irrigation management. adequate height difference between the watertable
Salinity management handbook 115 and the drain outlet, soil hydraulic conductivity • Allow salt to accumulate during the growing and its implications for drain spacing, options for season and then implement specific leaching disposing of drain effluent, water quality, and aquifer irrigations (that is, apply extra water during transmissivity. (Refer to Engineering methods page 110 periodic preplanned irrigations). Water use is for a discussion of these issues.) more efficient, but some yield loss may result from salt accumulation. In all soils other than slowly permeable soils, leaching in small amounts is Marginal quality irrigation more efficient than ponding. In slowly permeable waters soils, ponding is more efficient. Timing of leaching irrigations depends on crop salt tolerance and The best approach is to match soils, irrigation waters water salinity. For annual crops, pre- or post-crop and crops to minimise negative impacts of irrigation irrigation is preferred. Pre-cropping irrigation on soils. In order to implement this, it is necessary will assist germination by leaching surface salt. to have an accurate assessment of water quality. Cropping in cooler months or, alternatively, (Assessing water quality is covered in Irrigation page irrigating to coincide with a period of major 81.) seasonal rainfall will contribute to greater leaching. Where it is not possible to match all these factors, For perennial crops, leaching irrigations during a number of irrigation management practices can dormant periods are more effective, since less be used to minimise the effects of marginal quality evapotranspiration occurs. irrigation water on soils and crops. These practices With slowly permeable soils, the use of marginal include changing the frequency, duration and method quality water for leaching may contribute to higher of irrigation, judicious timing of leaching irrigations, soil salinity levels, because more salt can be added to mixing irrigation water supplies, and cultural practices the soil than is removed during leaching even though including soil amendments. These are outlined below there is an increase in the leaching due to flocculation and described in detail by Ayers and Westcot (1976). by the salts. In this situation, seasonal rainfall will Shaw et al. (1987) describe the limitations of several provide leaching. In dry years, salinity effects on irrigation management approaches in practice. plants will be more severe. Salinity and sodicity are the two major issues with marginal quality water use. Management practices to Choose the best irrigation method for the minimise the effects of such waters are outlined in the conditions following sections. The method of irrigation used can affect salt accumulation. Saline water • Flood irrigation provides an even application of water but can be wasteful, particularly in a high- Irrigate more frequently frequency irrigation scheme. In cracking clay soils, Provided the root zone is wet, more frequent flood irrigation provides good recharge of soil irrigation reduces plant water stress, dilutes the soil water and some potential for leaching if the soil is solution, and sometimes increases leaching of salts. cracked before irrigation. Increasing irrigation frequency is appropriate where • Furrow irrigation contributes to salt accumulation irrigation water is available on demand and soils are in adjacent rows through capillary rise and permeable. However, the cost of irrigation may also be evaporation from the highest parts of the ridges. increased, as may be the likelihood of watertable rise. Thus planting in the furrow or on the side of larger hills will reduce salt concentration. (See Mounding Use extra water to control salinity by leaching page 101.) Two options are available here: • Sprinkle irrigation provides good control and • In soils with good drainage and where the maximum flexibility. However, it can cause leaf watertable is not high, maintain salt balance damage (burn) and salt precipitation on leaves. throughout the season by applying extra water each Some water is lost through evaporation, which irrigation for leaching. increases the salinity of water on the leaves. Both leaf damage and evaporation can be reduced by sprinkling at night. Precipitates on leaves can be reduced by increasing the sprinkler rotation speed. In cracking clay soils, the lower application rate of sprinkle irrigation can cause surface sealing and greatly reduce soil wetting.
116 Salinity management handbook • Trickle irrigation is efficient but contributes to salt Table 45. Relative tolerance of sprinkled crops to salinity accumulation in the soil surface and at the edge of impinging on the leaves or roots. Salinity levels are wetted areas. Under rainfall, salts accumulated at expressed as the electrical conductivity of the irrigation water (EC ) (after Maas 1985). Table used with kind the soil surface can be leached down into the root iw permission of E. V. Maas and Kluwer Academic Publishers zone in sufficient concentrations to kill vegetation. (Plant and Soil, 89, pp. 273–84, ‘Crop tolerance to saline These effects can be reduced by applying a sprinkling water’). surface mulch to minimise evaporation or by burying the emitter at some depth in the root zone. Salinity threshold Microsprinklers are an alternative option. Common Scientific name 1 2 name Max. ECiw Max. ECiw Some species can tolerate higher salinity levels in (dS/m) (dS/m) the soil than in water which is applied to the leaves. Grain crops This is specifically relevant to crops under irrigation. Barley Hordeum vulgare 1.0–2.0 5.3 Methods for managing this situation and being able Corn Zea mays 1.0–2.0 1.1 to continue to irrigate crops with marginally saline waters (in relation to each crop species) include Cotton Gossypium 3.0–6.0 5.1 Safflower Carthamus irrigating below the leaves and irrigating at night (to 1.0–2.0 reduce salt on the leaves left by rapid evaporation tinctorius during the day). Some crops for which information is Sesame Sesamum indicum 1.0–2.0 available are listed in Table 45. Sorghum Sorghum bicolor 1.02–2.0 4.5 Sunflower Helianthus annuus 14–16 Mix water supplies sp. Mixing water supplies can reduce salinity hazard Fruit if good quality water is available in addition to the Almond Prunus dulcis < 0.5 1.0 marginal quality water. However, mixing a saline water Apricot Prunus armeniaca < 0.5 1.1 with good quality water is not necessarily a good Citrus Citrus sp. < 0.5 1.1 strategy. If the saline water is of higher salinity than the plant can tolerate, diluting it with a less saline Grape Vitis sp. 0.5–1.0 1.0 water is a waste because once the threshold salinity is Plum Prunus domestica <0.5 1.0 reached, the plant cannot use the water. Strawberry Fragaria 2.0–4.0 0.7 Two options are preferred for using good and marginal Heavy vegetables quality water supplies for irrigation: Potato Solanum 0.5–1.0 1.1 tuberosum • Alternate applications of marginal quality water with applications of good quality water, when Sugarbeet Beta vulgaris 3.0–6.0 4.7 available. This will maintain a lower salt balance, Pasture provided sodicity is not a problem. With species Lucerne Medicago sativa 1.0–2.0 1.3 that have differing levels of salinity tolerance Vegetables depending on stage of growth, water quality can be Cauliflower Brassica oleracea 3.0–6.0 matched to stage of growth. Cucumber Cucumis sativus 1.0–2.0 1.7 • Alternate salt-tolerant and salt-sensitive crops with Pepper Capsicum annum 0.5–1.0 1.0 different irrigation waters. This option is preferred Tomato Lycopersicon where good quality water is available and seasonal 0.5–1.0 1.7 lycopersicum rainfall promotes leaching.
Notes 1. Saline waters (primarily NaCl) with EC values higher than the Sodic water iw threshold are expected to cause foliar injury on crops sprinkled five Sodic irrigation waters generally result in soil or more hours each week during the irrigation season. The degree of dispersion with consequent soil surface sealing, injury is influenced by the cultural and environmental conditions. crusting, erosion, poor water entry and poor 2. Salinity exceeding the threshold is expected to decrease the yield seedbeds. This dispersion is reduced by the salinity below that of crops irrigated with non-saline water. The relationship, level in an irrigation water but problems develop ECse = 1.5 ECiw, was used to express the soil salinity threshold in under heavy rainfall when salts are leached from the terms of ECiw, that is, a leaching fraction of 0.15. soil surface. Points listed above under irrigating with marginally saline waters are generally relevant to irrigating with marginally sodic waters, in addition to the following points.
Salinity management handbook 117 Mix water supplies Irrigate for longer periods of time Mixing available waters to maintain a satisfactory A longer duration of irrigation is required with sodic sodicity level can be a viable management option, waters since sodic soils have lower infiltration rates providing salinity levels are satisfactory. and need more time for the water to become wet. Irrigation across slope or recycling taildrain water will Apply gypsum help conserve water. Long irrigations, however, can Gypsum (calcium sulfate) can be used as a soil lead to aeration problems. amendment to improve the structure of surface soils and to alleviate some of the adverse effects Choose the best irrigation method for the of high sodicity waters and those with residual conditions alkali (Na2CO3). Gypsum improves soil structure Spray irrigation can cause surface crusting and sealing by increasing flocculation of clay particles through on sodic soils if used during crop establishment increased electrolyte concentration and by exchange without a surface mulch to protect the soil surface. of calcium for sodium on the exchange complex. Capillary wetting of hills from furrow irrigation This results in better surface soil aggregation and results in less soil slaking and dispersion than spray consequently reduced waterlogging and crusting and irrigation. can improve surface soil drainage. Long-term benefits of gypsum in exchanging for sodium can only occur Protect the soil surface if the exchanged sodium can be leached out of the Medium seedbeds are preferable to fine seedbeds profile. Thus on soils with slowly permeable subsoils to reduce slaking and dispersion and crusting on there will be limited benefits. irrigation. Adding large quantities of organic matter Gypsum has a relatively low solubility; it is estimated will help maintain soil structure of some soils and that no more than 700 kg of surface-applied pure reduce cloddiness. gypsum can be dissolved per megalitre of irrigation water in any one year (Ayers & Westcot 1976)—that Reclaim sodic soils using saline water is, 100 mm depth of water per hectare. Thus under If the land value is very high and there are advantages common conditions (assuming rainfall of 800 mm/ in reducing the soil sodicity levels, a reclamation yr and irrigation water application of 500–600 mm/ method for sodic soils with very low permeability yr), an application of around 1 t/ha/yr of pure gypsum can be attempted. Using this method, high salt could be dissolved. Because of impurities in gypsum, concentration waters are applied initially to flocculate unevenness of distribution and loss from surface the soil. Once the permeability is raised, the SAR runoff, the general recommendation is 2–6 t/ha of the water is gradually reduced as the salinity is every year or per two-year period. In some situations, reduced, resulting in low ESP and improved soil depending on the gypsum responsiveness of a soil, structure. This process needs to be monitored closely. applications of 5 t/ha seem to be more successful in achieving a measurable effect. Gypsum added directly to irrigation water is much more effective than when applied to the soil surface, but the cost of dissolution will increase the overall cost. The above recommendations depend on soil chemistry. The solubility of gypsum varies with different ions (discussed in Basic chemical processes and solubility of salts page 74). Thus in some salt- affected soils the solubility of gypsum may be increased, particularly if NaCl is present. (Some helpful notes on gypsum application rates and conversions are provided in Notes on gypsum page 160.)
Apply other soil amendments Sulfur application can be useful on sodic soils if there is a high level of calcium carbonate at the soil depth required. Also, sulfuric acid can be used for high alkalinity and residual alkali waters. However, sulfuric acid is not appropriate if calcium or magnesium levels are low since sodicity will remain high. Handling this acid is dangerous.
118 Salinity management handbook Appendixes
1 Landscape features diagnostic chart 2 Plant salt-tolerance data 3 Pasture species for saline soils 4 Tree species for salinity management 5 Useful software packages 6 Salinity publications for further reference
Appendixes 119 Landscape features diagnostic chart
Basalt form Figure 66. Salting at the contact between basalt and underlying sediments near Kingaroy, Queensland. Both seepage and watertable salting can occur where basalt overlies less permeable rock, where regions of variable permeability occur within the basalt, or where the basalt is in contact with adjacent formations.
R restriction seepage R water flow
basalt
sandstone/mudstone
Alluvial fan Figure 67. Expression of salt in a catena sequence upslope of a flat alluvial area near Muttapilly, Queensland. Discharge areas can occur where subsurface water encounters deep clays or more recent alluvia.
R
recent alluvium
basement rock old alluvium
Catena form Discharge areas can occur in the lower slope or at break-of-slope positions where soils or geologic features restrict water movement. Lower slope soils may be sodium- and salt-affected.
R
basement rock
120 Appendixes — Landscape features diagnostic chart Catchment restriction—natural Figure 68. Salting on the floodplain of the Todd River upslope of the hydrologic restriction by the Macdonnell Salting can occur upslope of natural or artificial Ranges at Alice Springs, Northern Territory. restrictions that narrow the width or depth of the catchment throat.
R
Catchment restriction—artificial Salting can occur upslope of roads or stock routes that have compacted the soil. R R road
basement rock
Figure 69. Bare drainage line due to salinisation in a catchment near Kingaroy, Queensland. Alluvial valley Salting can occur where the valley is very flat and the hydraulic gradient is very low. R
alluvium
basement rock
Appendixes — Landscape features diagnostic chart 121 Stratigraphic form Figure 70. Hillslope saline seepage on the Darling Downs, Queensland. Small seepages and salted areas can appear on hillslopes where water flow encounters layers of rock with reduced permeability.
R R R
Confluence of streams Watertables can rise where streams join and deposits of fine sediments with low lateral permeability restrict groundwater flow.
R R Figure 71. Linear pattern of salting as a result of geologic dykes below a leaking farm dam in the Lower Burdekin, R Queensland.
Dykes Incipient or permanent salting can develop where water movement downslope encounters less permeable dykes across the direction of the slope.
R
122 Appendixes — Landscape features diagnostic chart Dams Figure 72. Salting upstream of a small farm dam due to the dam acting as a hydraulic barrier near Wellington, New Salting can occur upstream of any dam or downstream South Wales. of a leaking dam where a less permeable subsoil layer underlies the leak. R
pond bank
leakage
watertable level rising
Lakes Salt can accumulate where surface flushing is limited and the lake acts as a surface or groundwater terminus. swamp or lake that may become saline
Figure 73. Salted area from the top of an ancient mound spring associated with faulting in South Australia.
Geologic faulting Incipient or permanent salting can develop where water movement downslope encounters faults. Faults can also provide a preferential flow path for the water to the surface, resulting in springs.
R
Appendixes — Landscape features diagnostic chart 123 Plant salt-tolerance data
The following tables (Tables 46 and 47) list salt- be considered in the light of local conditions and tolerance data for crop, pasture, vegetable, fruit and plant/variety differences. ornamental species compiled from the work of a • Rainfall amount and timing will have an impact. number of researchers. The data source is indicated in Adverse osmotic adjustment has been noted for the final column of the table. soybeans. 1. Maas & Hoffman (1977) The threshold values for 90%, 75% and 50% yields 2. Ayers & Westcot (1976) have been calculated from the data on salinity 3. Russell (1976) threshold and productivity decrease with increasing 4. Maas (1986) salinity in excess of the threshold. To determine the actual yield response of a plant species, the following 5. West & Francois (1982) relationship between the salinity threshold and the 6. Bresler, McNeal & Carter (1982) percentage productivity decrease per dS/m increase 7. Ayers (1977) above this threshold value is used 8. Heuer, Meiri & Shalhevet (1986) (from Maas & Hoffman 1977): 9. Shaw et al. (1987)
Yr = 100 – B(ECse – A) ...... 34 Note: The data from reference 3 (Russell 1976) have been recalculated according to the method of Maas & Hoffman (1977), using a number of assumptions which may affect their accuracy. where However, these data are included because Russell provides local Queensland data. Yr is relative yield
ECse is theoretical value of root zone ECse The table is provided twice for ease of access. In resulting in relative yield Yr Table 46 the information is presented in alphabetical B is percent productivity decrease per order by common name, divided into categories of dS/m increase above the threshold grain, fruit, heavy vegetables, ornamental, pasture value (from Table 46) and vegetables. In Table 47 the information is listed in order of sensitivity at 90% yield (or at the end of A is salinity threshold value of root zone EC (from Table 46). the table by salinity threshold if productivity decrease se data are not available). Rearranging this equation to find the ECse associated When using these tables to investigate the likely with a particular yield gives: effects of salinity on yield, the following points need 100 – Y to be considered: EC = A + r ...... 35 se B • The data are not absolute and vary with the method of assessment, climate and cultural practices. To calculate an ECse, for instance, which will result • The salt tolerance ratings in this table have been in approximately 90% yield (Yr = 90), this equation largely evaluated from experiments where the becomes: salinity was imposed after seedling establishment and thus do not necessarily apply to germination 100 – 90 EC and early seedling establishment. se(90%) = A + ...... 36 B • The data assume that the soil is uniformly saline, which does not accurately reflect field conditions. Similarly, the equation for calculating ECse for • The data assume that the dominant anion is approximately 75% yield is: chloride, so the chemical composition of salts 100 – 75 may affect how applicable this information is in a EC = A + ...... 37 particular field situation. se(75%) B • In one or two places, two sets of data have been provided for one species. This has occurred where These equations, which have been used to generate the different researchers have established differing relative yield figures in the following tables, can also values, providing emphasis that the data must be used to calculate relative yield from threshold and productivity decrease data for species not listed here.
124 Appendixes — Plant salt-tolerance data Table 46. Plant salt-tolerance data, in alphabetical order by common name, within broad plant groups.
Soil salinity EC at Productivity se Salinity decrease Common name Scientific name threshold 90% 75% 50% Reference per dS/m (EC ) yield yield yield se increase (%)
Grains Barley, grain Hordeum vulgare 8.0 5.0 10.0 13.0 18.0 1 Corn, grain, sweet Zea mays 1.7 12.0 2.5 3.8 5.9 1 Cotton Gossypium hirsutum 7.7 5.2 9.6 12.5 17.3 1 Cowpea (seed) Vigna unguiculata 1.6 9.0 2.7 4.4 7.2 9 Cowpea, Caloona Vigna unguiculata var. Caloona 2.0 10.8 2.9 4.3 6.6 3 Flax/Linseed Linum usitatissimum 1.7 12.0 2.5 3.8 5.9 1 Oats Avena sativa 5.0 20.0 5.5 6.3 7.5 9 Peanut Arachis hypogaea 3.2 29.4 3.5 4.1 4.9 2 Phasey bean, Macroptilium lathyroides 0.8 7.9 2.1 4.0 7.1 3 Murray Rice, paddy Oryza sativa 3.0 12.2 3.8 5.1 7.1 1 Safflower Carthamus tinctorius 6.5 6 Sorghum Sorghum bicolor 6.8 15.9 7.4 8.4 9.9 4 Sorghum, crooble Sorghum almum 8.3 11.2 9.2 10.5 12.8 3 Soybean Glycine max 5.0 20.0 5.5 6.3 7.5 1 Sugarcane Saccharum officinarum 1.7 5.9 3.4 5.9 10.2 1 Sunflower Helianthus annuus spp. 5.5 25.0 5.9 6.5 7.5 9 Wheat Triticum aestivum 6.0 7.1 7.4 9.5 13.0 1 Wheat, durum Triticum turgidum 5.7 5.4 7.6 10.3 15.0 4 Fruits Almond Prunus dulcis 1.5 18.0 2.1 2.9 4.3 1 Apple Malus sylvestris 1.0 18.0 1.6 2.4 3.8 1 Apricot Prunus armeniaca 1.6 23.0 2.0 2.7 3.8 1 Avocado Persea americana 1.3 21.0 1.8 2.5 3.7 7 Blackberry Rubus spp. 1.5 22.2 2.0 2.6 3.8 1 Boysenberry Rubus ursinus 1.5 22.2 2.0 2.6 3.8 1 Date Phoenix dactylifera 4.0 3.4 6.9 11.4 18.7 1 Fig Ficus carica 4.2 6 Grape Vitis spp. 1.5 9.5 2.6 4.1 6.8 1 Grapefruit Citrus paradisi 1.8 16.1 2.4 3.4 4.9 1 Guava, pineapple Feijoa sellowiana 1.2 6 Lemon Citrus limon 1.0 6 Natal plum Carissa macrocarpa 6.0 6 Olive Olea europaea 4.0 6 Orange Citrus sinensis 1.7 15.9 2.3 3.3 4.8 1 Peach Prunus persica 3.2 18.8 3.7 4.5 5.9 1 Pear Pyrus spp. 1.0 6 Plum Prunus domestica 1.5 18.2 2.0 2.9 4.2 1 Prune Prunus domestica 1.0 6 Pomegranate Punica granatum 4.0 6 Raspberry Rubus idaeus 1.0 6
Appendixes — Plant salt-tolerance data 125 Soil salinity EC at Productivity se Salinity decrease Common name Scientific name threshold 90% 75% 50% Reference per dS/m (EC ) yield yield yield se increase (%)
Rockmelon Cucumis melo 2.2 7.3 3.6 5.6 9.0 7 Strawberry Fragaria 1.0 33.3 1.3 1.8 2.5 1 Heavy vegetables Beet, garden Beta vulgaris 4.0 9.0 5.1 6.8 9.6 1 Beet, sugar Beta vulgaris 7.0 5.9 8.7 11.2 15.5 1 Onion Allium cepa 1.2 16.1 1.8 2.8 4.3 1 Potato Solanum tuberosum 1.7 12.0 2.5 3.8 5.9 1 Sweet potato Ipomoea batatas 1.5 11.1 2.4 3.8 6.0 1 Ornamentals Arbor-vitae Thuja orientalus 2.0 6 Algerian ivy Hedera canariensis 1.0 6 Bambatsi Panicum coloratum 1.5 3.2 4.6 9.3 17.1 3 Bottlebrush Callistemon viminalis 1.5 6 Bougainvillea Bougainvillea spectabilis 8.5 6 Buxus microphylla var. Boxwood 1.7 10.8 2.6 4.0 6.3 1 Japonica Chinese holly Ilex cornuta 1.0 6 Dracaena Dracaena endivisa 4.0 9.1 5.1 6.7 9.5 1 Euonymus japonica var. Euonymus 7.0 6 grandiflora Heavenly bamboo Nandina domestica 1.0 6 Hibiscus rosa-sinensis cv. Hibiscus 1.0 6 Brilliante Juniper Juniperus chinensis 1.5 9.5 2.6 4.1 6.8 1 Lantana Lantana camara 1.8 1 Oleander Nerium oleander 2.0 21.0 2.5 3.2 4.4 1 Pittosporum Pittosporum tobira 1.0 6 Privet Ligustrum lucidum 2.0 9.1 3.1 4.7 7.5 1 Pyracantha Pyracantha braperi 2.0 9.1 3.1 4.7 7.5 1 Rose Rosa spp. 1.0 6 Star jasmine Trachelospermum jasminoides 1.6 6 Viburnum Viburnum spp. 1.4 13.2 2.2 3.3 5.2 1 Xylosma Xylosma senticosa 1.5 13.3 2.3 3.4 5.3 1 Pastures Barley, forage Hordeum vulgare 6.0 7.0 7.4 9.6 13.1 1 Barley, hay Hordeum vulgare 6.0 7.1 7.4 9.5 13.0 2 Barrel medic, Medicago truncatula 3.0 14.6 3.7 4.7 6.4 3 Cyprus Barrel medic, Medicago truncatula 1.0 7.7 2.3 4.2 7.5 3 Jemalong Buffel grass, Cenchrus ciliaris var. Gayndah 5.5 10.3 6.5 7.9 10.4 3 Gayndah Buffel grass, Cenchrus ciliaris var. Nunbank 6.0 6.8 7.5 9.7 13.4 3 Nunbank
126 Appendixes — Plant salt-tolerance data Soil salinity EC at Productivity se Salinity decrease Common name Scientific name threshold 90% 75% 50% Reference per dS/m (EC ) yield yield yield se increase (%)
Clover, alsike, Trifolium spp. 1.5 12.0 2.3 3.6 5.7 1 ladino, red Clover, berseem Trifolium alexandrinum 2.0 10.3 3.0 4.4 6.9 3 Clover, berseem Trifolium alexandrinum 1.5 5.8 3.2 5.8 10.1 1 (USA) Clover, rose Trifolium hirtum 1.0 8.9 2.1 3.8 6.6 3 (Kondinin) Clover, strawberry Trifolium fragiferum 1.6 10.3 2.6 4.0 6.5 3 (Palestine) Clover, white (New Trifolium repens 1.0 9.6 2.0 3.6 6.2 3 Zealand) Clover, white Trifolium semipilosum 1.5 12.1 2.3 3.6 5.6 3 (Safari) Corn, forage Zea mays 1.8 7.4 3.2 5.2 8.6 1 Couch grass Cynodon dactylon 6.9 6.4 8.5 10.8 14.7 1 Cowpea Vigna unguiculata 1.3 14.3 2.0 3.0 4.8 1 (vegetative) Desmodium, green Desmodium intortum 2.1 14.9 2.8 3.8 5.5 3 leaf Desmodium, Desmodium uncinatum 1.0 22.7 1.4 2.1 3.2 3 silverleaf Dodonea Dodonea viscosa 1.0 7.8 2.3 4.2 7.4 1 Dolichos Rongai Lablab purpureus 1.0 15.6 1.6 2.6 4.2 3 Fescue Festuca elatior 3.9 5.3 5.8 8.6 13.3 1 Glycine tinaroo Glycine wightii 1.8 9.9 2.8 4.3 6.9 3 Green panic, Petri Panicum maximum 3.0 6.9 4.4 6.6 10.2 3 Kikuku grass, Pennisetum clandestinum 3.0 3.0 6.3 11.3 19.7 3 Whittet Leichhardt Macrotyloma uniflorum 3.0 15.6 3.6 4.6 6.2 3 Lotononis, Miles Lotononis bainesii 1.0 12.2 1.8 3.1 5.1 3 Lovegrass Eragrostis spp. 2.0 8.5 3.2 4.9 7.9 1 Lucerne, Hunter Medicago sativa 2.0 6.0 3.7 6.2 10.3 3 River Lucerne, Hunter Medicago sativa 1.5 6.9 2.9 5.1 8.7 3 River (temperate) Lucerne (USA) Medicago sativa 2.0 7.3 3.4 5.4 8.8 1 Meadow foxtail Alopecurus pratensis 1.5 9.7 2.5 4.1 6.7 1 Orchard grass Dactylis glomerata 1.5 6.2 3.1 5.5 9.6 1 Pangola grass Digitaria decumbens (pentzii) 2.0 4.0 4.5 8.3 14.5 3 Paspalum Paspalum dilatatum 1.8 9.0 2.9 4.6 7.4 3 Phalaris Phalaris tuberosa (aquatica) 4.2 6 Rhodes grass, Chloris gayana 7.0 3.2 10.1 14.8 22.6 3 Pioneer Sesbania Sesbania exaltata 2.3 7.0 3.7 5.9 9.4 1 Setaria, Nandi Setaria sphacelata var. sericea 2.4 12.2 3.2 4.5 6.5 3 Siratro Macroptilium atropurpureum 2.0 7.9 3.3 5.2 8.3 3 Snail medic Medicago scutellata 1.5 12.9 2.3 3.4 5.4 3
Appendixes — Plant salt-tolerance data 127 Soil salinity EC at Productivity se Salinity decrease Common name Scientific name threshold 90% 75% 50% Reference per dS/m (EC ) yield yield yield se increase (%)
Strand medic Medicago littoralis 1.5 11.6 2.4 3.7 5.8 3 Sudan grass Sorghum sudanense 2.8 4.3 5.1 8.6 14.4 1 Townsville stylo Stylosanthes humilis 2.4 20.4 2.9 3.6 4.9 3 Trefoil, big Lotus uliginosus 3.0 11.1 3.9 5.3 7.5 1 Trefoil, birdsfoot Lotus corniculatus 5.0 10.0 6.0 7.5 10.0 1 Urochloa Urochloa mosambicensis 8.5 12.4 9.3 10.5 12.5 3 Wheatgrass, Agropyron desertorum 3.5 4.0 6.0 9.8 16.0 1 crested Wheatgrass, Agropyron cristatum 7.5 6.9 8.9 11.1 14.7 1 fairway Wheatgrass, tall Agropyron elongatum 7.5 4.2 9.9 13.5 19.4 1 Vegetables Bean Phaseolus vulgaris 1.0 18.9 1.5 2.3 3.6 1 Broadbean Vicia faba 1.6 9.6 2.6 4.2 6.8 1 Broccoli Brassica oleracea 2.8 9.1 3.9 5.5 8.3 1 Cabbage Brassica oleracea var. Capitata 1.8 9.7 2.8 4.4 7.0 1 Carrot Daucus carota 1.0 14.1 1.7 2.8 4.5 1 Cauliflower Brassica oleracea 2.5 6 Celery Apium graveolens 1.8 6.2 3.4 5.8 9.9 4 Cucumber Cucumis sativus 2.5 13.0 3.3 4.4 6.3 1 Eggplant Solanum melongena 1.1 6.9 2.5 4.7 8.3 8 Kale Brassica campestris 6.5 6 Lettuce Latuca sativa 1.3 13.0 2.1 3.2 5.1 1 Pea Pisum sativum L. 2.5 6 Pepper Capsicum annum 1.5 14.1 2.2 3.3 5.0 9 Rosemary Rosmarinus lockwoodii 4.5 6 Spinach Spinacia oleracea 2.0 7.6 3.3 5.3 8.6 1 Squash Cucurbita maxima 2.5 6 Squash, scallop Cucurbita pepo melopepo 3.2 16.0 3.8 4.8 6.3 4 Tomato Lycopersicon esculentum 2.3 18.9 2.8 3.6 4.9 1 Turnip Brassica rapa 0.9 9.0 2.0 3.7 6.5 4 Zucchini Cucurbita pepo melopepo 4.7 9.4 5.8 7.4 10.0 4
128 Appendixes — Plant salt-tolerance data Table 47. Plant salt-tolerance data, in numerical order by sensitivity at 90% yield (or at the end of the table by salinity threshold if productivity decreases data not available). (* indices data not available.)
Soil salinity EC at Productivity se Salinity decrease Common name Scientific name threshold 90% 75% 50% Reference per dS/m EC yield yield yield se increase (%)
Strawberry Fragaria 1.0 33.3 1.3 1.8 2.5 1 Desmodium, Desmodium uncinatum 1.0 22.7 1.4 2.1 3.2 3 silverleaf Bean Phaseolus vulgaris 1.0 18.9 1.5 2.3 3.6 1 Apple Malus sylvestris 1.0 18.0 1.6 2.4 3.8 1 Dolichos Rongai Lablab purpureus 1.0 15.6 1.6 2.6 4.2 3 Carrot Daucus carota 1.0 14.1 1.7 2.8 4.5 1 Lotononis, Miles Lotononis bainesii 1.0 12.2 1.8 3.1 5.1 3 Onion Allium cepa 1.2 16.1 1.8 2.8 4.3 1 Avocado Persea americana 1.3 21.0 1.8 2.5 3.7 7 Turnip Brassica rapa 0.9 9.0 2.0 3.7 6.5 4 Clover, white (New Trifolium repens 1.0 9.6 2.0 3.6 6.2 3 Zealand) Cowpea Vigna unguiculata 1.3 14.3 2.0 3.0 4.8 1 (vegetative) Blackberry Rubus spp. 1.5 22.2 2.0 2.6 3.8 1 Boysenberry Rubus ursinus 1.5 22.2 2.0 2.6 3.8 1 Plum Prunus domestica 1.5 18.2 2.0 2.9 4.2 1 Apricot Prunus armeniaca 1.6 23.0 2.0 2.7 3.8 1 Phasey bean, Macroptilium lathyroides 0.8 7.9 2.1 4.0 7.1 3 Murray Clover, rose Trifolium hirtum 1.0 8.9 2.1 3.8 6.6 3 (Kondinin) Lettuce Latuca sativa 1.3 13.0 2.1 3.2 5.1 1 Almond Prunus dulcis 1.5 18.0 2.1 2.9 4.3 1 Viburnum Viburnum spp. 1.4 13.2 2.2 3.3 5.2 1 Pepper Capsicum annum 1.5 14.1 2.2 3.3 5.0 9 Barrel medic, Medicago truncatula 1.0 7.7 2.3 4.2 7.5 3 Jemalong Dodonea Dodonea viscosa 1.0 7.8 2.3 4.2 7.4 1 Clover, white Trifolium semipilosum 1.5 12.1 2.3 3.6 5.6 3 (Safari) Clover, alsike, Trifolium spp. 1.5 12.0 2.3 3.6 5.7 1 ladino, red Snail medic Medicago scutellata 1.5 12.9 2.3 3.4 5.4 3 Xylosma Xylosma senticosa 1.5 13.3 2.3 3.4 5.3 1 Orange Citrus sinensis 1.7 15.9 2.3 3.3 4.8 1 Strand medic Medicago littoralis 1.5 11.6 2.4 3.7 5.8 3 Sweet potato Ipomoea batatas 1.5 11.0 2.4 3.8 6.0 7 Grapefruit Citrus paradisi 1.8 16.1 2.4 3.4 4.9 1 Eggplant Solanum melongena 1.1 6.9 2.5 4.7 8.3 8 Meadow foxtail Alopecurus pratensis 1.5 9.7 2.5 4.1 6.7 1 Corn, grain, sweet Zea mays 1.7 12.0 2.5 3.8 5.9 1 Flax/Linseed Linum usitatissimum 1.7 12.0 2.5 3.8 5.9 1
Appendixes — Plant salt-tolerance data 129 Soil salinity EC at Productivity se Salinity decrease Common name Scientific name threshold 90% 75% 50% Reference per dS/m EC yield yield yield se increase (%)
Potato Solanum tuberosum 1.7 12.0 2.5 3.8 5.9 1 Oleander Nerium oleander 2.0 21.0 2.5 3.2 4.4 1 Grape Vitis spp. 1.5 9.5 2.6 4.1 6.8 1 Juniper Juniperus chinensis 1.5 9.5 2.6 4.1 6.8 1 Broadbean Vicia faba 1.6 9.6 2.6 4.2 6.8 1 Clover, strawberry Trifolium fragiferum 1.6 10.3 2.6 4.0 6.5 3 (Palestine) Buxus microphylla var. Boxwood 1.7 10.8 2.6 4.0 6.3 1 Japonica Cowpea (seed) Vigna unguiculata 1.6 9.0 2.7 4.4 7.2 9 Cabbage Brassica oleracea var. Capitata 1.8 9.7 2.8 4.4 7.0 1 Glycine tinaroo Glycine wightii 1.8 9.9 2.8 4.3 6.9 3 Desmodium, green Desmodium intortum 2.1 14.9 2.8 3.8 5.5 3 leaf Tomato Lycopersicon esculentum 2.3 18.9 2.8 3.6 4.9 1 Paspalum Paspalum dilatatum 1.8 9.0 2.9 4.6 7.4 3 Vigna unguiculata var. Cowpea, Caloona 2.0 10.8 2.9 4.3 6.6 3 Caloona Townsville stylo Stylosanthes humilis 2.4 20.4 2.9 3.6 4.9 3 Lucerne, Hunter Medicago sativa 1.5 6.9 2.9 5.1 8.7 3 River (temperate) Clover, berseem Trifolium alexandrinum 2.0 10.3 3.0 4.4 6.9 3 Orchard grass Dactylis glomerata 1.5 6.2 3.1 5.5 9.6 1 Privet Ligustrum lucidum 2.0 9.1 3.1 4.7 7.5 1 Pyracantha Pyracantha braperi 2.0 9.1 3.1 4.7 7.5 1 Clover, berseem Trifolium alexandrinum 1.5 5.8 3.2 5.8 10.1 1 (USA) Corn, forage Zea mays 1.8 7.4 3.2 5.2 8.6 1 Lovegrass Eragrostis spp. 2.0 8.5 3.2 4.9 7.9 1 Setaria, Nandi Setaria sphacelata var. sericea 2.4 12.2 3.2 4.5 6.5 3 Siratro Macroptilium atropurpureum 2.0 7.9 3.3 5.2 8.3 3 Spinach Spinacia oleracea 2.0 7.6 3.3 5.3 8.6 1 Cucumber Cucumis sativus 2.5 13.0 3.3 4.4 6.3 1 Sugarcane Saccharum officinarum 1.7 5.9 3.4 5.9 10.2 1 Celery Apium graveolens 1.8 6.2 3.4 5.8 9.9 4 Lucerne (USA) Medicago sativa 2.0 7.3 3.4 5.4 8.8 1 Peanut Arachis hypogaea 3.2 29.4 3.5 4.1 4.9 2 Rockmelon Cucumis melo 2.2 7.3 3.6 5.6 9.0 7 Leichhardt Macrotyloma uniflorum 3.0 15.6 3.6 4.6 6.2 3 Lucerne, Hunter Medicago sativa 2.0 6.0 3.7 6.2 10.3 3 River Sesbania Sesbania exaltata 2.3 7.0 3.7 5.9 9.4 1 Barrel medic, Medicago truncatula 3.0 14.6 3.7 4.7 6.4 3 Cyprus Peach Prunus persica 3.2 18.8 3.7 4.5 5.9 1 Rice, paddy Oryza sativa 3.0 12.2 3.8 5.1 7.1 1 Squash, scallop Cucurbita pepo melopepo 4.8 6.3 3.2 16.0 3.8 4
130 Appendixes — Plant salt-tolerance data Soil salinity EC at Productivity se Salinity decrease Common name Scientific name threshold 90% 75% 50% Reference per dS/m EC yield yield yield se increase (%)
Broccoli Brassica oleracea 5.5 8.3 2.8 9.1 3.9 1 Trefoil, big Lotus uliginosus 5.3 7.5 3.0 11.1 3.9 1 Green panic, Petri Panicum maximum 6.6 10.2 3.0 6.9 4.4 3 Pangola grass Digitaria decumbens (pentzii) 8.3 14.5 2.0 4.0 4.5 3 Bambatsi Panicum coloratum 9.3 17.1 1.5 3.2 4.6 3 Sudan grass Sorghum sudanense 8.6 14.4 2.8 4.3 5.1 1 Beet, garden Beta vulgaris 6.8 9.6 4.0 9.0 5.1 1 Dracaena Dracaena endivisa 6.7 9.5 4.0 9.1 5.1 1 Oats Avena sativa 6.3 7.5 5.0 20.0 5.5 9 Soybean Glycine max 6.3 7.5 5.0 20.0 5.5 1 Fescue Festuca elatior 8.6 13.3 3.9 5.3 5.8 1 Zucchini Cucurbita pepo melopepo 7.4 10.0 4.7 9.4 5.8 4 Sunflower Helianthus annuus spp. 6.5 7.5 5.5 25.0 5.9 9 Wheatgrass, Agropyron desertorum 9.8 16.0 3.5 4.0 6.0 1 crested Trefoil, birdsfoot Lotus corniculatus 7.5 10.0 5.0 10.0 6.0 1 Kikuyu grass, Pennisetum clandestinum 11.3 19.7 3.0 3.0 6.3 3 Whittet Buffel grass, Cenchrus ciliaris var. Gayndah 7.9 10.4 5.5 10.3 6.5 3 Gayndah Date Phoenix dactylifera 11.4 18.7 4.0 3.4 6.9 1 Barley, hay Hordeum vulgare 9.5 13.0 6.0 7.1 7.4 2 Barley, forage Hordeum vulgare 9.6 13.1 6.0 7.0 7.4 1 Wheat Triticum aestivum 9.5 13.0 6.0 7.1 7.4 1 Sorghum Sorghum bicolor 8.4 9.9 6.8 15.9 7.4 4 Buffel grass, Cenchrus ciliaris var. Nunbank 9.7 13.4 6.0 6.8 7.5 3 Nunbank Wheat, durum Triticum turgidum 10.3 15.0 5.7 5.4 7.6 4 Couch grass Cynodon dactylon 10.8 14.7 6.9 6.4 8.5 1 Beet, sugar Beta vulgaris 11.2 15.5 7.0 5.9 8.7 1 Wheatgrass, Agropyron cristatum 11.1 14.7 7.5 6.9 8.9 1 fairway Sorghum, crooble Sorghum almum 10.5 12.8 8.3 11.2 9.2 3 Urochloa Urochloa mosambicensis 10.5 12.5 8.5 12.4 9.3 3 Cotton Gossypium hirsutum 12.5 17.3 7.7 5.2 9.6 1 Wheatgrass, tall Agropyron elongatum 13.5 19.4 7.5 4.2 9.9 1 Barley, grain Hordeum vulgare 13.0 18.0 8.0 5.0 10.0 1 Rhodes grass, Chloris gayana 14.8 22.6 7.0 3.2 10.1 3 Pioneer Algerian ivy Hedera canariensis 1.0 * 6 Chinese holly Ilex cornuta 1.0 * 6 Heavenly bamboo Nandina domestica 1.0 * 6 Hibiscus rosa-sinensis cv. Hibiscus 1.0 * 6 Brilliante Lemon Citrus limon 1.0 * 6 Pear Pyrus spp. 1.0 * 6 Pittosporum Pittosporum tobira 1.0 * 6
Appendixes — Plant salt-tolerance data 131 Soil salinity EC at Productivity se Salinity decrease Common name Scientific name threshold 90% 75% 50% Reference per dS/m EC yield yield yield se increase (%)
Prune Prunus domestica 1.0 6 * 6 Raspberry Rubus idaeus 1.0 6 * 6 Rose Rosa spp. 1.0 6 * 6 Guava, pineapple Feijoa sellowiana 1.2 6 * 6 Bottlebrush Callistemon viminalis 1.5 6 * 6 Star jasmine Trachelospermum jasminoides 1.6 6 * 6 Lantana Lantana camara 1.8 1 * 1 Arbor-vitae Thuja orientalus 2.0 6 * 6 Cauliflower Brassica oleracea 2.5 6 * 6 Pea Pisum sativum L. 2.5 6 * 6 Squash Cucurbita maxima 2.5 6 * 6 Olive Olea europaea 4.0 6 * 6 Pomegranate Punica granatum 4.0 6 * 6 Fig Ficus carica 4.2 6 * 6 Phalaris Phalaris tuberosa (aquatica) 4.2 6 * 6 Rosemary Rosmarinus lockwoodii 4.5 6 * 6 Natal plum Carissa macrocarpa 6.0 6 * 6 Kale Brassica campestris 6.5 6 * 6 Safflower Carthamus tinctorius 6.5 6 * 6 Euonymus japonica var. Euonymus 7.0 6 * 6 grandiflora Bougainvillea Bougainvillea spectabilis 8.5 6 * 6
132 Appendixes — Plant salt-tolerance data Pasture species for saline soils
The following table (Table 48) lists plants considered Notes on saltbush and samphire suitable for planting on saline soils in Queensland (I. species Christiansen, pers. comm.; Townson & Roberts 1992). Information is included on growth habit, propagation, Atriplex (saltbush) shrubs enhance nutrient cycling, tolerance to waterlogging and salinity, and pasture increasing fertility in the mounds under individual characteristics. The species are divided into four bushes and creating favourable microniches for other groups: species. Pasture production beneath the shrubs is • grasses for severely saline soils greater than in the surrounding area (Mott & McComb 1974). Growth of ephemerals is also promoted under • grasses for highly saline soils Atriplex shrubs (Wilcox 1979). When sown, saltbush • grasses for less saline soils (such as the periphery plants should be spaced to allow other pasture of saline areas) species to establish in the intervening area. • other plants for saline soils. Saltbush is best regarded as a protein supplement to Grazing management is particularly important in dry grasses or cereal stubbles. For instance, sheep fed saline areas. Natural regeneration after stock have on saltbush alone are likely to lose weight (Warren et been excluded or stocking rates decreased is often al. 1990). Provided a plentiful supply of fresh water significant. When salt-tolerant pastures are planted, is available, cattle productivity on (supplemented) stock should ideally be excluded for an initial period— saltbush pasture is similar to that of sheep (Wilson & generally one to two years depending on conditions— Graetz 1980). to allow pasture species to establish and achieve Because samphires are high in soluble salts, these satisfactory growth. species are more suitable for grazing by sheep than by cattle or other stock. Samphire grazing should be diluted with alternative fodder such as crop stubble, grass or hay, and a plentiful supply of fresh water should be available. Samphire stands do not tolerate heavy grazing (Malcolm & Cooper 1974). Grazing on samphires is best restricted to late summer and autumn so that the plants can maintain normal summer growth and set seed.
Appendixes — Pasture species for saline soils 133 Table 48. Plants considered suitable for saline conditions in Queensland (I. Christiansen, pers. comm.; Townson & Roberts 1992).
Grasses for severely saline soils
Waterlogging and Species Growth habit Pasture features Propagation salinity tolerance Brown beetle grass Tufted, semiaquatic Often found in Highly palatable and Does not set viable Diplachne fusca grass up to 1.5 m high. flooded depressions nutritious. (Regarded seed; best established Leaves are soft and or in areas where the as a weed of rice crops from rooted slips. succulent. Forms a watertable is close and waterways.) Active growth in dense mat. Generally to the surface. Very summer. found growing only in high salt tolerance. patches. Tolerates drought and fire. Salt-water couch Slow growing, mat Very resistant to high Palatable, readily Seed viability very Paspalum distichum forming. salt concentrations. grazed. Tolerates low and not available (formerly P. Suitable for drainage strategic grazing once commercially; all vaginatum) lines or areas where established. plantings to date continuous salty have used rooted seepage keeps the clumps, runners and ground moist most cuttings. Has been of the time. Fairly observed to spread resistant to frost and and stabilise a salt- high temperatures affected waterway near Monto and Kingaroy, and to spread slowly downstream. Marine couch Fine-leaved, mat Establishes and Considered a valuable Establishes well from Sporobolus virginicus forming grass, 5–40 spreads well on highly pasture for fattening rooted clumps. Needs cm high. saline soils with high cattle. Palatable and plentiful moisture watertables. Tolerates nutritious. Tolerates for good growth but extremely high salt strategic grazing once is able to survive dry levels. Found naturally established. periods. Seeds do not in areas where the germinate readily watertable is high or which are subject to periodic flooding or marine inundation. Responds well to controlled burning. Buffalo grass Hardy perennial grass. Tolerates high salinity Palatable when young; Plant from rooted Stenotaphrum Spreads vigorously by in moist, swampy can be made into runners, dig or disc secundatum runners; roots readily soils. Tolerates frost, useful silage. Best harrow then roll into at stem joints. short dry periods, grazed every second the soil. Does not set flooding and shade. week to 6 cm; recovery seed. is slow if grazed shorter than this.
134 Appendixes — Pasture species for saline soils Grasses for highly saline soils
Waterlogging and Species Growth habit Pasture features Propagation salinity tolerance Rhodes grass Perennial, tufted grass Most salt-tolerant Highly valued as a By seed. Chloris gayana up to 1 m high. Tough, pasture species pasture species. wiry, leafy runners root available commercially. Cultivar Pioneer is the and shoot readily at Suggested for erosion most salt tolerant but the nodes and watertable salting the least palatable areas on a wide range when mature; produces of soils. Tolerates abundant seed. Some frost and drought. Can Katamboora cultivars extract water to 4.25 m. are salt tolerant and palatable. Common or green Perennial grass which Tolerates moderate Very palatable and Can be included in the couch forms a tough mat. to high levels of soil nutritious if fertilised seed mixture under Cynodon dactylon salinity, particularly in and growth kept short. most conditions except subtropical conditions. Good soil binder in low rainfall and Can be highly to prevent erosion. very salty areas. Once productive on very Resistant to heavy established, spreads saline soils. Tolerates grazing. quickly by rhizomes drought. Recovers from and stolons. frost. Curly windmill grass Tufted perennial grass Tolerates extreme Varieties found Readily establishes Enteropogon acicularis up to 1 m high, but soil salinity. Tolerates on heavy soils are (naturally) on bare usually less. Grows in drought. valuable fodder; taller, ground and in clumps up to 30 cm coarser variety found waterways. wide with a strong, on sandy soils is only fibrous root system. moderately palatable, but is useful when other feeds become scarce. Does not tolerate heavy grazing.
Grasses for less saline soils (such as the periphery of saline areas)
Waterlogging and Species Growth habit Pasture features Propagation salinity tolerance Pangola Stoloniferous; summer Does not tolerate Highly palatable and By sprigs or roots Digitaria decumbens growing. extreme salinity but is nutritious when young. from which it spreads useful for less saline Makes good silage if rapidly. Does not set margins. Tolerates cut before it becomes viable seed. temporary flooding stemmy. only. Susceptible to frost but recovers well when weather warms. Will survive drought once established. Tall fescue grass Winter growing grass. Good for margins of Good pasture species. Vegetative or seed. Festuca arundinacea Will gradually colonise saline areas and wet Sets viable seed. surrounding area. toeslopes.
Para grass Perennial grass up to 2 Commonly found in Sensitive to frost. Set seed not generally Brachiaria mutica m tall with long, hairy swampy areas. Grows Young grass is very viable, so vegetative leaf blades. well in areas that are palatable. Valuable as planting is usually flooded occasionally or feed in the dry season. necessary. Planting in seepage areas. Often material should be found on deep loams reduced to 20–30 over saline clays and cm lengths, spread on marine floodplains. over the area and Can be used in high disced into the soil. rainfall areas (more Irrigation after planting, than 800 mm/year). if available, is most beneficial.
Appendixes — Pasture species for saline soils 135 Other plants for saline soils
Waterlogging and Species Growth habit Pasture features Propagation salinity tolerance River saltbush Bushy, perennial shrub. Grows vigorously in Good forage, recovers Best established from Atriplex amnicola extremely saline areas well from grazing. seedlings or cuttings. provided sufficient High protein, low moisture is available. carbohydrate. Tolerates waterlogging. Wavy leaf saltbush Bushy, low-growing Grows well on Generally not as Establishes well from Atriplex undulata shrub. drier sites. Not productive as seed. Susceptible to recommended for A.‑amnicola. Recovers dieback disease. waterlogged areas. well from grazing. Readily grazed by sheep. High protein. Old man saltbush Upright growth habit. Tolerates very Less palatable than Grows rapidly from Atriplex nummularia Leafy. high salinity. Not A.‑amnicola and seedlings even in low tolerant of prolonged A.‑undulata. High rainfall conditions. waterlogging. Tolerates protein. Seeds should be drought. washed with running water for 2 to 4 hours before sowing to leach out germination inhibitors. Susceptible to Phytopthera (root rot). Grey saltbush Both prostrate and Tolerates moderate Variable palatability. Spreads rapidly. Atriplex cinerea upright forms. waterlogging. High protein. Queensland bluebush Upright, open shrub. No information Useful as a drought- Volunteers readily in Chenopodium available. resistant fodder. areas spelled from auricomum stock.
Ruby saltbush Dense, rounded bushy Grows well on highly Readily grazed with Volunteers readily after Enchylaena tomentosa shrub with short, saline soils. Tolerates very high digestibility. grazing pressures have succulent leaves, up to moderate waterlogging. Does not withstand been removed. Fresh 1.5 m high. Flowers and continuous, heavy seed (encased in pink fruits during most of grazing. Sweet berries berry) germinates well. the year. are edible.
Coastal pigface Succulent, prostrate, Good coloniser of A good pioneer of Establishes by Sesuvium perennial herb. severely saline, bare severely saline areas, plant pieces. Once portulacastrum Spreads by long stems ground, creating more paving the way for established, spreads flat on the ground. favourable niches in other species to well by runners. Does which other plants can become established. not compete well establish. Tolerates with other species, waterlogging. but will re-establish if competing species fail. Samphire Low-growing, leafless Colonises severely High protein content. Establishes well from Halosarcia spp. shrub. May cover affected areas well, Readily grazed surface-sown seed; considerable ground and can improve soil provided sufficient plant pieces that hold area. conditions for other other, less saline feeds seed can be spread. species to establish. are also available. Tolerates extreme waterlogging. Swamp rat-tail grass Spreads rapidly over Grows well in saline Good early coloniser Plant as rooted clumps Sporobolus mitchelli bare ground by means seepages. but takes some time or runners. of long runners. to produce good ground cover. Tolerates strategic grazing once established.
Note: Refer to notes on saltbush and samphire species at the beginning of this section.
136 Appendixes — Pasture species for saline soils Tree species for salinity management
The information in Table 49 has been collated from 5. Potential uses: the results of research trials conducted in Queensland s/s shade/shelter and other States, supported by information based on fge forage the experience of Forestry officers and researchers in establishing and observing tree planting projects wbk windbreaks around Queensland (Hinchley 1994). (Further frm farm timber information on selecting, establishing and maintaining cbt cabinet or craft timber trees is provided in Tree planting page 104.) pol poles/sawlogs This information, along with more detailed information oil oil/tannin/chemicals on tree species, is now available on the Internet. The hny honey Queensland Tree Selector
Appendixes — Tree species for salinity management 137 Table 49. Trees suitable for growing in saline and waterlogged conditions and for use in salinity management (Hinchley 1994).
Tolerance Potential Height6 Info Scientific name Water- Suit Rainfall Origin7 Salinity1 Sodicity1 Frost2 uses5 (m) origin8 logging1 SDS3 zone4 Acacia frm, cbt, M L L L M 28 Q F,G,E aulacocarpa pol, hny Acacia fge, frm, H L H N ✓ H 20 Q F,G,E auriculiformis cbt, pol, oil Acacia L L M L 7 H frm, cbt, pol 12 Q F,E crassicarpa Acacia leptocarpa L L ? N 7 M fge, frm, cbt 7 Q F,G,E s/s, wbk, Acacia mangium L L L L 7 H 25 Q G,E cbt, pol Acacia s/s, wbk, M M L H H 25 Q F,G,E melanoxylon cbt, pol Acacia pendula L M M H L s/s, fge, cbt 6 Q G,E fge, wbk, Acacia salicina H L H H ✓ L 12 Q G,E cbt, pol Acacia saligna M L L H L fge, wbk 4 A G,E Acacia s/s, fge, H M H H ✓ L 8 Q G,E stenophylla frm, cbt Atriplex spp. H L M H ✓ L fge 2 Q E Callistemon H M L H ✓ H wbk 4 A E linearis Callistemon H M L L ✓ M wbk 2 Q E montanus Callistemon H M L H ✓ H wbk 3 A E phoenicius Callistemon H M L H ✓ H wbk 3 Q E rigidus Cassia brewsteri M L M H M s/s 8 Q G,E Casuarina cristata H M M H ✓ L s/s, wbk 20 Q E Casuarina s/s, fge, H H L H ✓✓ H 30 Q F,G,E cunninghamiana wbk, cbt Casuarina M M H L ✓ H s/s, fge 15 Q G,E equisetifolia Casuarina glauca VH H M H ✓✓ M s/s, wbk 20 Q F,G,E Eucalytpus H M M H ✓ L s/s, frm, pol 25 Q G,E argophloia Eucalyptus H L H M ✓ H s/s 20 Q F,E brassiana Eucalyptus M M ? H VL s/s, frm 15 WA G,E brockwayii s/s, fge, Eucalyptus H H H H ✓✓ VL wbk, frm, 30 Q F,G,E camaldulensis pol, hny Eucalyptus M L L L M s/s, frm, pol 30 Q F,G,E citriodora Eucalyptus L L L L 7 H s/s, frm, pol 35 Q G,E cloeziana Eucalyptus curtisii H L H H ✓ L s/s, pol 6 Q E
138 Appendixes — Tree species for salinity management Tolerance Potential Height6 Info Scientific name Water- Suit Rainfall Origin7 Salinity1 Sodicity1 Frost2 uses5 (m) origin8 logging1 SDS3 zone4 Eucalyptus M L L H 7 H s/s, pol 35 Q F,G,E grandis Eucalyptus s/s, frm, L L L L 7 H 30 F,E intermedia hny Eucalyptus M H ? H L s/s, hny 20 Q G,E largiflorens Eucalyptus M L L H L hny 20 A G,E leucoxylon Eucalyptus H M M H ✓ L s/s, hny 20 A E longicornis Eucalyptus H L M L H pol, hny 30 Q G,E maculata s/s, wbk, Eucalyptus M M M H ✓ L frm, pol, 25 Q F,E melliodora hny Eucalyptus s/s, frm, H L H H ✓ VL 25 Q F,G,E microtheca pol, hny Eucalyptus s/s, wbk, H M M H ✓✓ H 20 Q F,G,E moluccana pol, hny Eucalyptus wbk, frm, L L ? L 7 H 30 NQ E paniculata hny s/s, pol, Eucalyptus pellita M M L L H 30 NQ G,E hny Eucalyptus s/s, wbk, L L L L 7 H 35 Q G,E pilularis frm, cbt, pol Eucalyptus M M ? H L hny 6 WA G,E platypus var. Eucalyptus H M ? H ✓ L s/s, frm 20 Q F,G raveretiana s/s, wbk, Eucalyptus H H L L ✓ VH frm, cbt, 25 Q F,G,E robusta pol, hny Eucalyptus s/s, wbk, L L L L 7 VH 30 Q G,E saligna pol, hny Eucalyptus s/s, frm, H L M H ✓ L 30 Q F,E sideroxylon pol, oil, hny Eucalyptus s/s, wbk, M M ? H L 6 A G,E spathulata oil Eucalyptus frm, pol, H H H H ✓✓ M 30 Q F,G,E tereticornis hny Eucalyptus H L H H M frm 25 Q E tessellaris Grevillea robusta M L L L 7 M s/s, cbt, pol 25 Q G,E Leptospermum L L L L 7 M wbk 3 G,E petersonii Leptospermum H H L H ✓✓ L wbk 2 Q E polygalifolium Leucaena M L L L M fge 6 E F,E leucocephala s/s, wbk, Lophostemon L L L L 7 H frm, cbt, 30 Q G,E confertus pol, hny
Appendixes — Tree species for salinity management 139 Tolerance Potential Height6 Info Scientific name Water- Suit Rainfall Origin7 Salinity1 Sodicity1 Frost2 uses5 (m) origin8 logging1 SDS3 zone4 Melaleuca s/s, wbk, M H L L ✓ H 7 Q G,E alternifolia oil s/s, wbk, Melaleuca arcana H ? ? N M 8 F hny Melaleuca s/s, wbk, M M ? N M 8 Q G,E argentea hny Melaleuca s/s, wbk, M L M L M 6 Q G,E armillaris hny Melaleuca s/s, wbk, H VH M H ✓✓ M 8 Q F,G,E bracteata oil, hny Melaleuca s/s, wbk, H ? ? N M 8 Q F,G cajeputi oil Melaleuca L M ? ? 7 H s/s, wbk 8 A F,G,E dealbata Melaleuca H H L L ✓✓ M wbk 2 A E decussata Melaleuca s/s, wbk, L M ? H M 4 Q G,E lanceolata hny Melaleuca H L L L H 2 A G,E lateritia s/s, wbk, Melaleuca H H M L ✓✓ H frm, pol, oil, 20 Q F,G,E leucadendra hny Melaleuca s/s, wbk, M H M H ✓ H 10 Q G,E linariifolia oil, hny Melaleuca nodosa M VH M H ✓✓ M hny 3 Q F,E Melaleuca s/s, wbk, M H M L ✓✓ M 20 Q F,G,E quinquenervia oil, hny Melaleuca H H L H ✓✓ H hny 1 Q G,E thymifolia Melaleuca L H L L H hny 15 Q E viridiflora s/s, pol, Melia azedarach M L M H ✓ M 25 Q E hny Metrosideros M L ? L VH pol 20 Q G,E queenslandica Pinus caribaea s/s, wbk, L L M L 7 H 30 E G,E var. hondure 9 pol Pittosporum M L M H M s/s, fge 6 Q E phylliraeoides Syzygium forte M M ? N ✓ VH s/s 20 Q E spp. forte Tamarix aphylla 10 H L ? ? 7 L s/s, wbk 20 E G Tipuana tipu 9 L L L H 7 M s/s, fge 15 E F,E
140 Appendixes — Tree species for salinity management Useful software packages
Table 50. Summary listing of software packages relevant to salinity investigations and property management decisions.
Software package Product and features Sources and contacts
Climate/rainfall information AUSTRALIAN RAINMAN Provides and can analyse rainfall information for nearly 4‑000 locations DEEDI book sales throughout Australia, incorporating the likely effects of the Southern Oscillation Index (SOI) and of Sea Surface Temperatures (SST) in the Indian Ocean on rainfall predictions. Package includes a book, Will It Rain?, which explains how the SOI and Indian Ocean SST influence weather in Australia, and how farm and pastoral managers can use this information to make informed decisions. Salinity-related calculations SALF–SALFCALC Designed to ‘make sense’ of soil salinity data. Using soil profile data, DERM measures of root zone salinity, leaching fraction and relative crop yield can be calculated. Also converts between salinity measurements at different
water contents (EC1:5, ECse and ECs). Output can be stored in files for use with other packages. Catchment hydrology TOPOG-IRM Combines information about soils and vegetation with contour maps to CSIRO Land and Water predict how and where water flows through a catchment. Can be used to predict the effects of tree clearing or planting or changes to farm plans on a flow of groundwater, on a catchment scale. Results are presented three- dimensionally. Requires detailed data inputs. SWAGSIM Links above-ground processes with subsurface processes. Simulates CSIRO Land and Water recharge and watertable response across a region having a patchwork of crops and water-use patterns. Models regional watertable fluctuations, locates recharge and discharge zones, and calculates the rates of these processes; can also be used to plan pumping for salinity control and to estimate groundwater discharge into streams. Groundwater modelling MODFLOW Can be used to model groundwater systems and to explore the effect of United States changes to the groundwater (for instance, resulting from the extraction Geological Survey of water through pumping, or increased recharge through tree clearing). (source code) Requires input of detailed data on the catchment under study. Various distributors (compiled and enhanced versions) Crop water balance PERFECT Can be used to examine how crop water use matches available water and to DERM (Productivity, Erosion, provide information for planning future cropping programs. Compares the DEEDI book sales Run-off Functions to water use of alternative cropping strategies, assessing the productivity and Evaluate Conservation economic performance of each strategy. Uses a cropping system simulation Techniques) model to analyse the risks that soil erosion poses for long-term crop production under different conditions.
Appendixes — Useful software packages 141 Software package Product and features Sources and contacts
Irrigation management and crop selection SALF–SALFPREDICT Designed for predicting the effects of different irrigation regimes on a DERM number of crop and other plant species. From information about water quality, soil properties and rainfall, the program estimates leaching fraction (the amount of water draining below the root zone) and salinity in the root zone, and then predicts the likely effect on crops grown under these conditions. Output can be stored in files for use with other packages. SODICS Models solute dynamics in irrigated clay soils. Can be used to assess DERM the potential salinity hazard of soils in a range of dryland and irrigated situations and to assess the impact of tree clearing on deep drainage. Calculates deep drainage between two times in a soil profile from soil salinity data. Future changes in soil salinity with time in the profile can then also be calculated. MEDLI Uses a number of models to consider the range of factors involved in DERM (Model for Effluent designing and operating sustainable land disposal systems for effluent Disposal using Land from a range of intensive rural industries (such as piggeries, cattle feedlots, Irrigation) abattoirs, dairy sheds and sewage treatment plants). Supports decision making from a range of options. SWAGMAN WHATIF Education package. Develops an understanding of the interactions between CSIRO Land and Water (Salt, Water and shallow watertables, crops, irrigation and salinisation. Package includes Groundwater a booklet, Understanding Salt and Sodium in Soils, Irrigation Water and Management) Shallow Groundwaters. SWAGMAN OPTIONS Uses a framework of submodels (hydrogeology, soils, irrigation, soils, CSIRO Land and Water agronomy and economics) to evaluate cost-effective partial solutions on a number of scales (farm, sub-catchment and regional) for managing watertable rise and salinisation in irrigated areas (particularly in relation to growing rice). Gross margins are maximised and recharge minimised while maintaining soil salinity below critical levels, using a series of optimisation routines and a groundwater simulation routine. SIRAG Irrigation decision support for deciding how much water to apply and when. CSIRO Land and Water Component versions deal with irrigation scheduling for annual field crops and for orchard crops. Can be used to forecast irrigations in the current season or to evaluate irrigation management in past seasons. RUSTIC Tool for designing farm dams and water harvesting equipment, preparing DERM (Runoff, Storage and irrigation management plants, selecting cropping strategies and assessing Irrigation Calculator) existing irrigation/cropping systems. Can be used to calculate runoff values, performance of storage or water harvesting installations, size of land and balancing storage necessary for land disposal of effluent, reliability of irrigating from a number of sources, and to compare the performance of crops under irrigation and not under irrigation. WATERSCHED An irrigation management aid for field crops for predicting future irrigation DEEDI book sales dates and amounts to apply, according to crop water use. Pumping options Pump it Interactive spreadsheet program designed for land use planners and CSIRO Land and Water advisers that allows the user to select the best pumping strategy to reduce rising water levels (if enhanced discharge is the optimal salinity management solution). Provides information on effects of windmill pumping, siting pumping wells, pump and windmill size, optimum pumping rates and times and disposal options for pumped saline effluent.
142 Appendixes — Useful software packages SALF To operate SALFPREDICT, the following information is required: The SALF for Windows software package incorporates • annual rainfall (in mm) the models SALFPREDICT and SALFCALC. This version of the software has several useful features: • EC of the water to be used for irrigation (in an irrigation situation) (in dS/m) • Data manipulation functions simplify the export • cation exchange capacity of the soil (in cmole /kg, and import of data in various formats. For instance, c SALF can generate Excel spreadsheet formatted equivalent to meq/100 g) files which enables data to be exchanged with • clay content of the soil (as a percentage) other applications with ease. • exchangeable sodium in the soil at 0.9 m depth
• SALF integrates database management tools for (nominal bottom of the root zone) (in cmolec /kg or project and site evaluations based on SITES (Soil meq/100 g). Information Transfer and Evaluation System) Data entered into SALFPREDICT and results generated consistent with a national standard for soil by the program can be stored in associated files for database design. This ensures that data entered further reference. into the SALF database will be in a form suitable for future data transfer. Limitations of SALFPREDICT • SALF incorporates a graph package for graphical presentations of calculated data and illustrating EC In developing the SALFPREDICT model, some and Cl versus depth over the root zone. assumptions had to be made. SALFPREDICT is not reliable for data that do not agree with these The minimum system requirements for SALF for assumptions. The following riders need to be Windows are: considered when using SALFPREDICT: • Intel 386-based PC or higher, with 4Mb of RAM • Climate and rainfall—The model is based on steady • Microsoft Windows 3.1, Windows NT, or Windows 95 state conditions and requires the entry of average • hard disk with at least 3Mb free rainfall data. Thus the model predicts average • mouse or pointing device. values that correspond to steady state conditions. The model does not accommodate short-term rainfall fluctuations, and is not appropriate for SALFPREDICT changes over periods of less than 10 years. In addition, SALFPREDICT was developed using data SALFPREDICT is used to predict the effects of irrigation for conditions receiving average annual rainfall on soil root zone salinity, leaching fraction and plant of 200 to 2 000 mm. The model will not provide salinity response, based on soil properties and salt reliable estimates for average annual rainfall balance. values outside this range. SALFPREDICT is based The model used by SALFPREDICT, described and on conditions in summer rainfall areas, and will developed in Shaw and Thorburn (1985a, 1985b), is underestimate the leaching fraction in winter a long-term steady state prediction of the potential rainfall areas. change in root zone salinity and leaching fraction with • Local conditions—SALFPREDICT inputs are depth changes in water inputs. The model incorporates soil weighted averages of rainfall and irrigation on particle packing theory, rainfall amount, the role of an annual basis. For some crops and conditions, exchangeable sodium and electrolyte content on soil short-term salinity problems may become apparent, permeability, and the influence of clay content and particularly in dry years, in response to seasonal mineralogy on soil behaviour. Over 700 soil profiles variations in crop growth, rainfall and irrigation from a wide range of rainfalls were used to drive the application. This is not accounted for. A rough relationships which were validated in three irrigated estimate can be made by changing the irrigation– areas in Queensland. rainfall data to reflect the dry year. Plant varieties For the development of the model, refer to Shaw and and local conditions, particularly evaporative Thorburn (1985a) and Shaw and Thorburn (1985b). demand, may result in plant responses that differ The plant salt-tolerance data used in SALFPREDICT are from those incorporated into SALFPREDICT. taken from published relationships and recalculated • Soil properties—Relationships for some clay in some cases. These data are presented in Shaw et and CEC/clay ratio groups are not provided in al. (1987). SALFPREDICT because of the limited occurrences of these soils in Queensland. If the user selects one of these soils, SALFPREDICT will use an algorithm to select a soil group with similar characteristics, so these results must be considered as
Appendixes — Useful software packages 143 approximations only. SALFPREDICT states the clay/ SALFCALC CCR group used in the calculation. If the CEC/ clay ratio is less than 0.25, a soil will most likely SALFCALC has been designed to help ‘make sense’ be acid. These soils are under-represented in the of soil salinity data. SALFCALC can be used to convert soil groups used in deriving the relationships raw data to measures of salinity that have direct for the model. For these soils, SALFPREDICT will relationships with plant yield data and soil leaching underestimate leaching and overestimate root zone processes. Leaching fraction and relative plant yield salinity. can be estimated. • Leaching fraction—The leaching fraction is To operate SALFCALC, the following information is calculated at field water content, which is required for each site: calculated as 2.2 times drier than saturation. This is • name of the crop to be grown (to be selected from a based on the essential cessation of downward flux list supplied by the program) of water at ‘field capacity’. The program converts • root zone depth for the crop (in cm) EC to EC . More accurate methods are being s se • EC data for the soil profile, at sampled depth developed. 1:5 intervals (in dS/m) • Measure of salinity—Because the sum of all • Cl data for the soil profile, at sampled depth salts present has an effect on soil permeability, 1:5 electrical conductivity has been used to represent intervals (as % by weight, or in mg/kg) salinity rather than chloride. If an irrigation water • air dry water content, or clay content, or CEC, or –33 contains significant calcium associated with sulfate kPa water content, or –1500 kPa water content (or soil texture, although this is less accurate). (SO4) and/or bicarbonate (HCO3) or sodium as bicarbonate or carbonate (CO3), SALFPREDICT will From this initial information, SALFCALC will calculate: overestimate the root zone salinity. This is because • conversions between salinity measurements (EC) at the model assumes no precipitation of salts as the different water contents—EC , EC and EC soil dries. 1:5 se s • average and water uptake weighted root zone • Root zone characteristics—The model assumes salinity average soil properties in a root zone with a depth • leaching fraction (fraction of applied water and of 0.9 m. For soils with strong texture contrast and rainfall moving below the root zone) deep sandy A horizons, SALFPREDICT will provide less reliable results. • plant-available water capacity of the soil • pH—The model was derived mainly for soils in • relative yield for a crop (selected from a list the semiarid areas, which are dominantly neutral provided by the package). to alkaline in pH. For soils with pH less than 4.5, SALFPREDICT results will underestimate deep Limitations of SALFCALC drainage due to the increased soil stability resulting Because the method of measuring saturation from exchangeable aluminium under these percentage is prone to inaccuracy, SALFCALC uses conditions offsetting the effects of exchangeable surrogate estimates of saturation percentage. sodium. Considering the errors introduced by these estimates • A non-linear correction has been applied to address and the method of determining plant salt tolerance, the effect of increasing EC on soil leaching, based SALFCALC’s predictions will not be precise and should on field work in the Lockyer Valley. This is not be considered ± 20% at best. necessarily applicable to all soils.
144 Appendixes — Useful software packages Salinity publications for further reference
Salinity investigations in Gill, Jill 1984, Determining the quality of water for irrigation in Queensland, Department of Primary Queensland past and present Industries, Queensland, Ref. note R1, January 1984. This list is intended only as an initial guide to known Gill, Jill 1979, Assessment of water analysis results for regional investigations and salinity research work in irrigation in Queensland, Department of Primary Queensland. All too often, relevant information is not Industries, Queensland, Ref. note R37, July 1979. published in a form that is widely available, and Gordon, Ian (ed.) 1991, A survey of dryland and subsequent researchers, being unaware of the irrigation salinity in Queensland, Information Series previous work, are unable to take advantage of it. QI91034, Land Management Research Branch, Much of the information listed here may be available Department of Primary Industries, Queensland. only from libraries or from the authors themselves. Hughes, Keith 1979, Assessment of dryland salinity In general, the reports are divided into localities in Queensland, Division of Land Utilisation which are listed in geographical order, progressing Report 79/7, Department of Primary Industries, approximately from south to north and from east Queensland. to west. Within each locality, reports are listed in Saltwatch ‘91–’93, summary report 1994, Natural alphabetical order by the surname of the first author. Resource Management Unit, Department of Primary Where possible, authors’ first names have been Industries, Queensland, joint initiative with provided to facilitate personal contact. Department of Education, Queensland. Shaw, Roger 1988, ‘Predicting deep drainage in the State-wide or multiple areas soil from soil properties and rainfall’, Soil Use and Management, 4:120–123. Beetson, Trevor & Gordon, Ian 1991, ‘Role of trees Shaw, Roger & Thorburn, Peter 1985, ‘Prediction of in alleviating secondary salinity: The current leaching fraction from soil properties, irrigation position in Queensland’, The role of trees in water and rainfall’, Irrigation Science, 6:73–83. sustainable agriculture—A National Conference, 30 September–3 October 1991, Albury Convention Thorburn, Peter, Rose, Calvin, Shaw, Roger & Yule, Centre, National Agroforestry Working Group. Don 1990, ‘Interpreting solute dynamics in irrigated soils, I. Mass balance approaches’, Irrigation Bevin, Peter & Shaw, Roger 1980, ‘Queensland salinity Science, 11:199–207. problems in irrigation areas’, Bulletin, Australian National Committee for Irrigation and Drainage, Wreczycki, R.J. 1968, ‘Findings on boron content of Special Issue, August 1980. Queensland waters’, Queensland Agricultural Journal, 94:331. Brebber, Lindsay 1991, Saltwatch ‘91: Summary of collected data, Project Report QO92005, Natural Resource Management Unit, Department of Primary Inglewood Industries, Queensland. Gordon, Ian 1994, ‘Terrica: Salt at faults and folds’, Gill, Jill 1986, ‘Water quality for agriculture in Case study in Saltwatch Activity Book, Training Queensland: A review of methods of interpretation Series QE94003, Land Conservation, Department of of water analysis results and a survey of the Primary Industries, Queensland, pp. 43–45. geographical distribution of agricultural water Harris, Graham 1986, ‘Salinity in the Inglewood quality in Queensland’, Bulletin QB86004, Shire’, in Landscape, soil and water salinity, Agricultural Chemistry Branch, Department of Proceedings of the Darling Downs Regional Primary Industries, Queensland. Workshop, Toowoomba, March 1986, Conference Gill, Jill 1985, ‘Queensland water quality survey’, in and Workshop Series QC86001, pp. B3-1 to B3-13, Landscape, soil and water salinity, Proceedings of Department of Primary Industries, Queensland. Lockyer Moreton Regional Workshop, Ipswich, June Thorburn, Peter, Shaw, Roger & Gordon, Ian 1992, 1985, Conference and Workshop Series QC85004, ‘Modelling salt transport in the landscape’, in pp. C1-1 to C1-12, Department of Primary Industries, Modeling Chemical Transport in Soils, ed. H. Queensland. Ghadiri & C.W. Rose, Chapter 4, pp. 145–190, Lewis Publishers, CRC Press Inc., Florida.
Appendixes — Salinity publications for further references 145 Lockyer—Ipswich Thorburn, Peter, Shaw, Roger & Ahern, Col 1984, ‘A comparison of leaching estimates in irrigated soils Ahern, Col, Shaw, Roger & Thorburn, Peter 1984 in the Lockyer Valley, Queensland’, Proceedings of ‘Differences in chemical and physical properties the National Soils Conference, Brisbane, May 1984, between soil layers of black earths on alluvia in the Australian Society of Soil Science, Brisbane, p. 286. Lockyer Valley, Queensland’, Abstract of conference Truong, Paul, Gordon, Ian & McDowell, Murray 1991, presentation, in Proceedings of the National Soils Effects of soil salinity on the establishment and Conference, Brisbane, May 1984, Australian Society growth of Vetiver zizanioides (L.), World Bank of Soil Science, Brisbane, p. 180. Special Publication. Christiansen, Ingrid 1993, Distribution and growth Zinn, Peter 1985, ‘Development of groundwater in of plants in relation to soil salinity in south-east the Lockyer Valley’, in Landscape, soil and water Queensland, BSc (Honours thesis), Department of salinity, Proceedings of the Lockyer–Moreton Botany, University of Queensland, St Lucia. Regional Workshop, Ipswich, June 1985, Conference Doherty, John 1992, Some aspects of small-catchment and Workshop Series QC85004, pp. D3-1 to D3-5, groundwater hydrology, Project Report QO92001, Department of Primary Industries, Queensland. Department of Primary Industries, Queensland. Gardner, E. (Ted) 1985, ‘Hydro-salinity problems in the Lockyer Valley—real and perceived’, in Landscape, Darling Downs soil and water salinity, Proceedings of the Lockyer– Doherty, John & Stallman, Adrian 1994, Pump Moreton Regional Workshop, Ipswich, June 1985, test and soil profile analyses for the Brymaroo Conference and Workshop Series QC85004, pages Catchment, Project Report Series QO94007, Natural D1-1 to D1-9, Department of Primary Industries, Resource Management Unit, Department of Primary Queensland. Industries, Queensland. Hughes, Keith 1985, ‘Notes on seepage salting at Doherty, John & Stallman, Adrian 1992, Land Queensland Agricultural College Darbalara Farm’, in management options for a salt-affected catchment Landscape, soil and water salinity, Proceedings of on the Darling Downs, Project Report QO92010, the Lockyer–Moreton Regional Workshop, Ipswich, Division of Land Management, Department of June 1985, Conference and Workshop Series Primary Industries, Queensland. QC85004, pp. D2-1 to D2-5, Department of Primary Gordon, Ian & Shaw, Roger 1994, ‘Brymaroo: Salinity Industries, Queensland. and recycling’, Case study in Saltwatch Activity Hughes, Keith 1982, Summary report on salinity Book, Training Series QE94003, Land Conservation, in the Kalbar Area, unpublished internal report, Department of Primary Industries, Queensland, pp. Division of Land Utilisation, Department of Primary 36–40. Industries, Queensland. Hughes, Keith 1986, ‘Dryland salting overview— Hunt, Keryn 1994, ‘Boonah: The outfield’s fast’, Case Darling Downs area’, in Landscape, soil and water study in Saltwatch Activity Book, Training Series salinity, Proceedings of the Darling Downs Regional QE94003, Land Conservation, Department of Workshop, Toowoomba, March 1986, Conference Primary Industries, Queensland, p. 35. and Workshop Series QC86001, pp. B8-1 to B8-10, McNeil, Vivienne, Poplawski, Wojciech & Gardner, E. Department of Primary Industries, Queensland. (Ted) 1991, Salinity problems affecting irrigation Huxley, Bill 1986, ‘Regional hydrology and water in the Lockyer Valley, Queensland, Australia, quality characteristics of the Darling Downs’, in presented at the conference on Irrigated induced Landscape, soil and water salinity, Proceedings physical and chemical changes in groundwater and of the Darling Downs Regional Workshop, surface water, Vienna, Austria. Toowoomba, March 1986, Conference and Powell, Bernie, Shaw, Roger & Roberts, Max 1985, Workshop Series QC86001, pp. B11-1 to B11-10, ‘Factors for evaluation of land for sustainable Department of Primary Industries, Queensland. irrigation in the Lockyer Valley’, in Proceedings Kalma, Steve 1995, An evaluation of airborne Fourth Australian Soil Conservation Conference, geophysics for salinity assessment in Property Part 1, ed. I.F. Fergus Maroochydore, Queensland, Management Planning: Pittsworth Airborne October 1985, pp. 296–297, Standing Committee Geophysical Survey, Project Report Series on Soil Conservation. QO95003, Department of Primary Industries, Talbot, R. (Bob), Roberts, Max, McMahon, C. (Ron) Queensland. & Shaw, Roger 1981, Irrigation quality of Lockyer Valley alluvia bores during the 1980 drought, Technical publication No. 5, Department of Biology, Queensland Agricultural College.
146 Appendixes — Salinity publications for further references Knowles-Jackson, Clive 1987, ‘The occurrence of Condamine—Miles seepage salting in the Oakey soil conservation district’, in Landscape, soil and water salinity, Dalal, Ram 1986, ‘Salinity trends in Brigalow Proceedings of the Brisbane Regional Salinity soils’, in Landscape, soil and water salinity, Workshop, Brisbane, May 1987, Conference and Proceedings of the Darling Downs Regional Workshop Series QC87003, pp. B1-1 to B1-4, Workshop, Toowoomba, March 1986, Conference Department of Primary Industries, Queensland. and Workshop Series QC86001, pp. B5-1 to B5-5, Department of Primary Industries, Queensland. Molloy (Daly), Jenny & McIntyre, Geoff 1986, ‘Soil and water salinity in the Dalby District’, in Landscape, Free, Dave 1986, ‘Irrigation development and soil and water salinity, Proceedings of the Darling groundwater salinity in the upper Condamine Downs Regional Workshop, Toowoomba, March River Catchment’, in Landscape, soil and water 1986, Conference and Workshop Series QC86001, salinity, Proceedings of the Darling Downs Regional pp. B2-1 to B2-3, Department of Primary Industries, Workshop, Toowoomba, March 1986, Conference Queensland. and Workshop Series QC86001, pp. B12-1 to B12-6, Department of Primary Industries, Queensland. Stallman, Adrian 1992, Irrigation as a land management option for a salt-affected catchment, Orange, Denis & Smith, George 1986, ‘A case study Natural Resource Management Unit, Department of of salinity: Effect on a Brigalow grey clay at Primary Industries, Queensland, (poster paper). Drillham’, in Landscape, soil and water salinity, Proceedings of the Darling Downs Regional Thorburn, Peter 1991, ‘Occurrence and management of Workshop, Toowoomba, March 1986, Conference dryland salting on the Darling Downs, Queensland’, and Workshop Series QC86001, pp. B6-1 to B6-5, Australian Journal of Soil and Water Conservation, Department of Primary Industries, Queensland. 4:26–32. Shaw, Roger, Gardner, E. (Ted), Brebber, Lindsay, Thorburn, Peter 1989, ‘Dryland salinity on the Gordon, Ian, Thorburn, Peter & Littleboy, Mark Darling Downs’, Queensland Agricultural Journal, 1989, Current approaches to estimating and 115:217–224. predicting groundwater recharge in Queensland Thorburn, Peter, Geritz, Alan & Shaw, Roger 1986, with reference to the Darling Basin, Presented to ‘Causes and managements of dryland salting: A the Murray Darling Basin Commission Recharge case study’, in Landscape, soil and water salinity, Workshop, Melbourne, November 1989. Proceedings of the Darling Downs Regional Workshop, Toowoomba, March 1986, Conference and Workshop Series QC86001, pp. B9-1 to B9-16, South Burnett—Kingaroy Department of Primary Industries, Queensland. Dickenson, John & Kent, David 1989, Seepage and West, Dave, Geritz, Alan & Thorburn, Peter 1987, salty outbreaks in red soil areas around Kingaroy, ‘Revegetation of a dryland salting outbreak: a Farm Note SC8901003, Soil Conservation Services progress report’, in Landscape, soil and water Branch/Land Resources Branch, Department of salinity, Proceedings of the Brisbane Regional Primary Industries, Queensland. Salinity Workshop, Brisbane, May 1987, Conference Kent, David, 1986, ‘Salinity in the south Burnett’, in and Workshop Series QC87003, pp. B5-1 to B5-10, Landscape, soil and water salinity, Proceedings Department of Primary Industries, Queensland. of the Darling Downs Regional Workshop, West, Dave 1986, ‘Tree planting on the Darling Toowoomba, March 1986, Conference and Downs’, in Landscape, soil and water salinity, Workshop Series QC86001, pp. B1-1 to B1-3. Proceedings of the Darling Downs Regional Department of Primary Industries, Queensland. Workshop, Toowoomba, March 1986, Conference Reid, Bob, Shaw, Roger & Baker, Dennis 1979, Soils and Workshop Series QC86001, pp. B7-1 to B7-5, and irrigation potential of the alluvial flats of the Department of Primary Industries, Queensland. Byee Area, Barambah Creek, Murgon, Queensland, Agricultural Chemistry Branch Technical Report No. Pumicestone Passage 14, Department of Primary Industries, Queensland. Shaw, Roger 1978, Suitability of a low lying coastal area for small crop farming and suggested drainage and reclamation measures required, Final Report, Department of Primary Industries, Queensland.
Appendixes — Salinity publications for further references 147 Maryborough Glanville, Trevor & Leverington, Andrea 1987, ‘The reclamation of a saline area at the Woongarra Brown, M. D. & Simpson, John 1987, ‘Salinity and balancing storage, Bundaberg’, in Landscape, soil forestry in the Maryborough region’, in Landscape, and water salinity, Proceedings of the Bundaberg soil and water salinity, Proceedings of the Regional Salinity Workshop, Bundaberg, April 1987, Bundaberg Regional Salinity Workshop, Bundaberg, Conference and Workshop Series QC87001, pp. April 1987, Conference and Workshop Series B10-1 to B10-7, Department of Primary Industries, QC87001, pp. B7-1 to B7-3, Department of Primary Queensland. Industries, Queensland. Kingston, Graham 1993, Geo-hydrology of soil and Collings, A. (Steve) 1987, ‘Effect of Caribbean pine water salinity in the Maryborough Basin, thesis plantation establishment on water table levels submitted for PhD in Environmental Management, at Wongi, Queensland’, in Landscape, soil and Griffith University. water salinity, Proceedings of the Bundaberg Kingston, Graham 1987, ‘Application of Regional Salinity Workshop, Bundaberg, April 1987, electromagnetic induction instruments to Conference and Workshop Series QC87001, pp. investigation of soil salinity’, in Landscape, soil B6-1 to B6-9, Department of Primary Industries, and water salinity, Proceedings of the Bundaberg Queensland. Regional Salinity Workshop, Bundaberg, April 1987, Hughes, Keith 1987, ‘Assessment of salinity hazards Conference and Workshop Series QC87001, pp. in vacant Crown lands in the Maryborough area’, B4-1 to B4-13, Department of Primary Industries, in Landscape, soil and water salinity, Proceedings Queensland. of the Bundaberg Regional Salinity Workshop, Kingston, Graham 1985, ‘Soil salinity a hazard to Bundaberg, April 1987, Conference and Workshop productivity in southern areas’, BSES Bulletin, Series QC87001, pp. B3-1 to B3-16, Department of 12:14–17. Primary Industries, Queensland. Macnish, Stuart 1985, ‘The Port Curtis–Wide Bay Rolfe, Dennis 1987, ‘Seepage salting in Wongi State Land Resource Survey—salinity and land use Forest’, in Landscape, soil and water salinity, aspects’, in Landscape, soil and water salinity, Proceedings of the Bundaberg Regional Salinity Proceedings of the Rockhampton Regional Workshop, Bundaberg, April 1987, Conference Workshop, Rockhampton, May 1985, Conference and Workshop Series QC87001, pp. B5-1 to B5-4. and Workshop Series QC85002, pp. C2-1 to C2-3, Department of Primary Industries, Queensland. Department of Primary Industries, Queensland. Smith, Geoff 1987, ‘An overview of salinity in the Bundaberg upper and central Burnett and recent developments Cantor, John 1987, ‘A methodology for maintenance or in the south Burnett’, in Landscape, soil and water restoration of water quality in small farm storages’, salinity, Proceedings of the Bundaberg Regional in Landscape, soil and water salinity, Proceedings Salinity Workshop, Bundaberg, April 1987, of the Bundaberg Regional Salinity Workshop, Conference and Workshop Series QC87001, pp. Bundaberg, April 1987, Conference and Workshop B13-1 to B13-7, Department of Primary Industries, Series QC87001, pp. B9-1 to B9-12, Department of Queensland. Primary Industries, Queensland. Sunners, Frank 1993, Nitrate contamination—a study Forster, Bruce & Macnish, Stuart 1987, ‘Field of Bundaberg’s groundwater, thesis for Master of evaluation of the suitability for irrigation of Natural Resources, University of New England. caneland in the Isis mill area with particular emphasis on salinity and drainage hazard’, in Landscape, soil and water salinity, Proceedings Gladstone of the Bundaberg Regional Salinity Workshop, Plenderleigh, Rob & Hartigan, Roger 1987, ‘Vegetative Bundaberg, April 1987, Conference and Workshop colonisation of saline coal ash at Gladstone, Series QC87001, pp. B2-1 to B2-10, Department of central Queensland’, in Landscape, soil and water Primary Industries, Queensland. salinity, Proceedings of the Brisbane Regional Salinity Workshop, Brisbane, May 1987, Conference and Workshop Series QC87003, pp. B2-1 to B2-4, Department of Primary Industries, Queensland.
148 Appendixes — Salinity publications for further references Callide—Biloela—Moura Standley, John & Cowie, Bruce 1985, ‘Studies on an area of dryland salting near Thangool, central Dowling, A. (Tony) & Gardner, E. (Ted) 1988, ‘Spatial Queensland; Part 2—Establishment of trees in variation in salinity of some alluvial aquifers in the saline area’, in Landscape, soil and water central Queensland—a steady state analysis’, salinity, Proceedings of the Rockhampton Regional Australian Journal of Soil Research, 26:583–593. Workshop, Rockhampton, May 1985, Conference Dowling, A. (Tony) & Gardner, E. (Ted) 1985, ‘Alluvial and Workshop Series QC85002, pp. C6-6 to C6-11, groundwater salinity in the Callide Valley, central Department of Primary Industries, Queensland. Queensland’, in Landscape, soil and water Standley, John & Cowie, Bruce 1985, ‘Studies salinity, Proceedings of the Rockhampton Regional on an area of dryland salting near Thangool, Workshop, Rockhampton, May 1985, Conference central Queensland; Part 1—Description and and Workshop Series QC85002, pp. D1-1 to D1-8, drainage’, in Landscape, soil and water salinity, Department of Primary Industries, Queensland. Proceedings of the Rockhampton Regional Lawrence, Peter, Thorburn, Peter & Littleboy, Mark Workshop, Rockhampton, May 1985, Conference 1991, ‘Changes in surface and subsurface hydrology and Workshop Series QC85002, pp. C6-1 to C6-5, after clearing brigalow (Acacia harpophylla) Department of Primary Industries, Queensland. forest in a semi-arid climate: Measurements and modelling’, in International Hydrology and Water Resources Symposium 1991, Perth 2–4 October Dee and Don River Valleys 1991, Preprints vol. 2, pp. 374–380, The Institution Lloyd, John & Murphy, Greg 1985, ‘Irrigation salinity in of Engineers, Australia, National Conference the Dee and Don River Valleys’, in Landscape, soil Publication No. 91/22. and water salinity, Proceedings of the Rockhampton Standley, John 1989, Reclamation studies on an Regional Workshop, Rockhampton, May 1985, area of dryland salting near Thangool, central Conference and Workshop Series QC85002, pp. Queensland, Bulletin Series QB89006, Agricultural D2-1 to D2-4, Department of Primary Industries, Chemistry Branch, Department of Primary Queensland. Industries, Queensland. Thorburn, Peter, Cowie, Bruce & Hunter, Heather Standley, John, Cowie, Bruce & Larsen, Arnie 1987, 1985, ‘Salinity in irrigated soils of the Wowan area, ‘Studies on an area of dryland salting near Dee River Valley’, in Landscape, soil and water Thangool, central Queensland; Part 5—Survival of salinity, Proceedings of the Rockhampton Regional trees, 1984–1987’, in Landscape, soil and water Workshop, Rockhampton, May 1985, Conference salinity, Proceedings of the Brisbane Regional and Workshop Series QC85002, pp. D3-1 to D3-9, Salinity Workshop, Brisbane, May 1987, Conference Department of Primary Industries, Queensland. and Workshop Series QC87003, pp. B4-1 to B4-18, Department of Primary Industries, Queensland. Standley, John, Cowie, Bruce & Larsen, Arnie 1987, Rockhampton ‘Studies on an area of dryland salting near Chapman, David 1985, ‘Dryland salting at Tanby (field Thangool, central Queensland; Part 4—Drainage site)’, field notes accompanying Landscape, soil and salinity in the tree study area’, in Landscape, and water salinity, Proceedings of the Rockhampton soil and water salinity, Proceedings of the Brisbane Regional Workshop, Rockhampton, May 1985, Regional Salinity Workshop, Brisbane, May 1987, Conference and Workshop Series QC85002, Conference and Workshop Series QC87003, pp. Department of Primary Industries, Queensland. B3-1 to B3-10, Department of Primary Industries, Cummins, Vic 1985, ‘Dryland salting in Granodiorites Queensland. (field site)’, field notes accompanying Landscape, Standley, John & Cowie, Bruce 1985, ‘Studies on soil and water salinity, Proceedings of the an area of dryland salting near Thangool, central Rockhampton Regional Workshop, Rockhampton, Queensland; Part 3—Information from piezometer May 1985, Conference and Workshop Series records and water analyses’, in Landscape, soil and QC85002, Department of Primary Industries, water salinity, Proceedings of the Rockhampton Queensland. Regional Workshop, Rockhampton, May 1985, Hill, Clem 1994, ‘Ohio: Planting trees for feed’, Case Conference and Workshop Series QC85002, pp. study in Saltwatch Activity Book, Training Series C6-12 to C6-19, Department of Primary Industries, QE94003, Land Conservation, Department of Queensland. Primary Industries, Queensland, pp. 41–42.
Appendixes — Salinity publications for further references 149 Hughes, Keith 1985, ‘Dryland salting overview— Proserpine Rockhampton and Biloela’, in Landscape, soil and water salinity, Proceedings of the Rockhampton Gordon, Ian & Shaw, Roger 1992, The potential for Regional Workshop, Rockhampton, May 1985, development of salinity and watertable problems Conference and Workshop Series QC85002, pp. under irrigation in the Koolachu area, Proserpine, C1-1 to C1-5, Department of Primary Industries, consultancy report prepared for Water Resources. Queensland. Hughes, Keith 1985, ‘Dryland salting at Barmoya (field Bowen site)’, field notes accompanying Landscape, soil Maltby, John, Wright, Ross & McShane, Tom 1986, and water salinity, Proceedings of the Rockhampton ‘Quality of irrigation water in the Bowen area, Regional Workshop, Rockhampton, May 1985, north Queensland’, in Landscape, soil and water Conference and Workshop Series QC85002, salinity, Proceedings of the Burdekin Regional Department of Primary Industries, Queensland. Salinity Workshop, Ayr, April 1986, Conference Simpson, John 1985, ‘Salinity in forestry areas and Workshop Series QC86003, pp. B9-1 to B9-11, with particular reference to the Rockhampton Department of Primary Industries, Queensland. district’, in Landscape, soil and water salinity, Proceedings of the Rockhampton Regional Workshop, Rockhampton, May 1985, Conference Burdekin and Workshop Series QC85002, pp. C3-1 to C3-3, Ahern, Col, Shaw, Roger & Eldershaw, Val 1988, Department of Primary Industries, Queensland. Predicted deep drainage loss for Burdekin soils, in Interpretation by landscape units and agronomic groups, Part A, Publication QB88004, Department Emerald of Primary Industries, Queensland. Gardner, E. (Ted) 1979, The utility of plant Day, Ken & McShane, Tom 1986, ‘Predicting potential measurements in assessing the irrigation suitability toposequence salinisation—lower Burdekin’, in of cracking clay soils in the Emerald Irrigation Area, Landscape, soil and water salinity, Proceedings of final report on ACL–50. the Burdekin Regional Salinity Workshop, Ayr, April Gardner, E. (Ted) 1978, Techniques for evaluating 1986, Conference and Workshop Series QC86003, suitability for irrigation of cracking clay soils in pp. B5-1 to B5-12, Department of Primary Industries, the Emerald Irrigation Area, Master of Agricultural Queensland. Science Thesis, University of Queensland, Brisbane. Doherty, John 1989, Leichardt Downs electromagnetic Shaw, Roger & Gordon, Ian 1994, Salinity in cotton survey, ACTFR Report 89/09. areas, in Proceedings of the Seventh Australian Doherty, John 1988, 1989, 1990, Salt and water Cotton Conference, Gold Coast, August 1994. movement in hillslope soil toposequences in the Shaw, Roger & Yule, Don 1978, ‘Assessment of soils Burdekin River Irrigation Area, Progress reports, for irrigation, Emerald, Queensland’, Agricultural ACTFR Reports 88/09, 88/13, 89/01, 89/02, 89/08, Chemistry Branch Technical Report No. 13, 89/10, 90/4, Final report ACTFR Report 90/13. Department of Primary Industries, Queensland. Doherty, John 1987, Leichardt Downs resistivity survey, Shaw, Roger 1974, ‘Soil water relations of cracking ACTFR Report 87/01. clay soils in the Emerald Irrigation Area’, in Dowling, A. (Tony), Elliot, Peter, Ross, Peter & Proceedings of Central Queensland Soil Moisture Thorburn, Peter 1988, ‘Salt and water movement Workshop, pp. 36–41, Department of Primary in a furrow irrigated sodic duplex soil from the Industries, Queensland. Burdekin River Irrigation Area’, in Proceedings of the National Soils Conference, Canberra, May 1988, Mackay p. 241, Soil Science Society of Australia. Shaw, Roger, Gordon, Ian, Brebber, Lindsay Dowling, A. (Tony), Elliot, Peter, Thorburn, Peter, & Stallman, Adrian 1992, The potential for Ross, Peter & Hunt, Steve 1988, ‘Chloride and development of salinity and watertable problems water movement in a furrow irrigated sodic duplex affecting sustainable irrigation in the Pioneer Valley soil from the Burdekin River Irrigation Area’, in R. area, Mackay, consultancy report prepared for J. Smith and A. J. Rixon (eds), ‘Soil Management Water Resources, December 1992. 88’, Proceedings of a symposium, Toowoomba, September 1988, pp. 321–335, Darling Downs Institute of Advanced Education.
150 Appendixes — Salinity publications for further references Gardner, E. (Ted), Shaw, Roger, McShane, Tom & Shaw, Roger, Thorburn, Peter, McShane, Tom, Maltby, Brebber, Lindsay 1989, Leichhardt hydro-salinity John & Robson, Chris 1983, ‘The effectiveness of project, final report, submitted to Water Resources drainage in a region of variable aquifer hydraulic Commission, September 1989. conductivity in the Lower Burdekin region, north Gardner, E. (Ted) & Coughlan, Kep 1982, Physical Queensland’, in R.J. Smith and A.J. Rixon (eds), factors determining soil suitability for irrigated Proceedings of Symposium, Rural Drainage in crop production in the Burdekin-Elliot River area, Northern Australia, pp. 129–142, Darling Downs Technical Report No. 20, Agricultural Chemistry Institute of Advanced Education. Branch, Department of Primary Industries, Thorburn, Peter, Rose, Calvin, Shaw, Roger & Yule, Queensland. Don 1990, ‘Predictions of deep drainage below Maltby, John & McShane, Tom 1986, ‘Quality the root zone under irrigation from soil properties of underground water and related effects on and a simple salt balance model’, Proceedings, rice growth in the lower Burdekin area, north Management of Salinity in South-eastern Australia, Queensland’, in Landscape, soil and water Albury, September 1989, Australian Society of Soil salinity, Proceedings of the Burdekin Regional Science Incorporated, Riverina Branch. Salinity Workshop, Ayr, April 1986, Conference Williams, John, Bui, Elizabeth, Gardner, E. (Ted), and Workshop Series QC86003, pp. B3-1 to B3-6, Littleboy, Mark & Probert, Merv 1997, ‘Tree clearing Department of Primary Industries, Queensland. and dryland salinity hazard in the upper Burdekin McClurg, Jim, Ahern, Col & Donnollan, Terry 1986, catchment of north Queensland’, Australian Journal ‘Characteristics of inherently saline and sodic soils of Soil Research, 35:785–801. of the lower Burdekin’, in Landscape, soil and water salinity, Proceedings of the Burdekin Regional Salinity Workshop, Ayr, April 1986, Conference Collinsville and Workshop Series QC86003, pp. B7-1 to B7-12, Thompson, W. (Bill), Cannon, Mike, Shaw, Roger & Department of Primary Industries, Queensland. Clem, R. (Bob) 1982, Soils and special land use McShane, Tom 1986, ‘A review of salinity in the assessment of a mining lease area, Collinsville, Burdekin’, in Landscape, soil and water salinity, North Queensland, Agricultural Chemistry Branch Proceedings of the Burdekin Regional Salinity Technical Report No. 19, Department of Primary Workshop, Ayr, April 1986, Conference and Industries, Queensland. Workshop Series QC86003, pp. B1-1 to B1-8, Department of Primary Industries, Queensland. Ingham Shaw, Roger 1989, ‘Predicted deep drainage loss Wilson, Peter 1986, ‘Hydrology and sodicity of the under dryland and irrigation managements soloths, solodic soils and solodised solonetz soils for Burdekin soils’, in G.E. Rayment and V.E. in the Ingham area’, in Landscape, soil and water Eldershaw, Soils of the Burdekin River Irrigation salinity, Proceedings of the Burdekin Regional Area, Workshop Proceedings, Ayr, QC89003 Salinity Workshop, Ayr, April 1986, Conference pp. 37–48, Department of Primary Industries, and Workshop Series QC86003, pp. B6-1 to B6-5, Queensland. Department of Primary Industries, Queensland. Shaw, Roger 1986, ‘Predicted hydrology, salinity and sodicity changes under irrigation development in the lower Burdekin right bank’, in Landscape, soil Northern tablelands and water salinity, Proceedings of the Burdekin Grundy, Mike 1986, ‘Salinity in the Tablelands and Regional Salinity Workshop, Ayr, April 1986, northern semi-arid tropics’, in Landscape, soil and Conference and Workshop Series QC86003, pp. water salinity, Proceedings of the Burdekin Regional B8-1 to B8-16, Department of Primary Industries, Salinity Workshop, Ayr, April 1986, Conference and Queensland. Workshop Series QC86003, p. B2-1, Department of Shaw, Roger, Eldershaw, Val, Thompson, W. (Bill) Primary Industries, Queensland. & Smith, George 1984, Hydrology and salinity changes under irrigation—Lower Burdekin right bank (Fort site), Bulletin QB84004, Department of Primary Industries, Queensland.
Appendixes — Salinity publications for further references 151 References
ANZECC (Australian and New Zealand Environment Bird, P.R., Bicknell, D., Bulman, P.A., Buke, S.J.A., and Conservation Council), 1992, Australian Water Leys, J.F., Parker, J.N. & Voller, P. 1991, ‘The Quality Guidelines for fresh and marine waters, role of shelter in Australia for protecting soils, November 1992. plants and livestock’, in The role of trees in Arora, H.S. & Coleman, N.T. 1979, ‘The influence of sustainable agriculture—A national conference, electrolyte concentration on flocculation of clay 30 September–3 October 1991, Albury Convention suspensions’, Soil Science, 127:134–139. Centre, National Agroforestry Working Group. Arslan, A. & Dutt, G.R. 1993, ‘Solubility of gypsum Bolt, G.H. 1979, Soil Chemistry B. Physico-chemical and its prediction in aqueous solutions of mixed models, Elsevier Scientific Publishing Company, electrolytes’, Soil Science, 155:37–47. Amsterdam. Australian Bureau of Statistics 1993, Year Book Bouma, J. 1983, ‘Use of soil survey data to Australia 1994, Number 67, Australian Bureau of select measurement techniques for hydraulic Statistics, Canberra. conductivity’, Agricultural Water Management, 6:177–190. Australian Water Resources Council 1976, Review of Australia’s Water Resources 1975, Australian Bouwer, H. & Rice, R.C. 1976, ‘A slug test for Government Publishing Service, Canberra. determining hydraulic conductivity of unconfined aquifers with completely or partially penetrating Ayers, R.S. 1977, ‘Quality of water for irrigation’, wells’, Water Resources Research, 12:423–428. Journal of the Irrigation and Drainage Division, American Society Civil Engineers, 103(No. Bowler, J. 1990, ‘The last 500,000 years’, in The IR2):135–154. Murray, eds N. Mackay & D. Eastburn, Chapter 6, pp. 94–109, Murray Darling Basin Commission, Ayers, R.S. & Westcot, D.W. 1985, Water quality for Canberra. agriculture, FAO Irrigation and Drainage Paper No. 29 (Rev 1), Food and Agriculture Organisation of the Bresler, E., McNeal, B.L. & Carter, D.L. 1982, Saline United Nations, Rome. and sodic soils, principles—dynamics—modelling, Springer Verlag, Berlin. Ayers, R.S. & Westcot, D.W. 1976, Water quality for agriculture, FAO Irrigation and Drainage Paper No. Bruce, R.C. & Rayment, G.E. 1982, Analytical methods 29, Food and Agriculture Organisation of the United and interpretations used by the Agricultural Nations, Rome. Chemistry Branch for soil and land use surveys, Bulletin QB82004, Department of Primary Barrett-Lennard E.G. 1993, ‘Maximising production of Industries, Queensland. Atriplex species’, in Productive use of saline land, eds N. Davidson & R. Galloway, ACIAR Proceedings Cass, A. 1980, ‘Use of environmental data in No. 42, pp. 90–93. assessing the quality of irrigation water’, Soil Science, 129:45–53. Beckmann, G.G. 1983, ‘Development of old landscapes and soils’, in Soils an Australian Cass, A. & Sumner, M.E. 1982, ‘Soil pore structural Viewpoint, Chapter 4, pages 52–72, Division of stability and irrigation water quality: III, Evaluation Soils, CSIRO, Melbourne/ Academic Press, London. of soil stability and crop yield in relation to salinity and sodicity’, Soil Science Society of America Berkman, D.A. 1989, Field Geologists’ Manual, Journal, 46:513–517. 3rd edn, Australasian Institute of Mining and Metallurgy, Parkville, Victoria. Christiansen, I.H. 1993, Distribution and growth of plants in relation to soil salinity in south-east Bernstein, L. 1967, ‘Quantitative assessment of Queensland, BSc (Honours) thesis, Department of irrigation water quality’, American Society for Botany, University of Queensland, St Lucia. Testing Material Special Technical Publication, 416:51–65. Conacher, A.J. 1975, ‘Throughflow as a mechanism responsible for excessive soil salinization in non- Bernstein, L. & Francois, L.E. 1973, ‘Leaching irrigated, previously arable lands in the Western requirement studies: sensitivity of alfalfa to Australian wheatbelt: field study,’ Catena, 2:31–68. irrigation and drainage waters’, Soil Science of America Proceedings, 37:931–943.
152 References Daly, J.J. 1984,‘Cattle need shade trees’, Queensland Geritz, A.F. 1985, ‘The installation of piezometers and Agricultural Journal, 110(1):21–24. open wells for salinity investigations’, in Principles Department of Primary Industries 1994, Saltwatch of Landscape, Soil and Water Salinity, Proceedings Instruction Book, Training Series QE94004, of the Lockyer–Moreton Salinity Workshop, Department of Primary Industries, Brisbane. Ipswich, June 1985, pp. C4-1 to C4-6, Conference and Workshop Series QC 85004, Department of Devitt, D., Jarrell, W.M., Jury, W.A., Lunt, O.R. & Stolzy, Primary Industries, Queensland. L.H. 1984, ‘Wheat response to sodium uptake under zonal saline–sodic conditions, Soil Science Society Gill, J.Y. 1986a, Water quality for agriculture in of America Journal, 48:86–92. Queensland, Bulletin QB86004, Department of Primary Industries, Brisbane. Doneen, L.D. 1975, ‘Water quality for irrigated agriculture’, in Plants in Saline Environments, eds Gill, J.Y. 1986b, Agricultural water quality assessment, A. Poljakoff-Mayber & J. Gale, Springer–Verlag, Information Series QI86018, Department of Primary Berlin. Industries, Queensland. Dowling, A. & Gardner, E. 1988, ‘Spatial variation Gordon, I.J. (ed.) 1991, A survey of dryland and in salinity of some alluvial aquifers in central irrigation salinity in Queensland, Information Queensland—a steady state analysis’, Australian Series QI91034, Department of Primary Industries, Journal of Soil Research, 26:583–593. Queensland. Emerson, W.W. 1968, ‘The dispersion of clay from soil Grainger, G. 1995, Shallow sub-surface water: Is it a aggregates’, Transactions of the Ninth International viable irrigation supply?, WaterNote, Department of Congress of Soil Science, 1:617–626. Primary Industries, Queensland. Emerson, W.W. & Bakker, A.C. 1973, ‘The comparative Grayson, R.B. & Doolan, J.M. 1995, Adaptive effects of exchangeable calcium and magnesium Environmental Assessment and Management and sodium on some physical properties of red- (AEAM) and Integrated Catchment Management, brown earth subsoil’, Australian Journal of Soil Occasional Paper No. 1/95, Land and Water Research, 7:151–157. Resources Research and Development Corporation, Canberra. Evans, R., Brown, C. & Kellett, J. 1990, ‘Geology and groundwater’, in The Murray, eds N. Mackay and Greenway, H. & Munns, R. 1980, ‘Mechanisms of salt D. Eastburn, Murray Darling Basin Commission, tolerance in non-halophytes’, Annual Review Plant Canberra, pp. 77–93. Physiology, 31:149–190. Feigin, A. 1985, ‘Fertilisation management of crops Habermehl, M.A. 1980, ‘The Great Artesian Basin’, irrigated with saline water’, Plant and Soil, BMR Journal of Australian Geology and Geophysics, 89:289–299. 5:9–38. Fisher, M.J. & Skerman, P.J. 1986, ‘Salt tolerant forage Ham G.J., McMahon G.G., Elliot P.J. & Smettem plants for summer rainfall areas’, Reclamation and K.R.J. 1993, ‘Cropping sodic soils in the Burdekin Revegetation Research, 5:263–284. River Irrigation Area’, in Australian sodic soils: Distribution, properties and management, eds R. Freeze, R.A. & Cherry, J.A. 1979, Groundwater, Prentice Naidu, M.E. Sumner & P. Rengasamy pp. 139–146, Hall Inc., New Jersey. CSIRO, Australia. Gardner, E.A. 1985a, ‘Hydro-salinity problems in the Hardie, L.A. & Eugster, H.P. 1970, ‘The evolution of Lockyer Valley—real and perceived’, in Landscape, closed basin brines’, Mineral Society of America soil and water salinity, Proceedings of the Lockyer– Special Paper, 3:273–290. Moreton Regional Workshop, Ipswich, June 1985, Conference and Workshop Series QC85004, pp. Hart, B.T. 1974, A compilation of Australian water D1-1 to D1-9, Department of Primary Industries, quality criteria, Australian Water Research Council Queensland. Technical Paper No. 7, Australian Government Publishing Service, Canberra. Gardner, E.A. 1985b, ‘Soil water’, in Identification of soils and interpretation of soil data: Refresher Heuer, B. Meiri, A. & Shalhevet, J. 1986, ‘Salt tolerance course in soil science, Australian Society of Soil of egg plant’, Plant and Soil, 95:9–13. Science Inc. (Queensland Branch), Brisbane, pp. Hinchley, D. 1994, Trees for dryland salinity control 197–234. in Queensland: Guidelines for landowners and extension officers, Project Report 691/2 for Master of Natural Resources, University of New England, Armidale.
References 153 Hoffman, G.J. & van Genutchen, M.Th. 1983, Marcar, N.E., Hussain, R.W., Arunin, S. & Beetson, ‘Soil properties for efficient water use: water T. 1991, ‘Trials with Australian and other Acacia management for salinity control’, in Limitations species on salt-affected land in Pakistan, Thailand to efficient water use in crop production, eds H.M. and Australia’, ACIAR Proceedings, 35:229–232. Taylor, W.R. Jordan & T.R. Sinclair, ASAI, CSSAI and Marion, G.M. & Babcock, K.L. 1976, ‘Predicting specific SSSAI, Madison, Wisconsin pp. 73–85. conductance and salt concentration in dilute Hughes, K.K. 1982a, Summary report on salinity aqueous solutions’, Soil Science, 122:181–187. in the Kalbar Area, unpublished internal report, McDonald, R.C. & Isbell, R.F. 1990, ‘Soil profile’, in Division of Land Utilisation, Department of Primary Australian Soil and Land Survey, Field Handbook, Industries, Queensland. eds R.C. McDonald, R.F. Isbell, J.G. Speight, J. Hughes, K.K. 1982b, ‘Causes, effects and potential for Walker & M.S. Hopkins, Inkata Press, Melbourne, salinity in the future’, in Proceedings 23rd Annual 2nd edn, pp. 103–152. AAAF Conference, Land Degradation, ed. J.R. Fisher, McIntyre, D.S. 1980, ‘Basic relationships for salinity Brisbane. evaluation from measurements on soil solution’, Hughes, K.K. 1979, Assessment of dryland salinity Australian Journal of Soil Science, 18:199–206. in Queensland, Division of Land Utilisation Miyamoto, S. 1980, ‘Effects of bicarbonate on sodium Report 79/7, Department of Primary Industries, hazard of irrigation water: alternative formulation’, Queensland. Soil Science Society of America Journal, Isbell, R.F., Reeve, R. & Hutton J.T. 1983, ‘Salt and 44:1079–1084. sodicity’, in Soils an Australian Viewpoint, Division Miyamoto, S. 1979, ‘Fundamentals of soil of Soils, CSIRO, Melbourne/Academic Press, management: recent developments and London, pp. 107–117. challenges’, in Proceedings of the Inter-American Jacobsen, T. & Adams, R.M. 1958, ‘Salt and silt in Conference on Salinity and Water Management, pp. ancient Mesopotamian Agriculture’, Science, 181–202. 128:1251–1258. Morris, J.D. & Thompson, L.A.J. 1983, ‘The role of trees Kingston, G. 1985, ‘Soil salinity a hazard to in dryland salinity control’, Proceedings of the Royal productivity in southern areas,’ BSES Bulletin, Society of Victoria, 95(3):123–131. 12:14–17. Mott, J.J. & McComb, A.J. 1974, ‘Patterns in annual Maas, E.V. 1986, ‘Salt tolerance of plants’, Applied vegetation and soil microenvironments in Agricultural Research, 1:12–25. Australian rangelands’, in Plant morphogenesis for Maas, E.V. 1985, ‘Crop tolerance to saline sprinkling scientific management of range resources, USDA water’, Plant and Soil, 89:273–284. Miscellaneous Publication 1271, Washington D.C., pp. 167–185. Maas, E.V. & Hoffman, G.J. 1977, ‘Crop salt tolerance— current assessment,’ Journal of the Irrigation and Murray–Darling Basin Commission 1993, Dryland Drainage Division, Proceedings of the American Salinity Management in the Murray–Darling Basin, Society of Civil Engineers, 103:115–130. prepared for the Murray–Darling Basin Ministerial Council by the Dryland Salinity Management Macumber, P.G. 1978, ‘Hydrologic change in the Working Group. Loddon Basin: The influence of groundwater dynamics on surface processes’, Royal Society of Northcote, K.H. & Skene, J.K.M. 1972, Australian Victoria, Proceedings, 90:125–138. soils with saline and sodic properties, CSIRO Soil Publication No. 27, CSIRO Melbourne, Australia. Malcolm, C.V. & Allen, R.J. 1981, ‘The Mallen niche seeder for establishment on difficult sites’, The Olsen, R.E. & Mesri, G. 1970, ‘Mechanisms controlling Australian Rangeland Journal, 3:106–109. compressibility of clay’, Journal of the Soil Mechanics and Foundations Division, Proceedings Malcolm, C.V. & Cooper, G.J. 1974, ‘Samphire for of the American Society of Civil Engineers, waterlogged saltland’, Journal of Agriculture 96:1863–1978. (Western Australia), 27(2):59–63. (Also published as Western Australia Department of Agriculture Oster, J.D. & Schroer, F.W. 1979, ‘Infiltration as Farmnote 56/88.) influenced by irrigation water quality’, Soil Science Society of America Journal, 43:444–447. Marcar, N.E., Crawford, D.F. & Leppert, P.M. 1993, ‘The potential of trees for utilisation and management of Peck, A.J. 1978, ‘Salinization of non-irrigated soils and salt-affected land’, Australian Centre for associated streams: A review’, Australian Journal of International Agricultural Research Proceedings, Soil Research, 16:157–168. 142:17–22.
154 References Piper, A.M. 1944, ‘A graphical procedure in the Schofield, N.J. 1991, ‘Tree planting for dryland geochemical interpretation of water analyses’, salinity control in Australia’, in The role of trees in Transactions American Geophysical Union, sustainable agriculture—A national conference, 25:914–923. 30 September–3 October 1991, Albury Convention Powell, B. 1985, ‘Morphological indicators of soil Centre, National Agroforestry Working Group. wetness’, in Principles of Landscape, Soil and Shainberg, I., Oster, J.D. & Wood, J.D. 1980, Sodium/ Water Salinity, Proceedings of the Lockyer–Moreton calcium exchange in montmorillonite and illite regional workshop, Ipswich, June 1985, pp. C3-1 to suspensions, Soil Science Society of America C3-7, Conference and Workshop Series QC85004, Journal, 44:960–964. Department of Primary Industries, Queensland. Shaw, R.J. 1996, A unified soil property and sodicity Queensland Forest Service 1991, Trees and shrubs, model of salt leaching and water movement, PhD Department of Primary Industries, Queensland. thesis, University of Queensland. Quirk, J.P. & Murray, R.S 1991, Towards a model for Shaw, R.J. 1994, Estimation of the electrical soil structural behaviour, Australian Journal of Soil conductivity of saturation extracts from the electrical Research, 29:829–867. conductivity of 1:5 soil:water suspensions and Rayment, G.E. & Higginson, F.R. 1992, Australian various soil properties, Project Report QO94025, Laboratory Handbook of Soil and Water Chemical Department of Primary Industries, Queensland. Methods, Inkata Press, Melbourne. Shaw, R.J. 1993, ‘Guidelines for decision making on Rengasamy, P. & Olsson, K.A. 1991, ‘Sodicity and utilisation of salt affected soils in summer rainfall soil structure’, Australian Journal of Soil Research, areas’, in Proceedings of the National Conference 29:935–952. on Land Management for Dryland Salinity Control, Bendigo, pp. 89–97. Rhoades, J.D. 1983, ‘Using saline waters for irrigation’, International Workshop on Salt-affected Soils of Shaw, R.J. 1988, ‘Soil salinity and sodicity’, in Latin America, October, 1983, Venezuela. Understanding Soils and Soil Data, ed. I.F. Fergus, Australian Society of Soil Science Incorporated, Rhoades, J.D. 1982, ‘Reclamation and management of Queensland Branch, Brisbane. p. 109. salt afflicted soils after drainage’, in Proceedings of the First Annual Western Provincial Conference, Shaw, R.J. 1987, Towards a quantitative irrigation Rationalization of Water and Soil Research water quality assessment model for Australia, a Management, pp. 123–197. report of studies during a 1984 Churchill Fellowship in Israel and USA, report to the Winston Churchill Rhoades, J.D. 1977, ‘Potential for using saline Memorial Trust. agricultural drainage waters for irrigation’, Proceedings, Water Management for Irrigation and Shaw, R.J., Brebber L., Ahern C. & Weinand M. 1994, Drainage, ASCE, Reno, Nevada, 20–22 July 1977, ‘A review of sodicity and sodic soil behaviour in pp. 85–116. Queensland’, Australian Journal of Soil Research, 32:143–172. Roberts, G. 1984, Plotting a better future for lambs, Queensland Agricultural Journal, 110(1):25–26. Shaw, R.J. Eldershaw, V.J., Thompson, W.P. & Smith, G.D. 1984, Changes in hydrology and salinity Rose, C.W., Dayananda, P.W.A., Nielson, D.R. & under irrigation agriculture on the Fort Site, Lower Biggar, J.W. 1979, ‘Long-term solute dynamics and Burdekin Right Bank, North Queensland, Bulletin hydrology in irrigated slowly permeable soils’, QB84004, Department of Primary Industries, Irrigation Science, 1:77–87. Queensland. Runciman, H.V. 1986, ‘Forage production from salt Shaw, R.J. Hughes, K.K., Thorburn, P.J. & Dowling, affected wasteland in Australia’, Reclamation and A.J. 1987, ‘Principles of landscape, soil and water Revegetation Research, 5:17–29. salinity—processes and management options’, Part Russell, J.S. 1976, ‘Comparative salt tolerance of A in Landscape, soil and water salinity, Proceedings some tropical and temperate legumes and tropical of the Brisbane Regional Salinity Workshop, grasses’, Australian Journal of Experimental Brisbane, May 1987, Conference and Workshop Agriculture and Animal Husbandry, 16:103–109. Series QC87003, Department of Primary Industries, Scanlan, J.C. 1991, ‘Management of native woody Queensland. vegetation on farms in Queensland’, in The role Shaw, R.J. & Thorburn, P.J. 1985a, ‘Prediction of of trees in sustainable agriculture—A national leaching fraction from soil properties, irrigation conference, 30 September–3 October 1991, Albury water and rainfall’, Irrigation Science, 6:73–83. Convention Centre, National Agroforestry Working Group.
References 155 Shaw, R.J. & Thorburn, P.J. 1985b, ‘Towards a Thorburn, P.J. & Gardner, E.A. 1986, ‘Plant available quantitative assessment of water quality for water capacity of irrigated soils’, in Proceedings of irrigation’, in Fifth Afro Asian Regional Conference, Irrigation Management Workshop, eds W.H. Hazard, International Commission on Irrigation and R.J. Shaw & J.F. Bourne, Queensland Agricultural Drainage, Townsville, Queensland. College, Department of Primary Industries, Shaw, R.J. & Yule, D.F. 1978, Assessment of soils Queensland, pp. 19–32. for irrigation, Emerald, Queensland, Agricultural Thorburn, P.J., Geritz, A.F. & Shaw, R.J. 1986, ‘Causes Chemistry Branch Technical Report No. 13, and managements of dryland salting: A case study’, Department of Primary Industries, Queensland. in Landscape, soil and water salinity, proceedings Shockley, D.R. 1955, ‘Capacity of soil to hold of the Darling Downs Regional Salinity Workshop, moisture’, Agricultural Engineering, 36:109–112. Toowoomba, March 1986, pp. B9-1 to B9-19, Department of Primary Industries, Queensland. Skene, J.K.M. 1965, ‘The diagnosis of alkali soils’, The Journal of the Australian Institute of Agricultural Thorburn, P.J., Rose, C.W., Shaw, R.J. & Yule, D.F. 1987, Science, 31:321–322. ‘SODICS: A program to calculate solute dynamics in irrigated clay soils’, in Landscape, soil and water Smith, R.J. & Hancock N.H. 1986, ‘Leaching salinity, Proceedings of the Bundaberg Regional requirement of irrigated soils’, Agricultural Water Workshop, Bundaberg, April 1987, Conference and Management, 11:13–22. Workshop Series QC87001, pp. B12-1 to B12-9, Suarez, D.L. 1981, ‘Relation between pHC and sodium Department of Primary Industries, Queensland. adsorption ratio (SAR) and an alternative method Townson, T. & Roberts, M. 1992, Vegetation for saline of estimating SAR of soil or drainage waters’, Soil areas, Field Case Study Series, LWMA Inc., Gatton. Science Society of America Journal, 45:469–475. USSL (United States Salinity Laboratory) staff 1954, Syme, G.J., Butterworth, J.E. & Nancarrow, B.E. 1994, Diagnosis and improvement of saline and alkali National whole catchment management: A review soils, Agricultural Handbook No. 60, US Department and analysis of processes, Occasional Paper No. of Agriculture, US Government Printer, Washington. 1/94, Land and Water Research and Development Corporation, Canberra. van Olphen, H. 1977, An introduction to clay colloid chemistry, 2nd edn, John Wiley and Sons, New York. Talsma, T. 1963, The control of saline groundwater, Meded, Landbouwhogeschool, Wageningen, VIRASC (Victorian Irrigation Research and Advisory 63:1–68. Services Committee) 1980, Quality aspects of farm water supplies, 2nd edn, Victorian Irrigation Tanji, K.K. & Biggar, J.W. 1972, ‘Specific conductance Research and Advisory Services Committee, model for natural waters and soil solutions of Victoria. limited salinity levels’, Water Resources Research, 8:145–153. Voller, P.J. & Molloy, J.M. 1993, Points to consider before clearing land in south Queensland, Thompson, I.L., Barrett, J.R. & Jones. 1992, ‘Decision Information Series QI93017, Department of Primary Support Systems for US Agriculture—A Status Industries, Queensland. Report’, in Computers in Agricultural Extension Programs, eds D.G. Watson, F.S. Zazveta & A.B. Warren, B.E., Bunny, C.J. & Bryant L.B. 1990, ‘A Bottcher, ASAE Publication 1–92, ASAE, Michigan, preliminary examination of the nutritive value USA, pp. 670–675. of four saltbush (Atriplex) species’, Proceedings of the Australian Society of Animal Production, Thompson, W.P. 1977, Soils of the Lower Burdekin 18:424–427. River, Elliott River Area, North Queensland, Agricultural Chemistry Branch Technical Report No. Wells, C.B. 1978, Electrolytic conductivity of soil 10, Department of Primary Industries, Queensland. solution and water conversion from conductance measurements at field temperature, Division of Thorburn, P.J., Cowie, B.A. & Hunter, H.M. 1985, Soils Technical Paper No. 37, CSIRO, Melbourne. ‘Salinity in irrigated soils of the Wowan area, Dee River Valley’, in Landscape, soil and water salinity, West, D.W. & Francois, L.E. 1982, ‘Effects of salinity on Proceedings of the Rockhampton Regional Salinity germination growth and yield of cowpea’, Irrigation Workshop, May 1985, Rockhampton, Conference Science, 3:169–175. and Workshop Series QC85002, pp. D3-1 to D3-9, Wilcocks, J. & Young, P. 1991, Queensland’s rainfall Department of Primary Industries, Queensland. history: graphs of rainfall averages 1880–1988, Information Series QI91002, Department of Primary Industries, Queensland.
156 References Wilcox, D.G. 1979, ‘The contribution of the shrub component in arid pastures to production from sheep’, in Studies of the Australian Arid Zone IV. Chenopod shrublands, eds R.D. Graetz and K.M.W. Howes, Proceedings of a symposium held by the Rangelands Research Unit of the Division of Land Resources Management, Riverina Laboratories, Deniliquin, New South Wales, October 1975, CSIRO, Melbourne, pp. 170–177. Williams, J., Bui, E.N., Gardner, E.A., Littleboy, M. & Probert, M.E. 1997, ‘Tree clearing and dryland salinity hazard in the Upper Burdekin Catchment of North Queensland’, Australian Journal of Soil Research, 35:785–801. Wilson, A.D. & Graetz, R.D. 1980, ‘Cattle and sheep production on an Atriplex vesicaria (Saltbush) community’, Australian Journal of Agricultural Research, 31:369–378. Wilson, P.R. 1982, ‘The relationship between soil characteristics, water-table heights and sugar cane yields in the Macknade mill area’, in Proceedings of Symposium on Rural Drainage in Northern Australia,eds R.J. Smith & A.J. Rixon, Darling Downs Institute of Advanced Education, Toowoomba, pp. 53–66. Winks, W.R. 1963, Safe waters for stock, Division of Plant Industry Advisory Leaflet Number 753, Department of Primary Industries, Queensland. (Reprinted from Queensland Agricultural Journal, December 1963.) Working Party on Dryland Salinity in Australia 1982, Salting of non-irrigated land in Australia, Soil Conservation Authority, Victoria for the Standing Committee on Soil Conservation. Wreczycki, R.J. 1968, ‘Findings on boron content of Queensland waters’, Queensland Agricultural Journal, 94:331. Yaalon, D.H. 1983, ‘Climate, time and soil development’, in Pedogenesis and soil taxonomy. I. Concepts and interactions, eds L.P. Wilding, N.E. Smeck & G.F. Hall, Elsevier Science Publishers, Amsterdam, pp. 233–251. Yo, S.A. & Shaw, R.J. 1990, Salinity tolerance of various crops, Information Series QI900020, Department of Primary Industries, Queensland.
References 157 Useful conversions and relationships
EC1:5 and chloride1:5 conversions Common salts and ions:
To estimate the contribution of chloride to EC1:5 in a converting from mg/L to 1:5 soil:water suspension, assuming chloride is the mmole /L (meq/L) dominant ion, where ECCl is measured as dS/m: c To convert from divide by mg/L to mmole /L (equivalent weight) ECCl = 6.64 x %Cl (per weight of soil) . . . . . 38 c Ions Ca2+ 20.0 A more accurate measure of the contribution of K+ 39.1 chloride to EC1:5 (Shaw 1994) is given by: Mg2+ 12.2 Na+ 23.0 log ECCl = 0.92 log(56.42 x %Cl) – 0.865 . . . . 39 Cl– 35.5 2– Percentage chloride can be determined from other CO3 30.0 measures of chloride contribution as follows: 2– HCO3 61.0 – NO3 62.0 -4 2– %Cl = (mgCl / kg soil)* 10 ...... 40 SO4 48.0 Salts mmolecCL/100g soil %Cl = ...... 41 CaCO3 50.0 28.21 CaSO4 68.1 mmole CL/litre of soil extract %Cl = c ...... 42 NaCl 58.5 56.42 Na2CO3 53.0
NaHCO3 84.0
Note: mmolec/L and meq/L are identical units. mmolec/L is consistent SAR and ESP conversions with the SI unit convention. The subscript ‘c’ refers to unit charge and To convert the SAR of a soil solution or irrigation water accounts for differences caused by ion valency. to the expected soil ESP in equilibrium with that water (USSL 1954):
100(–0.0126 + 0.01475SAR) Converting units of concentration ESP = ...... 43 1 + (–0.0126 + 0.01475SAR) To convert from to multiply by grains/gallon (imperial) mg/L 14.25 This empirical equation satisfies the theoretical grains/gallon NaCl mg Cl/L 8.66 boundary condition for high SAR and ESP values. parts/100 000 mg/L 10 However, the original data used in the derivation of normality mmolec/L 1 000 this relationship were SAR < 65 and ESP < 50. meq/L mmolec/L 1
The reverse regressed relationship for the USSL (1954) mmolec/L meq/L 1 data, which should not be applied for ESP > 50, is: mmolec/L mg/L equivalent weight (table above) 1.128 SAR = 0.6906 ESP ...... 44 mmolec/L mmole/L valency (R2 = 0.888) mg/L tons of salt 0.00136 per acre foot The 95% confidence limits on the coefficients are: mg/L tonnes of salt 1.001 a 0.340–1.041 per ML (where b 0.986–1.270. 1 ML = 1 hectare x 100 mm depth)
158 Useful conversions and relationships Converting between EC units and approximate TDI values
If you multiply by the numbers shown in the table to get these units have TDI mg/L mmolec/L grains/ these S/m dS/m mS/m mS/m mS/cm mS/cm (ppm) (meq/L) gallon units S/m 10 1 000 1 000 000 10 10 000 2/3 x 10 000 100 400 dS/m 0.1 100 100 000 1 1 000 2/3 x 1 000 10 40 mS/m 0.001 0.01 1 000 0.01 10 2/3 x 10 0.1 0.4 mS/m 10–6 10–5 0.001 10–5 0.01 2/3 x 0.01 10–4 4 000 mS/cm 0.1 1 100 100 000 1 000 2/3 x 1 000 10 40 mS/cm 10–4 0.001 0.1 100 0.001 2/3 0.01 0.04 TDI mg/L 1.5 x 10–4 0.0015 0.15 150 0.0015 1.5 0.015 0.06 (ppm) mmole /L c 0.01 0.1 10 10 000 0.1 100 2/3 x 100 4 (meq/L) grains/ gallon 0.002 0.02 2 2 000 0.02 20 14 0.02 (imperial)
Note: TDI conversions are working approximations only, suitable for quick calculations. More accurate methods for TDI conversions are provided in the table Converting from electrical conductivity (EC dS/m) to other measures of salinity page 159.
Converting from electrical conductivity EC (dS/m) to other measures of salinity
To convert EC (dS/m) to in the EC (dS/m) range multiply by/calculate Reference TDS mg/L1 0.1 to 5 640 USSL (1954) (strictly Total Dissolved Salts by concentration; approximates TDI) 0.2 to 0.6 620–740 0.6 to 6 600 VIRASC (1980) 6 to 30 600–690 TDS (calculated) mg/L1 < 2.4 550–950 Tanji & Biggar (1972) (equivalent to TDI) 730–780 (average) mmolec/L (meq/L)2 approx. 10 USSL (1954) 9.1–13.1 Tanji & Biggar (1972) log N = 0.955 + 1.039(log EC) Marion & Babcock (1976) where N is equivalent concetration (note following table for reverse calculations) Osmotic potential (bars) log osmotic potential = 1.111 McIntyre (1980) (log EC) – 0.512 % total soluble salts 0.336 (for 1:5 soil:water suspension)
Notes: 1. For definitions of TDI, TDS (calculated) and TDS (evaporation), refer to glossary entry for salinity. 2. Undissociated ions and ion pair formation result in proportionately lower EC with increasing concentration.
Useful conversions and relationships 159 Converting from equivalent concentration (mmolec/L) to EC (dS/m) To convert equivalent calculate Reference concentration (mmolec/L) to where N is equivalent concentration EC (dS/m) (mmolec/L): log EC = 0.960(log N) – 0.917 reverse of Marion & Babcock (1976) equation
log EC = 0.921(log N) – 0.865 McIntyre (1980)
Converting measures of soil Notes on gypsum volume and density • Fertiliser-grade gypsum is about 90% pure and contains 23% of calcium by weight. volume of pores • One mmolec/L of Ca from 100% gypsum = 86 kg Void ratio = 3 volume of solids gypsum dissolved in 1‑000 m of water, (that is, per ML). soil particle density = +1 • To replace exchangeable Na on soil clay exchange bulk density sites with Ca from gypsum (assuming full efficiency of exchange in Na replacement): for each cmole / 2 650 c = +1 kg of exchangeable Na (cmole /kg soil) in soil per bulk density (kg/m3) c hectare of 100 mm depth, use 1.375 tonnes of 100% pure gypsum.
bulk density For example, to reduce ESP from 6 to 3 in the surface Soil porosity = 1 – 100 mm of a soil would require 3 x 1.375 tonnes of soil particle density gypsum at 100% pure or 3 x 1.375/0.9 at 90% pure. Since it will not be fully utilised in ion exchange, the amount of gypsum should be increased by 1 000 (1 – air content as %) Soil porosity = 1 – approximately 1.5 for the soil surface and more for 1 000 + water content greater depths. A reasonable application per hectare soil particle density (kg/kg) of soil surface is 3 to 5 tonnes. (kg/m3) Figure 75. Soil is composed of solid particles of many different shapes and sizes interspersed with pore space For cracking clay soils and 5% air content at macimum containing varying mixtures of soil solution and air (Gardner field water content 1985). 950 3 Bulk desnity at Wmax(kg/m ) = 0.3774 + Wmax(kg/kg)
Figure 74. Schematic diagram of the soil as a three-phase system. M and V denote mass and volume while subscripts s, w, a, t and p refer to soil solids, water, air, total soil and porosity respectively (from Gardner 1985). air
volume relations solid mass relations Va gas Vp Ma Vw soil solution Vt Mw liquid Mt
Vs
Ms solid
160 Useful conversions and relationships Glossary
aquifer A permeable formation, group of formations, CCR Ratio of the CEC to clay content of a soil. Provides or part of a formation capable of storing and a surrogate measure of clay mineralogy and used transmitting sufficient quantities of water under to define co-efficients in the SALF model. Units are normal hydraulic gradients to cause changes in the molec/kg. As a guide: pressure head or watertable level in a short period. < 0.20 kaolinite An aquifer is confined if the upper and lower 0.20-0.35 kaolinite and illite boundaries to the saturated permeable material are essentially impervious. In an unconfined aquifer 0.35-0.55 mixed mineralogy partly filled with water, the watertable defines the 0.55-0.75 mixed mineralogy with a high upper water level. A perched aquifer, the upper proportion of montmorillonite surface of which is called a perched watertable, 0.75-0.95 dominantly montmorillonite is an unconfined groundwater body supported by > 0.95 montmorillonite plus feldspars a small impermeable or slowly permeable unit. In a semiconfined (or leaky) aquifer, the confining and/or layers are slowly permeable in a vertical direction. CEC from other than the clay fraction. In a semi-unconfined aquifer, the confining layers class A pan evaporation The evaporation of water from are sufficiently permeable for horizontal flow to a standard class A evaporation pan, expressed as occur in the confining layer in addition to vertical mm/d. water flow. clay minerals Secondary crystalline minerals base flow Flow of water in a stream or river derived produced by rock weathering. Clay minerals from groundwater seepage or throughflow into determine characteristic soil behaviour in terms the watercourse. Base flow varies from a minor of ion exchange, water holding, swelling and proportion of stream flow during high runoff periods shrinking, and soil texture. Clay minerals differ to a major proportion of stream flow during dry according to ion substitution in the silicate layer periods. lattice structure. The three most common types capillary fringe Portion of the saturated zone are the kaolinite group (two layer silicates with immediately above the watertable into which water low CEC), the illite group (three layer silicates with is drawn as a result of capillary action (movement low to moderate CEC) and the montmorillonite of soil moisture through fine soil as the result of (smectite) group (three layer silicates with high CEC surface tension forces between the water and that swell and shrink on wetting and drying). individual soil particles). In this zone, the porosity discharge area Area in the landscape where the net is saturated and the pressure head is less than movement of groundwater is out of the catchment. atmospheric. Waterlogging and salting are most likely to occur catchment Area of a landscape from which a surface in this area, as expressions of groundwater watercourse or groundwater system derives its discharging at the soil surface by seepage or water. Catchments are generally separated by ‘no evaporation. flow’ divides associated with high topography. dispersion Process whereby clay particles are repelled Cation Exchange Capacity (CEC) In the presence of by electrostatic forces and mechanical forces (such water, an amount of cations on the surface layers as swelling) and separate from each other, forming of clay minerals will be easily exchanged with other a suspension of clay particles in water. Dispersion cations when these are available in solution, hence is facilitated by high levels of exchangeable the term ‘exchangeable’ cations. Expressed in sodium, low salt content, and energy input (such millequivalents per 100 grams of dry clay. as raindrop impact, water flow, cultivation). (The converse process is flocculation.) drainable porosity Capacity of a soil to hold water between saturation point and the point where water ceases to drain readily from the soil (field capacity), usually expressed as depth (mm). dryland Not under irrigation.
Glossary 161 electrical conductivity (EC) See salinity. hydraulic head Height at which water stands in evapotranspiration Water lost as vapour from a a piezometer tube or tensiometer connected a vegetated area by direct evaporation of free water point in a particular subsurface layer, measured as well as transpiration of water by the vegetation. relative to a chosen elevation datum. Hydraulic The combined term is used because in practice it is head, expressed in metres, is the sum of three difficult to distinguish between the contributions of components: the elevation head, defined with these two paths of water loss. reference to the chosen datum (hz); the pressure head, defined with reference to atmospheric exchangeable sodium percentage (ESP) Commonly pressure (hp); and the velocity head (hv). Water used as a measure of soil sodicity, ESP is the invariably flows from points of higher hydraulic proportion of sodium adsorbed on the clay mineral head to points of lower head down the hydraulic surfaces as a proportion of total cation exchange gradient. See also potentiometric surface. capacity, expressed as a percentage. hydrology The study of water movement in various field capacity Soil water content at the point when states through the terrestrial and atmospheric water ceases to drain readily from the soil, environments, including underground water, expressed as weight/weight. Heavy clay soils do surface water and rainfall, embracing the concept not have a discrete point at which field capacity is of a hydrologic cycle. This study involves aspects achieved. of soils, geology, oceanography, and meteorology, flocculation Process whereby the attractive forces emphasising the processes and quantities of water between clay particles are greater than the flow above the terrestrial surface. repulsive forces, resulting in the formation of larger illite See clay minerals. aggregates of clay particles. (The converse process is dispersion.) intake area See recharge area. gleyed soil A soil developed under poor drainage irrigation water salting Salinity or sodicity in conditions, characterised by reduced (lack of irrigated soils due to an accumulation of salt or oxygen) conditions and the reduction of metal exchangeable sodium contributed by irrigation oxides to their metallic forms. Gleyed soils have a water. gley (greyish, bluish, or greenish coloured) mottle. kaolinite See clay minerals. groundwater Water occurring below the surface of the landform feature Identifiable part or feature of the landscape, at greater pressure than atmospheric, land surface that has characteristic form and occupying cavities and spaces in regolith and properties identifiable in the field. In relation to bedrock. The upper surface of the groundwater is salinity, a natural landform or artificial landscape the watertable. feature that controls water movement in such a groundwater discharge Removal of water from the way that portions of the landscape, called potential saturated zone. Water exits the groundwater by discharge areas, are at risk of salting if groundwater surface seepage, subsurface outflow, base flow in recharge exceeds groundwater outflow. streams, evaporation and evapotranspiration. leaching Removal of soluble materials in solution by groundwater recharge Water entering the groundwater water moving through a soil. from the saturated zone immediately above the macropores Naturally occurring continuous pores watertable. of greater diameter than normal soil matrix pore halophyte A terrestrial plant adapted morphologically spaces. Macropores can readily conduct water and/or physiologically to grow in saline conditions. when a soil is saturated. hydraulic conductivity The potential of a material to maximum field water content Maximum water content transmit fluids, expressed as a volume flow rate of of a soil two to three days after wetting, expressed water through a unit cross-sectional area of porous as weight/weight. medium under the influence of a hydraulic gradient montmorillonite See clay minerals. of unity, at a specified temperature. Hydraulic mottling In soils, spots, blotches or streaks of conductivity is measured in units of length/ subdominant colours that differ from the soil matrix time (commonly m/s or mm/d), and varies with colour. temperature. (Also called permeability.) necrotic / necrosis Death of circumscribed pieces hydraulic gradient Ratio of the change in hydraulic of tissue, such as patches on leaves. In plants, head between two points to the horizontal distance necrosis is an indicator of disease or plant stress between those two points. Maximum flow is usually that can be caused by salinity, wind, or high in the direction of the maximum fall in head per unit concentrations of specific ions in the soil solution. of horizontal distance, that is, in the direction of the maximum hydraulic gradient.
162 Glossary perched watertable Upper surface of a localised saline water A water containing sufficient unconfined aquifer separated from the underlying concentrations of soluble salts to limit plant groundwater by an unsaturated zone. productivity under certain environmental and piezometer A tube, open to water flow at a determined management conditions or to depth, sealed along the rest of its length, and otherwise limit the potential uses of the water. open to the atmosphere at the top, in which the salinisation The process of salts accumulating in soils hydraulic head or elevation of the watertable can be or waters. (Also called salting.) measured at a specified point in the groundwater. salinity The presence of soluble salts in or on soils or Technically, this measure of hydraulic head is only in waters. High levels of soluble salts may result accurate under no-flow conditions, but groundwater in reduced plant productivity or plant death and flow is usually slow enough for the measurement to may limit its suitability for various purposes. The be reasonably accurate. salinity of a water, soil water extract or suspension plant available water capacity Amount of soil water is usually described by one or more of four stored between the field measured upper wet expressions: profile (approximating ‘field capacity’) and the dry • Electrical Conductivity (EC) is a measurement of profile (approximating ‘wilting point’) of a soil to the quantity of electricity transferred across a the depth of the active root zone. Usually expressed unit area per unit potential gradient per unit time as an equivalent depth of rainfall (mm). at a specified temperature. It is the reciprocal plant salt tolerance Measure of the tolerance of of electrical resistance, and increases with salt a plant species to saline conditions, usually concentration. Units are Siemens per unit length expressed as yield relative to non-saline (standard unit is dS/m). For soils, the common conditions. measurements are on 1:5 soil water suspension pores Voids in soil surrounded by soil materials and and soil saturation extract. created by the packing of mineral and organic • Total Dissolved Ions (TDI) is the sum of the particles. Pores can be filled by any ratio of air and analysed cations plus anions expressed as mass water. per unit volume at a specified temperature. The pore space The total continuous and interconnecting ions in the summation must include at least 2+ 2+ + 2– – 2– – void space in a soil. Ca , Mg , Na , CO3 , HCO3 , SO4 and Cl . (This measure is equivalent to Total Soluble porosity Percentage of the total bulk volume of a Salts—TSS). material or soil that is occupied by void or pore space, measured either as total pore space • Total Dissolved Solids (calculated) (TDS calc) (absolute porosity) or as interconnected pore space is total silica plus the sum of the cations and – capable of conducting fluids (effective porosity). anions minus [HCO3 x 0.5083] expressed as mass per unit volume at a specified potentiometric surface Hypothetical surface, defined temperature.‑The ions in the summation must by hydraulic head in an aquifer and mapped include at least Ca2+, Mg2+, Na+, CO 2–, HCO –, from observations at piezometers or observation 3 3 SO 2– and Cl–. The bicarbonate correction boreholes, indicating directions of groundwater 4 allows for the conversion of HCO to CO on flow in the aquifer. The slope of the potentiometric 3 3 evaporation. (This measure approximates TDS by surface defines the hydraulic gradient and the evaporation.) horizontal direction of groundwater flow. This concept is strictly only applicable to systems where • Total Dissolved Solids (evaporation) (TDS horizontal flow is much greater than vertical flow. evap) is the weight of material remaining after evaporation of the sample filtrate and drying to recharge area Area in the landscape where the a constant weight at a specified temperature, net movement of water is downwards into and expressed as mass per unit volume. ‘recharging’ the groundwater. (Also sometimes referred to as an intake area.) The temperature of any measurement should be stated. The accepted standard temperature in root zone Depth of the upper soil in which the majority of Australia is 25°C. Conversion of EC measurements rooting activity occurs. Commonly down to 1200 mm. to standard or other temperatures (for soils and saline See salinity. waters generally) is described in Wells (1978). saline soil A soil containing sufficient concentrations salt flat Saline area associated with a shallow or of soluble salts within the soil profile to result in seasonally shallow saline watertable sufficiently reduced plant productivity or plant death. Climate, close to the soil surface to cause concentration of soil type, depth to salinity in the soil and plant salts in the root zone or on the soil surface. species influence the effect on plant productivity.
Glossary 163 salt marsh A coastal area periodically inundated with solonetz Dark coloured soil formed from a solonchak sea water, or area where a saline watertable occurs (light coloured soil with high concentrations of at or near ground level, supporting characteristic soluble salts such as sodium sulfate and sodium salt-adapted vegetation. chloride) by leaching of some of the sodium. salt pan Saline area associated with a permanent or Solonetz soils are highly alkaline and develops a seasonal seepage of saline water, or an area where columnar structure when dry. Occurring in semiarid, the watertable is seasonally or permanently at tropical environments, a solonetz soil profile will ground level. have a sandy, acid A horizon with a B horizon partially enriched with sodium clay. salt scald An area, bare of vegetation, where erosion of the surface soil has exposed a saline or sodic standing water level See watertable. subsoil. See also scald. subsurface outflow Groundwater exiting a catchment salting See salinisation. as subsurface flow. saturation extract An extract of the soil solution made Total Dissolved Ions See salinity. at soil saturation water content. Total Dissolved Solids See salinity. saturation water content Water content of a soil at Total Soluble Salts See salinity. which the soil contains the maximum amount of transmission area Area in a catchment where the net water it can hold when all pore spaces are filled movement of water in the groundwater is lateral with water. (approximately parallel to the soil surface) rather scald Area where erosion of surface soil has exposed than vertical. subsoils that remain bare of vegetation. Scalds can transmissivity Rate at which water can be conducted be saline or non-saline, sodic or non-sodic. through a unit width of aquifer under a unit seedbed Surface layer of soil which has been hydraulic gradient (units are m3/day/m). prepared to promote the germination of seeds and transpiration See evapotranspiration. the growth of seedlings. watertable Upper surface of a zone of saturation in an seepage salting A form of watertable salting occurring unconfined aquifer, which will be at atmospheric when water seeps, seasonally or permanently, at pressure. Below the watertable, the aquifer material the soil surface, causing salinity either directly or by is permanently saturated; above the watertable, evaporative concentration. (Non-saline seepages the rock or soil is unsaturated. The ‘depth’ of the without salting can also occur.) watertable is measured relative to the soil surface sodic soil Soil with a high percentage of sodium as standing water level (SWL). The watertable is ions (in soluble or exchangeable form), exhibiting also referred to as the phreatic surface, and below degraded soil behaviour such as dispersion when the watertable is the phreatic zone. wet and crusting when dry. watertable salting Salinity that occurs where a sodicity The presence of a high proportion of sodium shallow or seasonally shallow watertable is ions relative to other cations in a water or soil (in sufficiently close to the soil surface for groundwater exchangeable and/or soluble form). to move upwards to the soil surface by capillary Sodium Adsorption Ratio (SAR) Relative content action or seepage, resulting in the evaporative of sodium to calcium and magnesium in a soil accumulation of salts in the root zone or on the soil solution or water that approximates the ESP of surface. Watertable salting does not necessarily the soil. The relationship between SAR and ESP is involve saline groundwater. based on the Gapon ion exchange relationships. soil strength Measure of the capacity of a soil to withstand stresses without collapsing or becoming deformed. Consequence of lack of structure in dispersed (sodic) soils. Soil strength can prevent root penetration. solodic soil Leached, formerly saline soil, associated with semiarid tropical environments, in which the A horizon has become slightly acid and the B horizon is enriched with sodium-saturated clay.
164 Glossary Index
abbreviations ...... xv Callide area ...... 9, 41, 49, 149 absolute porosity ...... 163 capillary fringe ...... 161
Adaptive Environmental Assessment ...... 97 carbon dioxide ...... 74 and Management tool catchment groundwater ...... vi, 29, 69–73 aeolian deposits ...... 11 balance estimation aerial photography ...... 39, 45, 51, 88 catchments defined ...... 161 air pumps ...... 113–114 management software ...... 141 airborne geophysics ...... 45 restrictions ...... 40, 120–121 see also electromagnetic induction catena form ...... 39–40, 120 airborne multi-spectral scanner ...... 45 cation exchange capacity ...... 161 alluvial fans ...... 40, 120 CCR ...... 161 alluvial valleys ...... 40, 121 CEC ...... 161 aquifers ...... 10, 28, 161 CEC to clay content ratio ...... 161 see also transmission areas central Queensland area ...... 39, 40, 41, 42 area units ...... xvi see also specific areas AUSTRALIAN RAINMAN (software) ...... 141 ceramic salinity ...... 61 average annual rainfall ...... 12, 29, 55–56 chemical concentrations average root zone salinity ...... 34 converting measures ...... 158–160 salt in rainfall ...... 10 Ayr area ...... 12 units defined ...... xvi basalt form ...... 39, 120 chloride ...... 54, 76 base flow ...... 161 see also EC1:5/ECCl; ECCl benefit–cost analyses ...... 96 Clare area ...... 57
Biloela area ...... 149 class A pan evaporation ...... 161
Boonah area ...... 40, 41 clay minerals defined ...... 161 boron ...... 54, 81 measures ...... 161 Bowen area ...... 150 relevance to salinity investigations ...... 59 sodicity effects ...... 23–26 bulk density ...... 160 clearing, Bundaberg area ...... 8, 13, 148 see vegetation
Burdekin area Clermont area ...... 49 groundwater flow ...... 40, 41 indicator species for salinity risk ...... 49 climate irrigation water salting ...... 9 affecting plant salt tolerance ...... 53 rainfall effect on salting ...... 57 contributions to salinity risk ...... 11–12 salinity investigations ...... 150–151 salinity investigations ...... 28–29, 55–56 watertable salting ...... 8, 11 software ...... 141 see also rainfall calcium ...... 75, 80 see also gypsum Collinsville area ...... 151
Index 165 common ion effect ...... 74–75 drinking water ...... xii, 29, 79 concretions ...... 59 dryland farming ...... 161 see also crops and cropping; pastures Condamine catchment area ...... 147 dykes ...... 41, 122 confined aquifers ...... 161 EC (electrical conductivity) costs ...... xii, 96 of 1:5 soil:water suspension, cover ...... 101 see EC1:5 see also mulching conversions to other measures . . 30–33, 158–160 defined ...... 30, 161 crops and cropping due to chlorides, contributions to salting ...... 88 see ECCl plant salt tolerance . . . . . 103, 117, 124–128 as a measure of salinity ...... 30–33 as revegetation option ...... 101, 103–104 meters ...... 65 selecting with software ...... 142 of soil saturation extract, water balance software ...... 141 see ECse yields ...... xi, 51–53 units ...... xvi dams ...... 42, 123 at water content approximating to field capacity,
see ECs Darling Downs
groundwater flow ...... 39, 40 EC1:5 salinity investigations ...... 146–147 conversion to ECCl ...... 158 salinity outbreaks noted after rainfall . . . . . 12 defined ...... 30 measuring salinity ...... 30–33, 60–61 decision-making processes ...... 92–97
EC1:5/ECCl ...... 31–32 Dee River area ...... 8, 9, 41, 149
ECCl ...... 41, 195 deep drainage rate ...... 72
see also catchment groundwater balance ECs 3 9 ...... 30 estimation ECse ...... 30–32 deltaH, educational material ...... 142 see hydraulic gradient effective porosity ...... 163 depth to watertable measurement ...... 65–70 effluent ...... xiii, 110 diesel pumps ...... 113 electric pumps ...... 113 Dimbulah area ...... 8 electrical conductivity, discharge areas see EC defined ...... 161, 162 locating by investigation ...... 28, 29 electromagnetic induction ...... 45, 46–48, 61 processes ...... 16–18, 62 Elliott River area ...... 49 springs ...... 15 vegetation management . .99–100, 106, 137–140 Emerald area water use as a management option . . . .95–96 removal of salts from profile ...... 23 see also seepages; waterlogging root zone salinity ...... 35–37 salinity investigations ...... 150 dispersion ...... 23–26, 161 watertable salting ...... 8 domestic use of water ...... xii, 29, 79 engineering management of salinity . . . . 110–114 Don River area ...... 149 environmental features ...... 11–13 drainable porosity ...... 161 see also climate; human activities; landscape . . features drainage ...... 89, 71–73, 110–111 see also effluent; pumps and pumping erosion ...... 9 see also aeolian deposits drilling methods ...... 68
166 Index ESP, Grafton area ...... 10 see exchangeable sodium percentage grain crops, evaporation rate ...... 11–12, 14, 72 see crops and cropping see also class A pan evaporation grasses, evapotranspiration ...... 14, 72, 162 see pastures see also water consumption grazing control ...... 101, 103, 107 exchangeable sodium percentage Great Artesian Basin ...... 4, 15 conversion from SAR ...... 158 defined ...... 37–38, 162 groundwater, determining ...... 37–38 balance ...... 22, 70–72 measure of soil cations . . . . . 63–64, 84–85 defined ...... 162 field test of quality ...... 67 farm records ...... 29, 88 landform influencing flow ...... 39–42 see also crops and cropping; pastures mapping with piezometers ...... 29 faulting ...... 41–42, 123 modelling ...... 15–17, 70–73, 141 removal ...... 110–114, 141–142 fertilising ...... 103, 107 salt sources ...... 10, 28–29, 73–78 fertility, soil ...... 53 using for irrigation ...... xiii–xiv see also aquifers; discharge areas; recharge and field capacity ...... 162 recharge areas; watertables see also ECs; plant available water capacity growth stages of plants ...... 53, 103 fire breaks ...... 107 gypsum ...... 118, 160 flats ...... 163 halophytes ...... 52, 162 flocculation ...... 23–26, 162 historic land use ...... 29, 88–89 flood irrigation ...... 116 see also information sources fluoride ions ...... 81 historic salt loads ...... 13, 28 forage ...... 137–140 historical societies ...... 88 see also pastures honey production ...... 137–140 frost resistance ...... 105, 137–140 human activities ...... 13, 29 frost tolerance ...... 100, 105, 137–140 human use of water ...... xii, 29, 79 fruit, see crops and cropping hydraulic conductivity ...... 19, 72, 162 furrow irrigation ...... 116, 118 hydraulic gradient ...... 20, 72, 162 see also transmissivity geological faulting ...... 41–42, 123 hydraulic head ...... 162 geology see also piezometers maps and surveys ...... 39, 42–43 salinity investigations ...... 28 hydrology ...... 14–21, 141, 162 alinity risk investigations ...... 42–44 illites ...... 23–26, 161 geomorphic features, indicator species ...... xii, 28, 49–51 see geology; landform features information sources geophysics ...... 45–48, 61 advice ...... xiv germination ...... 53, 103 catchment groundwater balance estimation 71–72 geology ...... 42 Gladstone area ...... 10, 148 historic land use ...... 88–89 gleyed soils ...... 162 landform features ...... 39 plant indicators of salinity ...... 49 glycophytes ...... 52
Index 167 plant responses to salinity ...... 51 LANDSAT imagery ...... 43, 88 rainfall data ...... 55–57 landscape features remote sensing images of vegetation . . . . . 51 identification ...... 39–42, 120–123 soil salt profiles ...... 61–63 salinity investigations ...... 28, 39–48 soils ...... 58 leaching ...... 116, 162 Ingham area ...... 151 see also leaching fraction Inglewood area ...... 145 leaching fraction ...... 22–23, 32–34, 36–37 insect attack ...... 107 leaky aquifers ...... 161 intake areas, length units ...... xvi see recharge and recharge areas Lockyer Valley interception trenches ...... 111 catchment groundwater balance estimation 70–73 ions delayed salting caused by clearing ...... 13 presence in water ...... 73–78 determining probable source of groundwater 77–78 sources ...... 10, 28, 29, 73–78 groundwater flow ...... 40, 41 toxicity of irrigation water ...... 86 irrigation water salting ...... 8, 9, 82–84 predicting LF ...... 34 Ipswich area ...... 146 rainfall effect on salting ...... 57 irrigation relationship between land use and salting . . 89 equipment ...... 86 removal of salts from profile ...... 24 influencing plant salt tolerance ...... 53 salinity investigations ...... 146 LF estimations ...... 32–34 Mackay area ...... 150 management of salinity . . 29, 115–118, 142–144 see also irrigation water macropores ...... 162 irrigation water magnesium ions ...... 75, 81, 82 effects on soil salinity ...... 23–24 magnetics ...... 45, 47 excessive nutrients ...... 86 publications on issues ...... 145 maps and mapping, salting ...... 9–10, 34, 82–84, 162 see groundwater; information sources; salinity suitability investigations . . . . xiv, 37, 102–106 see also leaching fraction; water salinity; water Mareeba area ...... 8, 40, 41 sodicity marshes ...... 162 kaolinites ...... 23–26, 162 Maryborough area ...... 8, 148
Kingaroy area ...... 39, 147 mass units ...... xvi laboratory analyses of waters ...... 73 maximum field water content ...... xv, 162
Lake Buchanan area ...... 42 Miles area ...... 147
Lake Eyre ...... 14, 42 Model for Effluent Disposal using Land Irrigation lakes ...... 42, 123 (MEDLI) (software) ...... 142 land survey reports, models ...... 14–17, 96–97, 141–144 see information sources MODFLOW (software) ...... 97, 141 land use, montmorillonite ...... 23–26, 85, 162 see crops and cropping; farm records; historic land use; mottling ...... 162 pastures; residential subdivision see also gleyed soils landform features mounding ...... 101 contribution to salinity risk ...... 13 Moura area ...... 149 defined ...... 162 factor in salinity investigations ...... 28 moving average rainfall pattern . . . . . 29, 56–57 identification ...... 39–42, 120–123
168 Index MSS imagery ...... 45 pores ...... 163 mulching ...... 103, 104, 107, 118 porosity ...... 163 multi-spectral scanner imagery ...... 45 potable water ...... xii, 29, 79 necrosis ...... 162 pressure units ...... xvi nitrate ions ...... 80, 81 primary salinity ...... 2
Normanton area ...... 4 Productivity, Erosion, Run-off Functions to Evaluate Conservation Techniques (PERFECT) (software) . . 141 Northern Tablelands area ...... 151 profiles, salt ...... 29, 61–63 nutrients in irrigation water ...... 86 Prosperpine area ...... 150 oil production ...... 137–140 Pumicestone Passage area ...... 147 ornamental species ...... 126, 129–132 Pump It (software) ...... 142 osmotic potential ...... 159 pumps and pumping ...... 112–114, 142 pans ...... 164 see also groundwater pastures Queensland Spatial Information revegetation ...... 101, 102–103 Directory (QSID) ...... 42, 88 salt tolerance 49–50, 102–103, 117, 126–128, 129, ...... 132, 133–136 radiometrics ...... 45, 47 salting process ...... 88 rainfall species indicative of salinity ...... 49–50 contributions to salinity risk ...... 10, 11–12 suitable for waterlogged areas . . . . . 133–136 factor in salinity investigations . . .28–29, 55–57 see also grazing control publications ...... 145 perched aquifers ...... 161 software ...... 141 tree requirements ...... 137–140 perched watertables ...... 17, 161, 163 RAINMAN (software) ...... 141 permeability, see hydraulic conductivity recharge and recharge areas defined ...... 15–16, 163 pH, soil ...... 58–59 distribution ...... 15 phreatic zone ...... 164 information derived from geology ...... 28 processes ...... 15–16, 62 piezometers ...... 29, 66–70, 163 soil salt profile investigations ...... 29 see also hydraulic head vegetation management ...... 98, 106 Planning, Research, Implementation, Monitoring and volume reduction ...... 94, 95 Evaluation (PRIME) decision support tool . . . . 97 reflectometry ...... 61 plant-available water capacity ...... 163 reforestation, see also field capacity see revegetation plant communities ...... xi, xi, 28, 49–51 remote sensing images ...... 28, 45, 50–51, 88 planting methods . . . . 102–103, 104–105, 106–107 See also aerial photography plants residential subdivision ...... 89 responses to salinity 28, 51–54, 84–85 residual alkali ...... 83 yields xi, xii, 51–52 see also crops and cropping; indicator species; restrictions to water flow ...... 29, 40, 121 pastures; plant communities; revegetation; trees revegetation ...... xiii, 99–100, 137–140 and shrubs see also plants ploppers ...... 65 risk, pore space ...... 163 see salting potential
Index 169 rock weathering ...... 10 ornamental species ...... 126, 129–132 pasture species Rockhampton area ...... 30, 40, 149–150 . . . 49–51, 104, 117, 126–128, 129–132, 133–136 root zone processes ...... 51–53 defined ...... 163 publications ...... 145 salinity ...... 34–37, 52 terminology ...... 52, 161 trees ...... 49, 126, 129–132, 137–140 Runoff, Storage and Irrigation Calculator (RUSTIC) (software) ...... 142 saltbush, see pastures runoff control ...... 101 salting SALF-SALFCALC (software) . . . . 30–32, 73, 141, 144 defined ...... 3, 164 SALF-SALFPREDICT (software) investigations ...... xi–xii, 28–89 ...... 32, 34, 61, 103, 115, 141, 144 processes in discharge areas ...... 16–18 see also irrigation water; salinity; salting potential saline soils, see soil salinity salting potential classification scheme ...... 48 saline water, contributions of environmental features . . 10–13 see water salinity distribution ...... 10–13 salinisation, predicting ...... xi–xii, 55 see salting related to salt loads ...... 13, 28 see also salt loads salinity, defined ...... 2, 162 SAR, investigations . . . . .28–29, 108–109, 145–151 see sodium adsorption ratio management ...... xii–xix, 22–23, 92–118 Sarina area ...... 40 mapping ...... 29, 43–48 overview ...... 2–13 saturation extracts ...... 61, 164
plant indicators ...... xii, 28, 49–51 see also ECse root zone ...... 34–38 saturation water content ...... 164 survey publications ...... 145 see also EC (electrical conductivity); salting; scalds ...... 164 salting potential; soil salinity; water salinity scientific units ...... xvi Salt, Water and Groundwater secondary salinity ...... 2 Management (software) ...... 142 seedbed ...... 164 salt flats ...... 163 seepages ...... 3, 6, 72, 164 salt loads ...... 13, 28 see also discharge areas salt marshes ...... 164 seismic refraction ...... 47 salt mass balance ...... 17–19 semi-unconfined aquifers ...... 161 salt pans ...... 164 semiconfined aquifers ...... 161 salt profiles ...... 29, 61–63 shade and shelter from trees ...... 137–140 salt-resistant plants ...... 52 shire handbooks ...... 88 salt scalds ...... 164 SIRAG (software) ...... 142 salt sources ...... 10–11, 28, 29, 73–78 site planning ...... 106–107 salt tolerance site preparation for revegetation . . . . . 100, 106 crop species ...... 104, 117, 124–132 see also planting methods defined ...... 164 factor in choosing revegetation species . . . 100 smectite group, native species ...... 49–50, 105 see montmorillonites
170 Index sodic soils, solodic soil ...... 164 see soil sodicity solonetz ...... 164 sodic water, solubility of salts ...... 74–75 see water sodicity South Burnett area ...... 147 sodicity see also chemical concentrations defined ...... 2, 164 SPOT imagery ...... 45 overview ...... 2–13 survey publications ...... 145 spray irrigation ...... 116–117, 118 sodicity tolerance ...... 100 springs ...... 15
SODICS (software) ...... 33, 142 sprinkle irrigation ...... 116–117, 118 sodium adsorption ratio standing water level ...... 164 conversion to ESP ...... 158 see also depth to watertable measurement; defined ...... 38, 164 watertables as a measure ...... 38, 63–64 predicting irrigation water effect ...... 85 stock control ...... 101, 103, 107 sodium ions stock water ...... xii, 29, 79–81 sources ...... 75 stratigraphic form ...... 41, 122 toxicity to plants ...... 53–54 see exchangeable sodium percentage; salting; stream confluences ...... 41, 122 sodicity subsurface water ...... 110–11, 164 software packages ...... 141–144 suction units ...... xvi soil salinity sulfur ions and compounds classified according to plant salt tolerance . . 62 harmful to stock ...... 81 controlled by managing LF ...... 22–24 reducing sodicity of irrigation waters . . .117–118 factor in salinity investigations ...... 29 sources ...... 75 measurement ...... 60–62 software ...... 141 sun-powered pumps ...... 113 soil salt profiles surface waters ...... 67, 110 factor in salinity investigations ...... 29 see also runoff control relevance to salinity investigations . . . . 61–63 survey reports, soil sodicity see information sources defined ...... 164 SWAGMAN OPTIONS (software) ...... 142 distribution ...... 3–5 effect on soil stability ...... 23–26 SWAGMAN WHATIF (software) ...... 142 measurement ...... 37–38 SWAGSIM (software) ...... 141 plant indicators ...... 49 publications ...... 145 tannin production ...... 137–170 response to irrigation ...... 84–85, 118 TDI ...... 159, 164 salinity investigations ...... 29, 63–64 suitable tree species ...... 137–140 TDS ...... 159, 164 soil solution displacement ...... 61 temperature ...... xvi, 163 soil solution extraction ...... 61 tensiometers ...... 29, 66–70, 162 soils Thematic Mapper imagery ...... 45 chemical properties ...... 53, 58–60 conversion of volume and density measures . 160 timber products ...... 137–140 physical properties . . . . . 23–26, 29, 160, 164 time domain reflectometry ...... 61 publications ...... 39, 62, 63, 145 response to irrigation ...... 29 time units ...... xvi salinity investigations ...... 29, 58–64 TM imagery ...... 45 salt profiles ...... 29, 61–63
Index 171 tolerance, water level contours ...... 29 see frost tolerance; salt tolerance; sodicity water management, tolerance see engineering management of salinity; irrigation TOPOG-IRM (software) ...... 141 water quality total dissolved ions ...... 159, 164 field measurement ...... 65 publications ...... 145 total dissolved solids ...... 159, 164 salinity investigations ...... 29 total soluble salts, suitability for different uses ...... xii, 79–87 see total dissolved ions see also water salinity transmission areas water salinity defined ...... 164 defined ...... 163 intercepting water in ...... 95, 96 field measurement ...... 65 processes ...... 16 irrigation issues ...... 81–85 vegetation management ...... 99, 106 stock issues ...... 79–81 transmissivity ...... 164 water sampling ...... 67 see also hydraulic gradient water sodicity transpiration effects on soil salinity ...... 23–24 see evapotranspiration irrigation issues ...... 81–85, 116–118 measurement ...... 37–38 trees and shrubs see also exchangeable sodium percentage revegetation ...... 102, 104–107 salinity management ...... 137–140 waterlogging salt tolerance . . .49–50, 126, 129–132, 137–140 factor in choosing revegetation species . . . 100 vegetation management . . .xiii, 88–89, 98–109 history revealed in soil properties ...... 29 suitable plants ...... 105, 134–136 trickle irrigation ...... 117 see also discharge areas trilinear diagrams ...... 76–78 waters ...... 29, 65–78 TSS, see also groundwater; irrigation water; water see total dissolved ions quality unconfined aquifers ...... 161 WATERSCHED (software) ...... 142 units, scientific ...... xvi watertables critical depth to prevent salting ...... 22 vegetables, depth to ...... 65–70 see crops and cropping rise limited ...... 115–116 vegetation salting ...... 6–7, 16–18, 29, 164 influence on hydrology ...... 14 see also perched watertables; waterlogging management ...... xiii, 88–89, 98–109 weathering ...... 10 patterns ...... 50–51 see also leaching salinity investigations ...... 28–29, 49–54 see also plants weed control ...... 107 vegetative cover ...... 101 wind erosion, see also mulching see aeolian deposits vermiculites ...... 23–26 wind-powered pumps ...... 113 void ratio (soils) ...... 160 windbreaks ...... 137–140 volume units ...... xvi Wmax ...... xv water consumption ...... 101, 143–144 yields ...... xi, xii, 51–53
172 Index