The a Horizons Can Be Broken Down Into Three Distinct Layers
Total Page：16
File Type：pdf, Size：1020Kb
Soil Glossary
A HORIZONS: The surface mineral horizons where some have organic matter accumulation. They are usually darker in colour than the lower horizons. If they are lighter in colour, then the horizons have lower silicate clay and/or sesquioxide content (McDonald et al., 1990).
The A Horizons can be broken down into three distinct layers: A1 Horizon - Soil surface (if no O Horizon present) with some organic matter content. Usually darker in colour than horizons below with biological activity. Can be subdivided into A11, A12, A13 etc. subhorizons. A2 Horizon - It is usually paler in colour from the A1 horizon. It can have less organic matter, sesquioxides, silicate clay. A3 Horizon - Transitional horizon between the A and B horizons but has predominantly A Horizon properties. ACIDIC: Soils with a pH less than 7.0 in water. While some plants thrive in acid soils, others don't and require lime to make the soil more alkaline. This term is also used as a Subgroup distinction for a number of Soil Orders in the Australian Soil Classification (Isbell, 1996). It refers to soils with a B2 horizon that on the whole is strongly acid.
ACIDIFICATION: The process whereby soils become acidic over time as a result of: the parent material; the addition of nitrogen to the soil by either fertiliser or legumes (where nitrogen is converted to nitrate); and/or the leaching of the soil by rainfall. AEOLIAN: A geomorphic process whereby soil forming material is transported and deposited by wind.
AERIC: This term refers to soils that are rapidly drained throughout the whole profile. The B horizons are weakly coherent and porous and are often brightly coloured. This term is used as a suborder to describe Podosols in the Australian Soil Classification (Isbell 1996).
AEROBIC: Soils in which free oxygen is abundant and chemically oxidising processes prevail. This usually occurs in well drained soils with good structure.
ALLUVIAL: Alluvial refers to sediment deposition in riverine landscapes.
ALLUVIUM: Alluvium is the sediment deposited from transportation by channelled stream flow or over-bank stream flow.
ANAEROBIC: These are soils that are deficient in free oxygen and where reducing processes predominate. This condition generally occurs in poorly drained or waterlogged soils. Water has replaced the air, resulting in a bluey-grey coloured soil.
ANGULAR BLOCKY STRUCTURE: A cube-shaped ped where soil particles are arranged around a point, bounded by six relatively flat, roughly equal faces. See also sub-angular blocky.
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 1 of 27 ANTHROPOSOLS: These soils result from human activity e.g. mine spoil where origin soils may be buried and new parent material introduced. A Soil Order of the Australian Soil Classification (Isbell, 1996).
Ap HORIZON: The A horizon is the surface of the soil. The 'p' denotes disturbance by man e.g. ploughing, deep ripping. Mc Donald et al. (1990).
APEDAL: These soils are either single grained (incoherent) or massive (coherent). Peds are not apparent when the soil is moderately moist.
AQUIC: These soils have stagnant water on the soil surface and/or can be saturated in some part of the upper 0.5 m of the profile, more or less continuously for 2 to 3 months. In this condition, the soil is free of dissolved oxygen. Gley (bluey-grey) colours are often an indication of prolonged saturation. The definition is used as a Suborder distinction for Podosols and Vertosols in the Australian Soil Classification (Isbell, 1996).
ARENIC: Soils in which at least the upper 0.5 m of the profile is non-gravelly and of sandy texture throughout. It is also loosely or weakly coherent (see consistence) and may have aeolian (wind- blown) cross-bedding. This term is used in the Australian Soil Classification (Isbell, 1996) to describe Rudosols and Tenosols.
ARGIC HORIZON: A subsoil horizon consisting of distinct lamellae that are sharply defined, horizontal to sub-horizontal layers that have a higher clay content than adjacent sandy or sandy loam material, usually 5 to 10 mm thick. Consistence is stronger and the colour usually darker and more reddish or brownish than the surrounding soil. This term is used as a definition for Calcarosols, Kandosols and Tenosols in the Australian Soil Classification (Isbell, 1996).
Argic horizons in a sandy Tenosol in the Wimmera region.
AUSTRALIAN SOIL AND LAND SURVEY - FIELD HANDBOOK (The Yellow Book) : Mc Donald et al. (1990). This handbook specifies methods, standards and terminology used for the description of soil sites. It provides a national reference set of definitions and has been designed for field use.
AUSTRALIAN SOIL CLASSIFICATION: (Isbell, 1996) The Australian Soil Classification was developed by Ray Isbell (CSIRO Land and Water) in collaboration with land resource assessment staff throughout Australia. It serves as a framework for organising knowledge about Australian soils and provides a means of communication amongst scientists and those who use the land. It is useful for those involved in environmental studies and for teachers of soil science. The Australian Soil Conservation Council formally endorsed the new classification in 1992 and recommended its adoption by all States and Territories and its use in all future Federally funded land resource inventory and research programs.
The classification scheme operates using a hierarchical system and is based on Australian soils data that is significant with regard to land management. The general form of the nomenclature is: Subgroup, Great Group, Suborder, Order; family (e.g. Bleached, Eutrophic, Red CHROMOSOL; thick, sandy)
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 2 of 27 The Australian Soil Classification was published in May 1996 and is available from CSIRO Publishing, PO Box 1139, Collingwood, Victoria, Australia 3066, for around $30 including postage.
An Australian Soil Classification Online (external link) version exists on the Australian Collaborative Land Evaluation (ACLEP) website under ACLEP activities.
B HORIZON: Subsoil horizons consisting of one or more mineral layers differing to the A Horizon by: clay, iron, aluminium or organic matter concentrations; structure and/or consistence; colour. The B Horizons can have one or more of the following layers: B1 Horizon - Transitional layer between the A and B horizons but dominated by B Horizon properties. B2 Horizon - Has the dominant feature of greater clay, iron, aluminium, humus and/or maximum development of pedological organisation. May be divided into subhorizons B21, B22, B23 etc. B3 Horizon - Transitional layer between the B and C horizons, dominated by B Horizon properties but integrating into the C material below (McDonald et al., 1990). BASE STATUS: Is a ratio relating the major nutrient cations (Ca, Mg, K and Na) to the clay percentage in the soil. It is used as an indicator of soil fertility and is expressed in cmol (+) kg-1 clay. It is calculated by multiplying the sum of the reported basic cations by 100 and dividing by the clay percentage of the sample.
Three classes are defined: dystrophic - if the sum is less than 5 (indicating low inherent fertility and/or strongly weathered profile); mesotrophic - if the sum is between 5 and 15 inclusive (indicating moderate inherent fertility and/or moderately weathered profile); and eutrophic if it is greater than 15 (indicating relatively high inherent fertility and/or low degree of profile weathering). It is used for some Great Group distinctions within the Australian Soil Classification (Isbell, 1996).
BASIC: This term is used to describe Tenosols, Organosols and Rudosols in the Australian Soil Classification (Isbell, 1996). It refers to soils that are not strongly acid or calcareous.
Bh HORIZON: A subsoil horizon notation whereby the 'B' refers to the B Horizon and the 'h' to the humic horizon. Organic matter and aluminium compounds are strongly dominant (with very little or no trace of iron compounds). This term is used as a definition for the Podosol Order in the Australian Soil Classification (Isbell, 1996). Bh horizon at 30-40 cm depth in a West Gippsland Podosol.
Bhs HORIZON: A subsoil horizon notation whereby the 'B' refers to the B Horizon and the 'hs' to the humosesquic horizon. Iron and organic compounds (often referred to as 'coffee rock') are prominent within the horizon and the organic compounds are distributed as streaks, patches or
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 3 of 27 lumps. Humosesquic is used as a (Bhs horizon) definition for the Podosol Order in the Australian Soil Classification (Isbell, 1996).
Bk HORIZON: A subsoil horizon notation whereby the 'B' refers to the B Horizon and 'k' to an accumulation of carbonates (usually calcium carbonate) within the associated horizon.
BLEACHED HORIZON: Horizons that are paler than adjacent horizons. They are best viewed when the soil is dry. A bleach is generally associated with the A2 horizon although it is not restricted to this layer. It generally occurs on top of a much less permeable subsoil, pan or hard rock. A conspicuously bleached horizon is one in which 80% or more of the horizon is bleached. A sporadic bleach occurs irregularly throughout the horizon or as blotches at the interface of the A and B horizons (Northcote, 1979). This horizon is the most leached part of a soil. Organic matter, clay, iron, aluminium and nutrient elements have all been removed, leaving an accumulation of silica giving the horizon its whitish colour. Field observations have established that bleached horizons are often saturated with water and their occurrence is usually an indication of periodic waterlogging. This can indicate sodic subsoils where there is a strong texture contrast between A and B horizons.
BLOCKY STRUCTURE: A cube shaped ped. See also sub-angular blocky and angular blocky.
Bs HORIZON: A subsoil horizon notation whereby the 'B' refers to the B horizon and the 's' to the sesquic horizon. Iron compounds are strongly dominant or codominant (with aluminium) and there is little evidence of organic matter. Sesquic is used as a Great Group definition for the Podosol Order in the Australian Soil Classification (Isbell, 1996).
BUCKSHOT: Describes generally rounded, hard (small to medium sixed) ferruginous concretions.
BUFFERING CAPACITY: The soils ability to resist change in pH. Soils with a high clay and organic matter content have a higher buffering capacity and can tolerate the addition of acidifying fertilisers over an extended period, or at a higher rate of addition without becoming too acid. But once it is acid, the soil will require a large amount of lime or dolomite to reverse the effect. The amount of lime or dolomite required varies from soil to soil depending on the pH (Baker and Eldershaw, 1993).
CALCAREOUS: It describes a soil that has sufficient calcium carbonate to cause effervescence after the application of a few drops of hydrochloric acid. The calcium carbonate can either be in the form of carbonate segregations or fine earth. Calcareous is used as a descriptive term for Ferrosols, Hydrosols, Organosols, Rudosols and Tenosols in the Australian Soil Classification (Isbell, 1996).
CALCAROSOL: A Soil Order of the Australian Soil Classification (Isbell 1996). These soils are either calcareous throughout the solum (or at least directly below the A1 horizon or at a depth of 0.2 m, which ever is shallower) and do not have clear or abrupt textural B horizons. The carbonate must have resulted from soil forming processes.
CALCRETE: A layer where cemented carbonate accumulation has occurred. The material must be hard in a pan or in the substrate. This definition does not describe the common soft carbonate nor the carbonate accumulated in nodules or concretions. This term is used to describe a number of soils in the Australian Soil Classification (Isbell, 1996). Calcrete layer at 20 cm depth in a Calcarosol near Walpeup.
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 4 of 27 CALCIC: These soils have a Bk horizon or a subsurface layer containing 2 - 20% soft carbonate and 0-20% hard calcrete fragments and/or carbonate nodules. This term is used to describe a number of Soil Orders in the Australian Soil Classification (Isbell, 1996).
CEC (CATION EXCHANGE CAPACITY): Is the measure of the capacity of a soil to hold the major cations: calcium, magnesium, sodium and potassium (including hydrogen, aluminium and manganese in acid soils). It is a measure of the potential nutrient reserve in the soil and is therefore an indicator of inherent soil fertility. An imbalance in the ratio of cations can result in soil structural problems. High levels of individual cations (e.g. aluminium and manganese) can also be toxic to plants.
CEMENTED: Indurated substances such as humus, calcium carbonate and the oxides of silicon, iron and aluminium can bind soil particles together in a hard brittle mass. This hardened state persists even when wet.
C HORIZON: Layers below the solum (AB profile) lacking pedological development. Includes consolidated rock and sediments that are generally weak in strength.
CHROMOSOL: Soil Order of the Australian Soil Classification (Isbell, 1996). Soils with a clear or abrupt textural change at the B2 horizon where the pH is 5.5 (water) or greater in the upper B2 horizon. The B2 horizon is often brightly coloured.
COFFEE ROCK: A compacted, cemented or indurated layer within the profile that is comprised of humus and iron oxides.
Thick coffee rock layer (Bhs horizon) from 80 cm depth in a Cranbourne Podosol. Thinner irregular coffee rock layer (Bhs horizon) at 80 cm depth in a Cranbourne Podosol.
COLLOIDS: Fine clay and organic matter material with a particle size of less than 0.002 mm in diameter. These particles tend to remain permanently in suspension unless flocculation (aggregation of particles that settle out) occurs.
COLOUR: Soil colour is assessed in a moist condition using a Munsell Colour Chart (Munsell Colour Company, 1975) to assess the dominant colour. Secondary colours, bleaches and mottles are also recorded. Colour provides a useful indication of a number of profile attributes. Dark surface soils, for instance, indicate a high level of organic matter. In a subsurface A2 horizon, bleached colours indicate low levels of plant nutrients and that seasonal or periodic waterlogging occurs. In subsoils, the colour sequence from red to brown or yellow to grey colours, indicate a sequence from well aerated and well drained soils to poorly aerated and poorly drained soils.
The tables below are used to obtain colour classes in the Australian Soil Classification (Isbell, 1996).
COLUMNAR STRUCTURE: Soil particles are arranged around a vertical axis with flat faced peds. The tops of the columns have clearly defined domes. Columnar structure is often associated with subsoil sodicity.
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 5 of 27
Columnar structure in the subsoil of a Corangamite Sodosol.
COMPACTION: The process whereby soil density is increased as a result of tillage, stock trampling and/or vehicular trafficking. Compaction can lead to lower soil permeability and poorer soil aeration resulting in increased erosion hazard and poorer plant productivity. Deep ripping and conservation tillage can alleviate the condition.
CONCHOIDAL FRACTURING: A mass of soil which has obvious concave fracturing (ball and socket appearance). This is associated with severe compaction and remoulding (disturbed in a moist to wet conditon.). It is best seen in a soil pit exposure when material is removed with a mattock or pick and has the appearance of fractured bluestone.
Conchoidal fracturing is most likely to occur just beneath the surface of clay soils (Vertosols) and if the soil has been compacted (e.g. vehicular traffic) whilst in a moist to wet condition (i.e. wetter than the plastic limit) for prolonged periods. Conchoidal fracturing is evident in the 10 - 30 cm zone of this Grey Vertosol.
CONSISTENCE: Consistence indicates a soils resistance to deformation and is a measure of the degree of cohesion. It is measured by the resistance of a ped to deformation between the thumb and forefinger. According to Australian Soil and Land Survey Field Handbook (Mc Donald et al. (1990) consistence can be measured on a scale of 1 (small force required) to 7 (rigid force required). This varies depending on the soil water content. Consistence relates to the texture and structure of a soil and is a measure of its workability and stability, or behaviour when manipulated e.g. friable soils are easier to work than hard soils.
0 Loose No force required, separate particles such as loose sand. 1 Very weak Very small force. 2 Weak Small but significant force. 3 Firm Moderate or firm force. 4 Very firm Strong force but within the power of the thumb and forefinger. 5 Strong Beyond power of thumb and forefinger but crushes underfoot on hard flat surface with small force e.g. a shovel. 6 Very strong Crushes underfoot on hard flat surface with full body weight applied slowly. 7 Rigid Cannot be crushed underfoot by full body weight applied slowly.
CRUMB STRUCTURE: Rounded peds less than 12 mm in diameter which are unstable and tend to crumble into smaller units. This type of structure is associated with surface horizons.
CRUSTY: Soils with a massive or weakly structured surface crusty horizon (3 cm or less thick). It is often lower in clay content than the underlying non-self mulching structured clay. This term is used as a Great Group definition for Vertosols in the Australian Soil Classification (Isbell 1996).
Crusty surface soil in northern Victoria.
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 6 of 27 Soil Glossary D-G A-C | D-G | H-R | S-Z | References | Soil Homepage
D | E | F | G
DERMOSOLIC: This is a term used as a Great Group distinction to describe Hydrosols in the Australian Soil Classification (Isbell, 1996) indicating that they have a structured B2 horizon. Apart from saturation of the greater part of the profile for prolonged periods (2-3 months) in most years, these soils would otherwise have been classified as Dermosols.
DERMOSOLS: Soil Order of the Australian Soil Classification (Isbell, 1996). Soils that have structured B2 Horizons more developed than weak throughout the major part of the horizon. They also lack strong texture contrast between the A and B horizons.
D HORIZON: Any soil material below the solum that is unlike the solum and C Horizon and is not a buried soil (McDonald et al, 1990).
DISPERSIBLE SOILS: Soils that are structurally unstable and disperse in water into basic particles i.e. sand, silt and clay. Dispersible soils tend to be highly erodible and present problems for successfully managing earth works (See Dispersion).
DISPERSION: Dispersion is an indicator of sodic soils as it occurs when excessive sodium is present. When water is added, the sodium attaches to the clay and forces the clay particles apart. This results in a cloud of clay forming around the aggregate. The fine clay particles that have dispersed, clog up the small pores in the soil and degrade soil structure as well as restricting root growth and water movement. Dispersive soils usually have a high Exchangeable Sodium Percentage (ESP). See Aggregate Slaking and Clay Dispersion and Dispersion in the Soil Health section of this website..
Gypsum (calcium sulphate) can be used as an ameliorant for dispersive soils. Gypsum initially provides an electrolyte effect to the soil, increasing its salt concentration. This prevents clay particles from swelling and therefore reduces dispersion. A longer term effect of gypsum is to replace exchangeable sodium attached to clay particles with exchangeable calcium which makes the soil less sodic and reduces dispersion.
The petri dish on the left has three surface soil aggregates from the one soil at the top and three subsoil aggregates at the bottom. Note that no dispersion has occurred for the surface soil but that strong dispersion has occurred with the subsoil aggregates. The petri dish on the right has the same surface and subsoil aggregates placed in a gypsum solution. Note that no dispersion has taken place. This illustrates the immediate electrolyte effect of gypsum.
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 7 of 27 The same soil type (as above) has been wet up and remoulded (rolled into a ball) for the surface and subsoil and then placed into water (left petri dish). This simulates cultivating a soil while it is wet. Note that strong dispersion has occurred within the surface soil as well as the subsoil. Again, no dispersion has taken place in the gypsum solution (right petri dish), even after remoulding.
Problems Caused by Dispersion Dispersion in a soil has the following consequences: Dispersed clay particles block soil pores resulting in restricted water and air movement. If surface soil pores are blocked by dispersed clay, the soil becomes massive and when dry may form a surface crust or hardsetting layer. This will inhibit seedling emergence and water penetration. Increased surface cloudiness can also occur after cultivation.
Surface crusting of a Sodosol. Crusting will result in reduced water infiltration as well as reduced plant emergence.
Cultivation of soils that are wet may lead to smearing and compaction at cultivation depth. Formation of a resultant cultivation pan could further reduce air, water and root movement into the subsoil. Soil aggregates may not disperse immediately after wetting but may do so if cultivated or trampled by stock in a wet condition. The dispersion test on remoulded soil simulates this condition. Subsoil dispersion results in reduced water movement down the profile. Following heavy rainfall, waterlogging of the surface soil could also result. The consequent lack of oxygen in the root zone will deleteriously affect the crop (Daniels et al., 1994). During hot weather, there may also be excessive evaporation due to the restriction of drainage through the profile. On sloping land, lateral water movement may occur above the relatively impermeable subsoil horizon.
Waterlogging caused by built up water on an impermeable sodic subsoil.
Subsoil dispersion also results in the structural breakdown of aggregates and increased soil density and hardness. Plant root movement will be restricted by the dense subsoil and much of the moisture and nutrients stored in the subsoil will not be used. Water and air movement will also be retarded. When wet dispersive soils have very little strength and are therefore more readily prone to gullying and tunnel erosion. Sodic clay subsoils are a major erosional problem if exposed or if the surface soil has been removed. DUPLEX PROFILE FORM: A Primary Profile Form of the Northcote Factual Key (1979) classification. It describes a soil where there is a sharp texture contrast between the A and B horizons. A duplex soil is often characterised by a sandy or loamy surface horizon with a sharp to clear boundary to a clay subsoil. Duplex soils are given the notation "D".
DURIPAN: Duripans are hard, subsurface horizons. They are cemented by silica or other materials such as iron oxides or calcium carbonate to the extent that fragments of the air-dry material will not slake after prolonged soaking in water or in Hydrochloric acid. They have a very firm or extremely firm consistence when moist and are always brittle, even after prolonged wetting (McDonald et al, 1990).
DYSTROPHIC: See base status.
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 8 of 27 EARTHS: A Great Soil Group (Stace et al., 1968) description defining a variable group of soils which are porous and sandy textured. They usually have an acidic trend (i.e. the pH decreases with depth), weak profile differentiation, diffuse horizon boundaries, an increase in clay content with depth and no A2 Horizon.
ELECTRICAL CONDUCTIVITY (EC): A measure of the conduction of electricity through water, or a soil water extract. The value can reflect the amount of soluble salts in a soil extract - therefore providing an indication of soil salinity. Saline soils are defined as those with an EC of greater than 1.5 dS/m for a 1:5 soil water extract and greater than 4 dS/m for a saturation extract. It can be interpreted in terms of the salinity tolerance of plants but soil texture needs to be considered in this interpretation.
ENDOACIDIC: Soils in which the major part of the profile deeper than 0.5 m is strongly acid. This term is used as a Subgroup distinction for Vertosols in the Australian Soil Classification (Isbell, 1996).
ENDOCALCAREOUS: A term used to describe a soil in which the major part of the profile deeper than 0.5 m is calcareous. This term is used as a Subgroup definition for the Vertosol Order in the Australian Soil Classification (Isbell, 1996).
ENDOHYPERSODIC: These soils deeper than a 0.5 m depth, have an ESP of 15 or more. This term is used as a Subgroup definition for Calcarosols and Vertosols in the Australian Soil Classification (Isbell, 1996).
EPIACIDIC: Soils in which the major part of the upper 0.5 m of the soil is strongly acid. This term is used as a Subgroup definition for Vertosols in the Australian Soil Classification (Isbell, 1996).
EPIBASIC: Epibasic is a term used in the Australian Soil Classification (Isbell, 1996) as a Subgroup descriptor for Calcarosols. It refers to Calcarosols that are not calcareous in the A1 or Ap horizon, or to a depth of 20 cm if the A1 horizon is only weakly developed.
EPICALCAREOUS: A soil in which the major part of the top 0.5 m of the profile is calcareous. It is used to describe Hydrosols and Vertosols in the Australian Soil Classification (Isbell, 1996).
EPIHYPERSODIC: Soils with at least one subhorizon within the top 0.5 m of the profile having an ESP greater than 15. Used as a Subgroup definition for Calcarosols and Vertosols in the Australian Soil Classification (Isbell, 1996).
EPIPEDAL: These soils have a pedal A Horizon, commonly blocky or polyhedral structure, with a moderate to strong grade and no surface crust. Used as a Great Group definition for Vertosols in the Australian Soil Classification (Isbell, 1996).
EPISODIC: These soils have an ESP of 6 or greater in the upper 0.1 m of the profile. This term is used as a Subgroup definition for Vertosols in the Australian Soil Classification (Isbell, 1996).
EXCHANGEABLE CALCIUM:MAGNESIUM RATIO (Exch. Ca:Mg): A ratio of exchangeable Calcium vs. exchangeable Magnesium in the soil. Soils with a low Ca:Mg ratio i.e. < 0.1 are considered to be Magnesic in the Australian Soil Classification (Isbell, 1996). A very low Ca:Mg ratio will in most cases indicate low exchangeable calcium levels (possible calcium deficiency for some plants).
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 9 of 27 EXCHANGEABLE SODIUM PERCENTAGE (ESP): Is calculated as the proportion of the cation exchange capacity occupied by the sodium ions and is expressed as a percentage. In Australia, sodic soils are categorised as soils with an ESP of 6-14% and strongly sodic soils have an ESP of 15% or greater.
EUTROPHIC: See base status.
FABRIC: Describes the appearance of the soil material (under a hand lens). Fabric differences are associated with the presence or absence of peds, the lustre of the ped surface and the presence, size and arrangement of pores in the soil mass (McDonald et al, 1990).
Fabric types include:
Earthy (or porous) (E): The soil material is coherent and characterised by the presence of pores with few if any peds. Soil particles are coated with oxides and/or clay particles are clumped around the pores.
Sandy (G): Soil material is coherent, with few if any peds. The soil mass appears as closely packed sand grains.
Rough-ped (R): Peds are evident and characteristically more than 50% of the peds are rough-faced, that is, they have relatively porous surfaces. They tend to have less clearly defined faces than smooth faced peds.
Smooth-ped (S): Peds are evident and more than 50% of them are dense and smooth faced, although the degree of lustre varies.
FACTUAL KEY: The Northcote Factual Key is a soil classification system that was developed by Keith Northcote in 1979. It is used to group Australian soils into recognisable Profile Forms. These are based on visible morphological properties (especially texture) and simple soil chemical properties and are labelled using an alphanumeric code (Northcote ,1979).
FERRIC HORIZON: A soil horizon containing more than 20% ferruginous nodules or concretions (also known as ironstone or buckshot) that are uncemented. The term is used as a definition for numerous Soil Orders in the Australian Soil Classification (Isbell, 1996). Ferric horizon (10-30 cm) within a Chromosol in the Corangamite region.
FERROSOLS: Soil Order of the Australian Soil Classification (Isbell, 1996). These soils lack strong texture contrast between the A and B horizons. The B2 horizon has structure more developed
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 10 of 27 than weak and a fine earth fraction which has a free iron oxide content greater than 5% (as opposed to a Dermosol).
FIELD CAPACITY (FIELD MOISTURE CAPACITY): The percentage of moisture remaining in a soil horizon 2-3 days after being saturated (by rainfall or irrigation) and after free drainage has ceased.
FLUVIAL: A geomorphic process whereby sediments are transported and deposited by flowing river water.
FLUVIATILE: Relates to fluvial.
FRAGIPAN: Fragipans are earthy pans that are usually loamy. They seem to be cemented, with hard to very hard consistence when dry and moderate to weak brittleness when moist. However, a dry fragment slakes or fractures when placed in water (McDonald et al, 1990).
FRIABLE: The term friable refers to a soil property of consistence describing the resistance of a material to deformation or rupture. Consistence refers to the degree of cohesion or adhesion of the soil mass and is strongly affected by the moisture content of the soil. The terms friable and very friable refer to the weak force or very weak force between thumb and forefinger required to just break or deform a 20 mm piece of soil in a moist condition
GILGAI MICRORELIEF: Gilgai’s are common where they are Grey Vertosol soils. The land surface is irregular with alternating mounds (puffs) and depressions (hollows) and is commonly referred to as ‘crab hole’ country.
Gilgai microrelief in a paddock in the Horsham region. Note the well defined mounds.
Gilgai microrelief is formed due to clay horizons shrinking and swelling with alternate drying and wetting cycles (vertic properties). This forces ‘blocks’ of subsoil material gradually upwards to form mounds. The resultant soil on the mounds have properties which are more like Grey Vertosol subsoils (i.e lighter colour, more alkaline, presence of carbonate, higher salinity).
Variation in a soil profile across gilgai microrelief. Note the variation in calcium carbonate and subsoil colour across the profile.
Continuous cultivation of gilgai paddocks results in the smoothing out of these formations. However, the forces that created them are still operating, as is evident by the displacement of fence posts. If the land is left undisturbed for a number of wetting and drying seasons they will reform. In areas with gilgai microrelief crop and pasture growth is likely to be uneven across a paddock. This is due to soil variations and poor drainage conditions in the depressions.
GLEYING: Gleying is indicative of permanent or periodic intense reduction due to wetness and is characterised by greying, bluish or greenish color, generally of low chroma. Mottling may be prominent as well as rusty root channel mottling.
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 11 of 27 GRADATIONAL PROFILE FORM: A Primary Profile Form of the Factual Key (Northcote, 1979). It describes a soil with a gradual increase in texture (i.e. becomes more clayey) as the profile deepens. Gradational soils are given the notation "G". Boundaries are usually gradual or diffuse.
GRANULAR STRUCTURE: Rounded peds that are porous, stable and less than 12 mm in diameter. Granular structure usually occurs in the surface horizons (McDonald et al, 1990).
GREAT SOIL GROUPS: A soil classification system developed by Stace et al. (1968). It is based on the description of soil properties such as colour, texture, structure, drainage, lime, iron, organic matter and salt accumulation, as well as on theories of soil formation. The profile is assigned to a Great Soil Group classification based on its description. The system is limited in that central concepts are inadequately defined making confident identification of some described profiles difficult. This system is no longer in regular use in Australia but some of the terms are still used quite frequently (e.g. Krasnozems) to describe soils.
GREY, BROWN AND RED CALCAREOUS SOILS: A Great Soil Group classification,(Stace et al., 1968). These soils are shallow, soft, powdery or weakly structured loams to light clays containing finely divided carbonates throughout the profile and showing very little horizon development. They tend to develop from highly calcareous rocks which underlie them, at depths up to 50 cm from the surface. Fragments of limestone may also be found in the profile. The surface texture may be a loam or a clay loam, with a weak platey or a fine blocky structure. Below this, the structure is massive or more clayey with a medium blocky structure of rough faced peds. The clay content tends to increase about one texture class throughout the profile.
GREY, BROWN AND RED CLAYS: A Great Soil Group Classification, Stace et al., (1968). This is a broad group of soils which have a moderate to very deep profile. These soils crack deeply on drying and have a high clay content throughout. Subsoil clays range from grey to brown or red in colour gradually becoming paler with increasing depth. In Victoria, these soils are typically alkaline throughout most of the profile and carbonates may also be present.
GYPSIC: These soils contain more than 20% visible gypsum with a minimum thickness of 0.1 m that is of apparent pedogenic origin. If the upper boundary of the horizon occurs below the 1 m depth it is disregarded in the classification. It is used as a definition for a number of Orders in the Australian Soil Classification (Isbell, 1996).
GYPSUM: A naturally occurring soft crystalline material which is a hydrated form of calcium sulphate. Deposits occur naturally in inland Australia. Gypsum contains approximately 23% calcium and 18% sulphur. It is used to improve soil structure and reduce crusting in hard setting clayey soils.
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 12 of 27 Soil Glossary H-R A-C | D-G | H-R | S-Z | References | Soil Homepage
H | I | J | K | L | M | N | O | P | Q | R
HAPLIC: A term used in the Australian Soil Classification (Isbell, 1996) which indicates that the major part of the upper 0.5 m of the soil profile is whole coloured. It is used as the lowest order Subgroup distinction for a number of Soil Orders. Note: by lowest order, it is meant that the soil described matches none of the other Subgroup classes e.g. a Haplic, Epipedal, black Vertosol is not acidic, sodic, calcareous etc.
HARDSETTING: The condition of a soil where the surface is dry, hard and compacted with no apparent pedal development. These soils are not disturbed or indented by pressure of the forefinger. These harder setting soils tend to result in high runoff.
HORIZONS: Soil layers within the profile which are reasonably homogeneous in terms of morphological characteristics and properties (e.g. colour, texture, and structure) to the layers above and below.
A soil profile usually has these basic layers:
A1 surface A2 subsurface B subsoil C substrate. HORIZON SUFFIXES: These are lower case letters or numbers used as further descriptors to the main horizons. The suffixes describe the genetic processes operating in the soil. For example, humus in the A1 horizon is indicated by A1h and calcium carbonate in the B2 horizon is indicated by B2k.
The horizon suffixes are as follows: See McDonald et al., 1990 for more detail. b - buried soil horizon (used in mineral soils only). c - iron, aluminium or manganese concretions or nodule accumulation. d - densipan (very fine sandy earthy pan). e - conspicuously bleached horizon. f - faunal accumulations e.g. worm casts, dominating A1 horizons. g - strong gleying. h - accumulation of amorphous organic matter where aluminium dominates over iron. j - sporadically bleached horizon. k - large accumulation of carbonates, commonly calcium carbonates. m - strong cementation. p - any disturbance by man e.g. ploughing. q - accumulation of secondary silica, qm is used for near continuous silica cementation. r - layers of weathered rock that can be dug with hand tools. s - an accumulation of sesquioxide organic matter where iron dominates over aluminium. t - accumulation of silicate clay. w - development of color and/or structure in the B Horizon with little or no accumulation of sesquioxide organic matter complexes.
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 13 of 27 x - fragipan or earthy pan. y - large accumulation of calcium sulphate (gypsum) in B Horizon. HUMIC: Where organic matter and aluminium compounds dominate under either semiaquic or aquic conditions. Subsoil horizons that are humic are notated as a Bh Horizon. This term is used as a Great Group definition for the Podosol Order in the Australian Soil Classification (Isbell, 1996).
HUMOSE: The relatively resistant, usually dark brown to black fraction of soil organic matter, peat or compost which forms as a result of biological decomposition of organic material.
Humose horizon (0-50 cm depth) of a Kurosol in the Corangamite region.
HUMOSE HORIZON: A humus rich surface or near surface horizon that is at least 20 cm thick and has an organic carbon content of more than 4% for sandy soils and greater than 6% for clayey soils. This term is used as a Subgroup distinction for a number of Soil Orders in the Australian Soil Classification (Isbell, 1996).
HUMOSESQUIC: Soils with only a Bhs Horizon within Aeric or Semiaquic conditions. This term is used as a Great Group definition for the Podosol Order in the Australian Soil Classification (Isbell, 1996).
HYDROSOLS: Soil Order of the Australian Soil Classification (Isbell, 1996). These are soils where a greater part of the profile is saturated for at least several months per year.
HYPERCALCIC: These soils have a Bk Horizon or a subsurface layer containing more than 20% soft, finely divided carbonate, less than 20% hard calcrete fragments and/or carbonate nodules, and/or carbonate coated gravel. The term is used as a definition for a number of Orders in the Australian Soil Classification (Isbell, 1996).
HYPERNATRIC: The major part of the upper 0.2 m of the B2 Horizon has an ESP greater than 25. This term is used as a Great Group definition for the Sodosol Order in the Australian Soil Classification (Isbell, 1996).
HYPOCALCIC: Soils where the carbonate in the B or B/C Horizon is evident only by using acid treatment, or is in the form of a few soft visible segregations with few if any hard nodules or concretions. This term is used as a definition for a number of soils in the Australian Soil Classification (Isbell, 1996).
ILLUVIATION: The process of deposition (in-washing) of soil materials either from suspension or solution, usually from an upper horizon into a lower soil horizon but also from a lateral source (Allaby, 1991).
INDURATED: Hardened soil particles (see Cemented).
INFILTRATION: The movement of water through the soil surface. Soils with a high infiltration capacity allow more rain to enter the soil than those with a low infiltration capacity. Runoff will
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 14 of 27 occur when the rate of rainfall exceeds the soil's infiltration capacity. Surface soil structure and texture are important determinants of the infiltration capacity of a soil.
INTRACTABLE: Tough consistence, hard to work.
KANDOSOLIC: A term used in the Australian Soil Classification (Isbell, 1996). to classify Hydrosols. This indicates that the soil would otherwise be classified as a Kandosol apart from the fact that it is saturated in the greater part of the profile for prolonged periods (i.e. 2-3 months) in most years - therefore making it a Hydrosol.
KANDOSOLS: A Soil Order of the Australian Soil Classification (Isbell, 1996). These soils lack strong texture contrast and have massive or only weakly structured B horizons. The B2 horizon is well developed and has a maximum clay content in some part of the B2 Horizon which exceeds 15%. They are also not calcareous throughout.
KRASNOZEM: A Great Soil Group (Stace et al.,1968). These soils are typically red, deep, well- structured, acid and porous soils. They have relatively high clay contents and tend to display a gradual increase in clay with depth.
KUROSOLS: A Soil Order of the Australian Soil Classification (Isbell, 1996). These soils have a clear or abrupt textural change at the A/B boundary. The upper B2 horizon is strongly acidic i.e. less than 5.5 in water.
KUROSOLIC: A Great Group description related to Hydrosols in the Australian Soil Classification. Refers to Hydrosols that have a clear or abrupt textural B horizon and the major part of the upper 20 cm of the B2 horizon is strongly acid.
LABILE: Loss of consistence, pieces break off the aggregate when it is dry and when it becomes moist the pieces stick back together.
LACUSTRINE: A geomorphic process whereby soil forming material is deposited in lakes.
LAND CAPABILITY: The ability of a piece of land to sustainably support a specific land use. It is an expression of the effect of the physical components of the land -especially the soil, but including climate - on determining whether a specific land use is likely to cause damage. If land is used beyond its capability, degradation results.
LATERITE: Refers to a soil profile with horizon/s rich in iron oxides. This is usually associated with deeply weathered profiles. The process whereby laterite is formed, is referred to as laterization. Laterization developed predominantly in the early Tertiary period when Australia experienced a warm, wet climate.
LATERITIC PODSOLIC: Great Soil Group Classification, (Stace et al., 1968). These soils are strongly leached with a strong texture contrast between thick sandy A horizons and mottled yellow- brown and red clay B horizons. Nodular pisolitic (secondary concretion generally of a greater length to width ratio e.g. bullet shape.) or massive ironstone occurs at the base of the bleached A2 horizon and in the upper B2 horizon. The pH trend is acid throughout the profile.
LEACHING: The removal in solution of soluble minerals and salts as water moves through the profile.
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 15 of 27 LENTICULAR STRUCTURE: Soil particles that are arranged around an elliptical or circular plane and are bounded by curved faces i.e. lens shaped. This structure often occurs in subsoils of Vertosols and can be associated with slickenside development.
LEVEE: A natural levee is a deposit of alluvium which is raised above the general level of the banks of a stream and its flood plain. Man-made levees may be constructed along the course of a river or stream in order to contain flood waters.
LIME: A naturally occurring calcareous material used to raise the pH of an acidic soil and/or supply calcium for plant growth. It is effective for treating acidic soils.
LITHIC: Refers to soils in which the B Horizon directly overlies hard rock. This term is used to describe Tenosols, Calcarosols, Organosols and Rudosols in the Australian Soil Classification (Isbell, 1996).
LITHOCALCIC: Describes soils with a calcareous horizon containing more than 50% of hard calcrete fragments and/or carbonate nodules or concretions and/or carbonate-coated gravel. It is used to describe Calcarosols, Chromosols, Dermosols, Kandosols and Sodosols using the Australian Soil Classification (Isbell, 1996).
LUNETTES: Crescent shaped aeolian deposits of fine sediment located on the eastern (or lee) side of lake beds or playas in semi-arid areas of southern Australia.
MAGNESIC: Soils with an exchangeable Ca/Mg ratio of less than 0.1 in the major part of the B2 Horizon. This term is used as a definition within a number of Soil Orders in the Australian Soil Classification (Isbell, 1996). These soils can often be strongly weathered.
MANGANIC: A horizon with a minimum thickness of 0.1 m that contains 20% or more (by weight or visual estimate) of black manganiferous nodules or concretions which are generally uncemented. Most nodules contain some iron. This term is used as a Subgroup definition for a number of Orders in the Australian Soil Classification (Isbell, 1996).
MASSIVE: This term applies to soil horizons greater than 6 mm in thickness, that appear to be coherent or solid and devoid of peds. When displaced, the soil separates into fragments which may be crushed into individual particles.
MELACIC: These soils are similar to Melanic but the pH (1:5 water) is less than 5.5 and there is no structure requirement. It is a subgroup of the Australian Soil Classification (Isbell, 1996).
MELANIC: These soils have either a dark coloured (i.e. Munsell (1992) colour value 3 or less and chroma 2 or less) surface or near surface horizon that has insufficient organic carbon to qualify as a humose horizon, with little or no evidence of stratification (layers). It is used as a Subgroup definition for a number of Orders in the Australian Soil Classification (Isbell, 1996).
MESONATRIC: In these soils, a major part of the upper 0.2 m of the B2 Horizon has an ESP between 15-25. Used as a Great Group definition for Sodosols in the Australian Soil Classification (Isbell, 1996).
MESOTROPHIC: See Base Status.
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 16 of 27 MOTTLING: The presence of more than one soil colour in a horizon. The soil may differ in colour either within peds or aggregates, or between them. Mottling occurs as blotches or streaks of subdominant colour throughout the main (i.e. matrix) colour. It does not refer to stains or coloured deposits on ped faces. Mottling is often an indication of poor profile drainage but may be caused by the weathering of parent material. Diffusely mottled implies that neighbouring colours are only slightly different.
MYCORRHIZAE: Means 'fungus root'. These are soil fungi that infect plant roots and produce a symbiotic relationship. The fungi acts as rootlets and increases the surface area available for contact with nutrients (particularly phosphorus and zinc) by ten fold. The mycorrhizae then makes these nutrients available to the plant. In exchange the plant gives back sugars to sustain the fungi, as it doesn't photosynthesis (Coyne, 1999). Fallowing, excessive tillage and soil fumigation can cause mycorrhizae to die out. Some plants such as rapeseed do not need mycorrhizae and therefore the mycorrhizae tends to die out of the soil. Plants growing with mycorrhizae are generally healthier and more resistant to root disease and root rot.
NATRIC: Soils where the major part of the upper 0.2 m of the B2 Horizon is sodic. Used as a Great Group definition for Hydrosols and Kurosols in the Australian Soil Classification (Isbell, 1996).
NORTHCOTE FACTUAL KEY: See Factual Key (Northcote, 1979).
NUTRIENT DEFICIENCY: Where the availability of an essential element is low and causes a reduction in plant growth, and interference with the life cycle of that plant.
Many soil factors are associated with low availability of nutrients. Usually it is due to low levels of the nutrient, but it may also be due to acidity influenced availability, low nutrient solubility, or immobilisation within organisms and organic matter.
NUTRIENT STATUS: Can be used as a rough guide to the availability of nutrients to plants. It is calculated as the sum of exchangeable calcium, magnesium and potassium (in milliequivalents per 100 g). The categories used are: very low (0 - 3.9); low (4 - 7.9); moderate (8 - 17.9); high (>18) (Lorimer and Rowan, 1982).
O HORIZONS: Horizons dominated by decomposing organic materials that have accumulated on the mineral soil surface (McDonald et al., 1990). This horizon is divided up into O1 and O2 horizons.
ORGANIC MATERIALS: Plant derived organic accumulations.
ORGANOSOLS: Soils that are dominantly made up of organic materials. A Soil Order of the Australian Soil Classification (Isbell, 1996).
ORTHIC: This term is used to describe Tenosols in the Australian Soil Classification (Isbell, 1996). It refers to soils with a B Horizon: that is weakly developed in terms of colour, structure, texture and segregations; or a B2 Horizon with less than 15% clay; or a transitional horizon (C/B) occurring in fissures in the parent rock or weathered rock.
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 17 of 27 OXYAQUIC: This term is used to describe Hydrosols in the Australian Soil Classification (Isbell, 1996). Soils with a seasonal or permanent water table where the major part of the solum (or the subsoil if the profile is layered) is whole coloured.
PANS: Hard or cemented layers interfering with air, water and root penetration.
PARAPANIC: A term used as a Subgroup definition for Podosols in the Australian Soil Classification (Isbell, 1996). It refers to soils with a strongly coherent (i.e. consistence 4-5) B Horizon e.g. Parapanic, Pipey, Semiaquic PODOSOL.
PARENT MATERIAL: The rock from which a soil profile develops.
PARNA: Is a fine textured calcareous deposit of aeolian origin. It is postulated to be derived from older soils and transported mostly in the form of small aggregates, during an earlier more arid period.
PARTICLE SIZE ANALYSIS: The measurement of the relative amounts of coarse sand, fine sand, silt and clay size particles in a soil sample (as determined in the laboratory). Also called 'mechanical analysis'.
Coarse sand 0.2 – 2 mm Fine Sand 0.02-0.2 mm Silt 0.002-0.02 mm Clay < 0.002 mm
Standard particle size classes used in Australia as per Marshall (1947). See chart and texture triangle in McDonald et al (1990) Soil and Land Survey Field Handbook 2nd Edition; pp116-117
PED: The natural unit of soil structure formed by the soil's tendency to fracture along planes of weakness.
PEDAL: A general soil science term indicating that soil structure is present. In the Australian Soil Classification (Isbell, 1996), pedal is used as a Great Group class for Calcarosols - where the subsoil (B) horizon has a grade of structure that is stronger than weak.
PEDOGENIC: Material formed by pedological processes (soil forming processes) exhibiting pedological features.
PETROCALCIC: Soils with a B Horizon that directly overlies a calcrete pan. This term is used as a Great Group or Subgroup distinction for a number of Soil Orders in the Australian Soil Classification (Isbell, 1996).
PETROFERRIC: These soils have ferruginous or ferromanganiferous nodules or concretions cemented into indurated blocks or large irregular fragments. Used as a Great Group definition for a number of Orders in the Australian Soil Classification (Isbell, 1996).
P HORIZONS: Commonly known as peat. These horizons, dominated by decomposing organic matter have accumulated under water or excessive wetness (McDonald et al., 1990). P Horizons are further divided into P1 and P2.
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 18 of 27 pH (SOIL): This is a measure of soil acidity and soil alkalinity on a scale of 0 (extremely acidic) to 14 (extremely alkaline). A pH of 7 is neutral. pH gives an indication of the availability of plant nutrients and relates to the growth requirements of particular crops. In most agricultural soils, pH is usually between 4 and 8.5. Excessive acidity or alkalinity makes the soils inhospitable for plant and microbial growth. Microorganisms don't flourish in low pH and enzyme activity also changes with the change in pH. Aluminium and Manganese solubility increases in acidic soils and becomes toxic to microorganisms (Coyne, 1999). Acid soils are usually deficient in necessary nutrients e.g. calcium and magnesium.
PIPEY (B HORIZON): These horizons are characterised by 'pipes' of bleached A2 horizon that penetrate (mostly vertically) into the B horizon. This results in a tongued A/B boundary on a profile face. The presence of a pipey horizon is used at the Great Group level within the Podosol Order of the Australian Soil Classification (Isbell, 1996), e.g. Parapanic, Pipey, Semiaquic PODOSOL.
PISOLITH: Rock particle 1-10 mm in diameter with an internal structure of concentric laminae (i.e. peel off).
PLANT AVAILABLE WATER CAPACITY (PAWC): The amount of soil water that can be extracted by the plant. It is defined as the difference in soil moisture content between the field capacity and the wilting point. It is expressed as millimetres of plant-available water within the root zone.
PLASTIC LIMIT: The water content of the soil above which the soil will compress and shear when compacted, leading to structural degradation occurring.
PLASTIC SOILS: A soil capable of being moulded or permanently deformed in shape without a change in volume, rebound or texture.
PLATY STRUCTURE: Peds are layered in plate-like sheets. This type of structure is usually associated with soils which have been subjected to compaction and is not normally associated with undisturbed soil profiles.
PLAYA: A large, shallow closed depression which is intermittently filled with water but is mainly dry due to evaporation. These are often former lake beds. A lunette will usually be present on the eastern margin of the playa.
PODOSOL: These soils have a B Horizon dominated by the accumulation of compounds of organic matter, aluminium and/or iron. These horizons may occur individually or in combination within a profile. A Soil Order of the Australian Soil Classification (Isbell, 1996).
Site SG9 Profile
The SG9 pit site is an example of a Podosol that has both a Bh and a Bhs horizon.
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 19 of 27 <-- 50-55 cm - Bh - dominated by organic compounds.
<-- 55-65 cm - Bhs - dominated by aluminium and organic compounds.
POLYHEDRAL STRUCTURE: A soil structural unit whereby soil particles are arranged around a point and bounded by more than six relatively flat but dissimilar faces.
POROSITY (SOIL): The degree of pore space in a soil i.e. the percentage of the total space between solid particles.
PRIOR STREAM: The course of a former stream responsible for the nearby sediments that did not carry water other than local drainage. A low ridge built up from materials deposited by stream flow along a former stream channel (McDonald et al., 1990).
Prior stream channel south of Tinamba in West Gippsland.
PRISMATIC STRUCTURE: A soil structural unit whereby soil particles are arranged around a vertical axis and bounded by relatively flat faces. The top of the prisms are also relatively flat. Prismatic structure is often associated with subsoil sodicity.
Prismatic structure in the subsoil (from 55 cm depth) of a Chromosol in the Corangamite region.
PROFILE: The vertical section of the soil from the soil surface down through the horizons including the parent material. It consists of two parts: the solum and the parent material.
RED-BROWN EARTHS: Great Soil Group Classification (Stace et al., 1968). The surface soil is moderately thick and mildly acid to neutral, and the B Horizons are usually alkaline and may contain carbonates. These soils are typical of semiarid to subhumid climates and develop on various parent materials.
The characteristic features of a red-brown earth include: an A horizon which is grey-brown to red-brown loamy sand to sandy clay loam; an A horizon which is weakly structured to massive; an abrupt to clear boundary between the A and B horizons; a B horizon with a brighter brown to red clay and a well developed medium prismatic to blocky structure. REDOXIC: These are soils with a seasonal or permanent water table where the major part of the solum is mottled. This term is used as a Suborder definition for Hydrosols in the Australian Soil Classification (Isbell, 1996).
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 20 of 27 RETICULATE MOTTLING: Soil horizons which have strongly developed reddish, yellowish, greyish or white mottling that forms a 'net' or 'mesh' type pattern. Reticulate Mottling.
RHYZOBIA: Rhyzobium is a genus of bacteria which can colonise root hairs on legumes and consequently provide nitrogen to the host plant by converting atmospheric nitrogen to a form subsequently useable by host.
The bacterial colonisation occurs in only some of the root hairs and nodules form as an outgrowth of the hairs.
The effectiveness of this relationship in providing a nitrogen supply to the host plant varies considerably.
R HORIZONS: These horizons contain continuous rock of a moderately strong to very strong nature such as bedrock (McDonald et al., 1990).
RUDOSOLS: These soils have limited pedological organisation as well as minimal development of the A1 horizon. A Soil Order of the Australian Soil Classification (Isbell, 1996).
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 21 of 27 Soil Glossary S-Z A-C | D-G | H-R | S-Z | References | Soil Homepage
S | T | U | V | W | X | Y | Z
SALINAS: Depressions holding salty groundwater that are often evaporative.
SALINITY: A measure of the total soluble salts in a soil. A saline soil is one with an accumulation of free salts at the soil surface and/or within the profile affecting plant growth and/or land use. It is generally attributed to changes in land use or natural changes in drainage or climate, which affects the movement of water through the landscape. Salinity levels of soil or water can be tested using Electrical Conductivity (EC).
SAPROLITE: Decomposed rock that has maintained characteristics that were present as an unweathered rock.
SEGREGATIONS: Accumulations of minerals in the soil due to the concentration of constituents. They occur as a result of chemical or biological action. They can develop in situ by either current or relict pedogenic processes (McDonald et al., 1990).
Segregations are described by their nature, abundance and form:
Nature: calcareous (carbonate), gypseous (gypsum), manganiferous (manganese) and ferromanganiferous (iron-manganese). Abundance: Very few <2% Few 2-10% Common 10-20% Many 20-50% Very many >50%
Form: C concretions Spheroidal formations (concentric in nature). N nodules Irregular rounded formations (not concentric or symmetric). Can have a hollow interior. F fragments Broken pieces of segregations. X crystals Single or complex clusters of visible crystals. S soft segregations Finely divided soft segregations. They contrast with surrounding soil in colour and composition but are not easily separated from the soil as separate bodies.
SELF-MULCHING: A structural condition of soils where there is a high degree of pedality. The peds naturally fall apart as the soil dries to form a loose surface mulch. Some Vertosols have self mulching surface soils.
A self-mulching surface soil of a Grey Vertosol near Horsham.
SEMIAQUIC: Soils with short term saturation in the B Horizon. This term is used as a definition for the Podosol Order in the Australian Soil Classification (Isbell, 1996).
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 22 of 27 SESQUIC: A sesquic B Horizon (or Bs Horizon) is where iron compounds are strongly dominant or codominant with aluminium and there is little evidence of organic matter. This term is used as a Great Group definition for the Podosol Order in the Australian Soil Classification (Isbell, 1996).
SESQUIOXIDE: An oxide containing 3 atoms of oxygen with 2 atoms of some other substance e.g. AL2O3.
SILICEOUS SANDS: These are a broad group varying in colour but are characterised by their uniform sand to clayey sand texture, deep profiles, massive single-grain structure and the absence of any distinct horizons except for a minimal accumulation of organic matter in the A1 horizon, making it slightly darker. This horizon can be absent when there is no vegetation to hold it in place.
SLAKING: The break down of soil aggregates when immersed in water into smaller sized micro- aggregates. These aggregates may subsequently disperse.
SLICKENSIDES: Subsoil structural features which develop as a result of two masses moving past each other, polishing and smoothing the surfaces. These are common in Vertosols.
Slickensides in a Vertosol from the Corangamite region.
SODICITY: Is a measure of exchangeable sodium in relation to other exchangeable cations. It is expressed as the Exchangeable Sodium Percentage (ESP). A sodic soil contains sufficient exchangeable sodium to interfere with the growth of plants, including crops. A soil with an ESP greater than 6 is generally regarded as being a sodic soil in Australia (Northcote and Skene, 1972). ESP levels are further classified in the Australian Soil Classification (Isbell, 1996). See Sodic Soils on the VRO website for more information.
SODICITY INDEX: There are three ratings for soil sodicity and they are as follows:
0-5 Non-sodic 5-15 Sodic 15 + Strongly Sodic
SODIUM ADSORPTION RATIO (SAR): The proportion of sodium in the adsorbed layer, which is held in the pore fluid of the clay. This identity is calculated from the soluble cations present in the supernatant liquid and is expressed as sodium [ calcium + magnesium ]½ 2
The SAR of a soil extract is generally preferred as a sodicity index rather than Exchangeable Sodium Percentage (ESP) because it is more easily determined (Mitchell, 1976). Also, ESP values can vary depending on whether Cation Exchange Capacity (CEC) or the sum of the major cations is used as the divisor.
SODOSOL: A Soil Order of the Australian Soil Classification (Isbell, 1996). These soils have a clear or abrupt textural change between the A Horizons and B Horizons. The top 20 cm of the B2 horizon is sodic and is not strongly acid. Soils with a subplastic B2 horizon are excluded.
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 23 of 27 SOIL FERTILITY: Soil fertility is defined by the Soil Science Society of America as "the status of a soil with respect to the amount and availability to plants of elements necessary for plant growth". The capacity of a soil to hold the major cations, Calcium, Magnesium, Potassium and Sodium (and Hydrogen, Aluminium and sometimes Manganese in acid soils) is widely used for agricultural assessment. It is a measure of the general fertility of the soil and is particularly important in irrigated soils, when cations would otherwise be leached out of the root zone (Soil Science Society of America, 1973), (Baker and Eldershaw, 1993).
SOIL TYPE: This is a basic unit for classifying and mapping soils. It groups soils where profiles vary within defined, narrow limits. A soil type developes from a common parent material and following the U.S. definition, has areas as well as depth.
SOLODIC SOIL: A Great Soil Group, (Stace et al., 1968) classification.These soils have a strong contrast between the texture of the A and B horizons and a bleached A2 horizon (which may contain a few sesquioxidic nodules). The A Horizons are usually acidic and the B Horizons are alkaline grading to strongly alkaline at depth. The B horizon has medium to coarse blocky peds (which may be arranged in a coarse columnar fashion). These soils are typical in semi-arid and subhumid climatic zones and tend to be very dense soils with low permeability. The difference between solodic soils and solodized solonetz soils occurs in the structure of the B horizon: solodics have a medium to coarse blocky structure whereas solodized solonetz soils have a coarse columnar structure with clearly defined domes on the tops of the columns.
SOLODISED SOLONETZ: A Great Soil Group (Stace et al., 1968) classification. These soils are identical to solodic soils except for the structure of the B Horizon. Solodics have a medium to coarse blocky structure where as solodized solonetz have a coarse columnar structure with clearly defined domes on the tops of the columns.
SOLONETZ: A Great Soil Group (Stace et al., 1968) classification. Typically, there is weak differentiation between the A Horizons. The A2 horizon may be sporadically bleached just above the clay subsoil. There is an abrupt boundary and a strong texture contrast between the A and B Horizons. Surface soils are typically neutral to alkaline with a strongly alkaline subsoil. The subsoil clays are high in sodium and magnesium ions and usually have a prismatic structure.
SOLONIZED BROWN SOILS: A Great Soil Group (Stace et al., 1968) classification. These soils have large amounts of calcium and magnesium carbonate in the profile. Soil properties show a gradual change down the profile. The most evident is the increase in carbonates with depth. Texture also becomes finer with depth and the pH changes from a neutral/slightly alkaline surface horizon to an alkaline subsoil. The soluble salt content of the subsoil also increases significantly. Dark manganiferous nodules can also occur in the subsoil.
SOLOTH: A Great Soil Group, (Stace et al., 1968) classification. Similar to a solodic soil but acidic throughout the profile. Tends to be a more typical soil of the humid regions where the exchangeable cations in the B Horizon of the solodised soils have been leached out.
SOLUM: A and B horizons that have developed from the parent material by the processes of soil formation.
STRUCTURE: Describes the way the soil particles are arranged to form soil peds. Peds are units of soil structure that are separated from each other by natural planes of weakness (McDonald et al., 1990). They differ from clods which are formed as a result of soil disturbance such as ploughing.
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 24 of 27 Structure is defined by three characteristics:
GRADE measures the degree of development and the distinctiveness of the peds. It varies depending on the soil water status and can be divided into five groups: single grain, loose and incoherent mass of individual particles; massive, when displaced the soil separates into fragments which may be crushed into ultimate particles; weak, peds indistinct; moderate, peds are well formed and visible but not distinct in undisplaced soil, adhesion between peds is usually firm and when displaced between one third and two thirds of the soil material consists of peds, and; strong, peds distinct in undisplaced soil, adhesion between peds is firm, and when displaced, two- thirds or more of the soil material consists of peds. SIZE is measured and described based on the average least dimension of the peds. A guideline is provided in the Australian Soil and Land Survey Field Handbook (McDonald et al., 1990) pages 126 to 131. TYPE of structure has been described throughout the glossary. For example, platy, prismatic, columnar, angular blocky, subangular blocky, polyhedral and lenticular.
A number of different grades and sizes of peds may occur within a horizon. This is referred to as compound pedality. An example of this is when prismatic structure breaks down into smaller blocky peds.
SUB-ANGULAR BLOCKY STRUCTURE: Similar to angular blocky except the peds are bound by six faces intersecting with round edges (i.e. like a rounded cube) (McDonald et al., 1990).
SUBNATRIC: In these soils a major part of the top 0.2 m of the B2 Horizon has an ESP between 6 and less than 15. These soils are considered to be sodic. Used as a Great Group definition for Sodosols in the Australian Soil Classification (Isbell 1996).
SUBPLASTIC: These soils have a consistence or textural property (after kneading for 1-2 minutes) that suggests less clay sized particles than the soil actually contains. A subplastic soil increases in field texture after 10 minutes of kneading i.e. the soil texture becomes more clayey and harder to work. It is a feature of relatively deep subsoils and much energy is required to break down the soil aggregates. Also, these soils do not shrink/swell greatly when wet (McDonald et al., 1990).
SUBSOIL: The B Horizon and its subdivisions, excludes the C Horizon.
SUBSOILing: Deep ploughing into the subsoil.
SUBSTRATE OBSERVATION TYPES:
P Soil pit E Existing vertical exposure C Relatively undisturbed soil core A Auger boring O Outcrop
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 25 of 27 SUPRACALCIC Term use to classify soils using the Australian Soil Classification (Isbell 1996). Refers to soils with a calcareous horizon containing 20-50% of hard calcrete fragments and/or carbonate nodules or concretions and/or carbonate-coated gravel.
SURFACE CRUST: A massive or weakly structured often lamina layer that is lighter in texture than the underlying pedal clay. This soil condition should not be confused with self-mulching behaviour (McDonald et al., 1990).
TENIC B HORIZONS: This horizon has a weakly developed B Horizon in comparison with the overlying A Horizon and other horizons below, in terms of texture, colour, structure and/or presence of segregations (including carbonate). This term is used in the Australian Soil Classification (Isbell, 1996).
TENOSOLS: Soil Order of the Australian Soil Classification (Isbell, 1996). These soils generally have weak pedological organisation throughout the profile apart from the A Horizon. Tenosols display more profile development than Rudosols and may include a weakly developed B Horizon with 15% clay or less.
TEXTURE (FIELD): Field texture is determined by measuring the behaviour of a small handful of soil grains (<2 mm in size) when moistened and kneaded (1-2 minutes) until it does not stick to the hand. It provides an estimate of the relative amounts of coarse sand, fine sand, silt and clay size particles. Soil texture influences many soil physical properties such as water holding capacity and hydraulic conductivity. Numerous soil properties affect the determination of texture such as type of clay minerals, organic matter, carbonates, etc. Texture is determined by the behaviour of the moist bolus and length of the ribbon when sheared between thumb and forefinger, as described by (McDonald et al., 1990).
TOTAL SOLUBLE SALTS (TSS): A measure of the soluble salts in the soil (mainly sodium chloride, sulphate and carbonate). It is a calculated value derived using the Electrical Conductivity (EC) reading where Total Soluble Salts % = Electrical Conductivity (dS/m) x 0.33. TSS needs to be considered relative to profile water movement.
TOXICITY: Refers to a harmful effect on a plant (or animal) from the alteration of an environmental factor. A toxicity will manifest as damage to an organisms and may lead to early death.
Most elements can be toxic to plants if present in large enough quantities in soil.
UNIFORM PROFILE FORM: A Primary Profile Form of the Northcote Factual Key Classification, (Northcote, 1979). These soil profiles have limited, if any texture change throughout the profile. There is generally no textural boundaries found within the uniform profile, except for possibly a surface crust. Uniform soils are given the notation "U".
VERTIC PROPERTIES: This term is used to describe a subsoil with a field texture of 35% or more clay that experiences significant shrinking and swelling, resulting from drying and wetting. This often results in the development of features such as surface cracking and gilgai formation. Evidence of vertic properties include the presence of slickensides and/or lenticular peds in the subsoil. The amount of swelling is dependent on the type of clay present. These features are of significant importance for engineering purposes such as road construction. This term is used as a Subgroup definition for a number of Soil Orders in the Australian Soil Classification (Isbell, 1996).
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 26 of 27 VERTOSOLS: A Soil Order of the Australian Soil Classification (Isbell, 1996). These are clay soils with shrink/swell properties that display strong cracks when dry and have slickensides and/or lenticular structural aggregates at depth.
VESICULAR: Blisters of burst bubbles under the crust of the soils surface Factual Key.
WATER REPELLENT: Soils that are fairly resistant to wetting (from a dry state). It is a condition usually associated with sandy surface horizons and is generally caused by an organic coating on sand grains.
WILTING POINT: The water content of the soil where the plant is no longer able to extract it and therefore the plant wilts (Cass, 1999). Wilting point is measured at approximately pF 4.2.
TAFE NSW – Western Sydney Institute 0cbe5ace382dff68e0244db4 Created: 15/09/2011 209580ee.doc Version: 1.0 Modified: 15/09/2011 Page 27 of 27