Managing Saline Fact Sheet No. 0.503 Crop Series| by T.A. Bauder, J.G. Davis, and R.M. Waskom* Salinity problems are caused from the Saline soils are found throughout Quick Facts accumulation of soluble salts in the root Colorado. These salts originate from the zone. These excess salts reduce plant growth natural weathering of minerals or from • Accumulation of salts in and vigor by altering water uptake and fossil salt deposits left from ancient sea irrigated soils is present in causing ion-specific toxicities or imbalances. beds. Salts accumulate in the soil of arid most irrigated regions of Establishing good is generally the climates as water or Colorado. cure for these problems, but salinity problems seepage evaporates, leaving minerals behind. are often more complex. Proper management Irrigation water often contains salts picked • Crop losses may occur with procedures, combined with periodic soil tests, up as water moves across the landscape or irrigation water containing as are needed to prolong the productivity of salt- are found naturally in groundwater. Salts little as 700 to 850 mg/L TDS affected soils. also may come from human-induced sources (total dissolved solids) or This fact sheet describes techniques for such as municipal runoff or water treatment. EC>1.2 dS/m. managing saline soils. Management for sodic A detailed description of how irrigation soils may differ and is described in fact sheet water quality affects crop production and • Salt-affected soils may inhibit 0.504, Managing Sodic Soils. You also may contributes to is found in fact seed germination, retard want to review fact sheet 0.521, Diagnosing sheet 0.506, Irrigation Water Quality Criteria. plant growth, and cause Saline and Sodic Soil Problems to determine irrigation difficulties. if you have a saline soil, sodic soil or perhaps • Saline soils cannot be another problem in your field. Measuring Soil Salinity Salinity is measured by passing an reclaimed by chemical electrical current through a soil solution amendments, conditioners or Salt Sources extracted from a saturated soil sample. The fertilizers. Saline soils contain large amounts of water ability of the solution to carry a current is • Saline soils are often soluble salts that inhibit seed germination called electrical conductivity (EC). EC is reclaimed by salts and plant growth. The salts are white, measured in deciSiemens per meter (dS/m), from the plant root zone. chemically neutral, and include chlorides, which is the numerical equivalent to the sulfates, carbonates and sometimes nitrates of old measure of millimhos per centimeter calcium, magnesium, sodium and potassium (Table 2). The lower the salt content of the (Table 1). soil, the lower the dS/m rating and the less

Table 1: Common salt compounds. Salts are ionic crystalline compounds consisting of a cation and an anion. Salt compound Cation (+) Anion (-) Common name NaCl sodium chloride halite (table salt)

Na2SO4 sodium sulfate Glauber’s salt

MgSO4 magnesium sulfate epsom salts

NaHCO3 sodium bicarbonate baking soda

Na2CO3 sodium carbonate sal soda

CaSO4 calcium sulfate gypsum CaCO calcium carbonate calcite (lime) 3 ©Colorado State University Extension. 7/03. Revised 10/14. *T.A. Bauder, Extension water quality specialist; J. Davis, www.ext.colostate.edu Colorado State University Extension soils specialist and professor, soil and crop sciences; and R.M. Waskom, director, Colorado Water Institute & CSU Water Center. 10/2014 Table 2: Terms, units and conversions. a level of 2 to 4 dS/m affects some crops. harmful. This third method is called Symbol Meaning Units Levels of 4 to 5 dS/m affect many crops and managed accumulation­ . above 8 dS/m affect all but the very tolerant Total Salinity crops (Table 3). a TDS Total mg/L Although several treatments and Leaching Requirement dissolved b ppm management practices can reduce salt levels For most surface irrigation systems solids in the soil, there are some situations where in Colorado (furrow and flood), c EC Electrical dS/m it is either impossible or too costly to attain irrigation inefficiency (or over-irrigation) d conductivity mmho/cm desirably low soil salinity levels. In some generally is adequate to satisfy the e μmho/cm cases, the only viable management option is leaching requirement. However, poor Conversions to plant salt-tolerant crops. Sensitive crops, irrigation uniformity often results in salt 1 dS/m = 1 mmho/cm = 1000 μmho/cm such as pinto beans, cannot be managed accumulation in parts of a field or bed. 1 mg/L = 1 ppm profitably in saline soils. Table 3 shows Surface irrigators should compare leaching amg/L = milligrams per liter the relative salt tolerance of field, forage, requirement values to measurements bppm = parts per million and vegetable crops. The table shows the of irrigation efficiency to determine cdS/m = deciSiemens per meter at 25° C approximate soil salt content (expressed if additional irrigation is needed. dmmho/cm = millimhos per centimeter at as the electrical conductivity of a saturated Adding more water to satisfy a leaching 25° C paste extract (ECe) in dS/m at 25 degrees C) requirement reduces irrigation efficiency eμmho/cm = micromhos per centimeter at where 0, 10, 25, and 50 percent yield and may result in the loss of nutrients or 25° C decreases may be expected. Actual yield pesticides and further dissolution of salts reductions will vary depending upon the from the soil profile. crop variety and the climatic conditions Leaching is accomplished on a limited the effect on plant growth. Soil samples during the growing season. basis at key times during the growing taken for soil fertility purposes are adequate Fruit crops may show greater yield season, particularly when a grower may for looking for trends in salinity, but may variation because a large number of have high quality water available. Surface not provide the same information as rootstocks and varieties are available. Also, water in most areas of the state tends to sampling targeted for diagnosing salinity. stage of plant growth has a bearing on salt have lower salinity than shallow, alluvial Refer to 0.521, Diagnosing Saline and Sodic tolerance. Plants are usually most sensitive groundwater. Deep groundwater may have Soil Problems for more detail on assessing to salt during the emergence and early an even lower salinity than either shallow saline soil conditions. seedling stages. Tolerance usually increases groundwater or surface water. In situations Soil salinity can also be measured in as the crop develops. where a grower has multiple water sources the field with electromagnetic conductivity The salt tolerance values apply only of varying quality, consider planned meters. This technology works through from the late seedling stage through leaching events at key salinity stress periods the use of a transmitting coil that induces a maturity, during the period of most rapid for a given crop. magnetic field into the soil. A receiving coil plant growth. Crops in each class are Most crops are highly sensitive to reads induced currents in the soil. Typically generally ranked in order of decreasing salinity stress in the germination and this instrument is towed or dragged behind salt tolerance. seedling stages. Once the crop grows past an ATV and will take readings while these stages, it can often tolerate and grow driving in a pattern across the field. When well in higher salinity conditions. Planned combined with GPS technology, a map Treatment of Saline Soil periodic leaching events might include of salinity levels can be produced to show Saline soils cannot be reclaimed by a post-harvest irrigation to push salts relative levels of salinity within a field. chemical amendments, conditioners or below the root zone to prepare the soil To compare to published salinity values, fertilizers. A field can only be reclaimed (especially the seedbed/surface zone) for soil samples are required to calibrate the by removing salts from the plant root the following spring. Fall is the best time instrument to soil salinity levels in saturated zone. In some cases, selecting salt-tolerant for a large, planned leaching event because soil pastes described above. Some USDA- crops may be needed in addition to nutrients have been drawn down. However, Natural Resources Conservation Service managing soils. since each case is site-specific, examine (NRCS) offices and several commercial There are three ways to manage saline the condition of the soil, groundwater, entities offer this service in Colorado. soils. First, salts can be moved below the drainage, and irrigation system for a root zone by applying more water than given field before developing a sound Crop Tolerance to Soil Salinity the plant needs. This method is called the leaching plan. leaching requirement method. The second Sprinkler-irrigated fields with poor Excessive soil salinity reduces the method, where soil moisture conditions water quality present a challenge because it yield of many crops. This ranges from a dictate, combines the leaching requirement is difficult to apply enough water to leach slight crop loss to complete crop failure, method with artificial drainage. Third, the salts and you cannot effectively utilize depending on the type of crop and the salts can be moved away from the root row or bed configurations to manage severity of the salinity problem. Yields of zone to locations in the soil, other than accumulation. Growers should monitor the most crops are not significantly affected below the root zone, where they are not soil EC and irrigation water salinity. Where where salt levels are 0 to 2 dS/m. Generally, adequate irrigation water exists above With all artificial drainage systems you zones of salt accumulation stay away crop requirements, a leaching fraction (or must also consider disposal of the drainage from germinating seeds and plant roots. percent of additional water needed above water. Restrictions on the discharge of Irrigation uniformity is essential with this crop requirements) can be calculated using drain water to streams may apply in certain method. Without uniform distribution of this equation: situations and should be investigated water, salts will build up in areas where through the Colorado Department of the germinating seeds and seedling plants ECw LR = Public Health and Environment. In the will experience growth reduction and 5 ECe - ECw case of regulated discharge, treatment or possibly death. collection and evaporation of the water Double-row bed systems require on site may be required and may add uniform wetting toward the middle of the where: LR = the minimum leaching requirement needed to significant costs. bed. This leaves the sides and shoulders of control salts within the The advantage of artificial drainage the bed relatively free from injurious levels tolerance (ECe) of the crop with ordinary surface methods is that it provides the ability to use high of salinity. Without uniform applications of irrigation (Table 4) quality, low salinity irrigation water (if of water (one furrow receiving more or EC = salinity of the applied w irrigation water in dS/m available to a grower) to completely remove less than another), salts accumulate closer salts from the soil. However, artificial to one side of the bed. Periodic leaching EC = average soil salinity tolerated e by the crop as measured drainage systems will not work where there of salts down from the soil surface and on a soil saturation extract (Table 4). It is recommended is no saturated condition in the soil. Water below the root zone may still be required

that the ECe value that can be expected to result in at least a will not collect in a drain if the soil around to ensure the beds are not eventually 90 percent or greater yield be it is not saturated. salted out. used in the calculation. After drainage appears adequate, the Alternate furrow irrigation may be leaching process can begin. The following desired for single-row bed systems. This The total annual depth of water that equations can be used to estimate how is accomplished by irrigating every other needs to be applied to meet both the crop much water is required to leach salts for furrow and leaving alternating furrows dry. demand and leaching requirement can be reclamation purposes. Salts are pushed across the bed from the estimated from equation. irrigated side of the furrow to the dry side. D = (k x D x EC ) / EC (1) Care is needed to ensure enough water is ET w s ei ef AW = applied to wet all the way across the bed 1 - LR depth of water infiltrated to prevent build up in the planted area. where: DW = This method of salinity management can where: AW = depth of applied water D = depth of soil to be (in year) s reclaimed still result in plant injury if large amounts

total annual crop water of natural rainfall fill the normally dry ET = 0.30 for fine-textured soils, demand (in year) k = 0.10 for coarse-textured soils furrows and push salts back across the LR = leaching requirement bed toward the plants. This phenomenon expressed as a fraction EC = initial soil salinity of soil profile (leaching fraction) ei also occurs if the normally dry furrows are

final soil salinity desired accidentally irrigated. ECef = Leaching every year may be eliminated by growing salt sensitive crops early in the This equation can be used to estimate Other Management Options crop rotation following leaching. As salt the depth of water to apply for simple accumulates, more salt-tolerant crops are Residue Management continuous ponding with one application grown. Leaching is performed following Crop residue at the soil surface of water. When intermittent ponding or the last crop in the rotation. Crop rotation reduces evaporative water losses, thereby sprinkler irrigation is used, k = 0.1 for all example are: limiting the upward movement of salt soils. With intermittent ponding, several • pinto beans, corn, wheat, and barley (from shallow, saline groundwater) into small applications are applied. Using several • onions, cantaloupe, and sorghum. the root zone. Evaporation and thus, salt small applications requires less water than accumulation, tends to be greater in bare one single application. See the UC Davis soils. Fields need to have 30 percent to publication cited below for additional Leaching Plus Artificial 50 percent residue cover to significantly guidelines on using this equation for Drainage reduce evaporation. Under crop residue, reclamation leaching. Where shallow water tables limit the soils remain wetter, allowing fall or winter use of leaching, artificial drainage may precipitation to be more effective in be needed. Cut drainage ditches in fields Managed Accumulation leaching salts, particularly from the surface soil layers where damage to crop seedlings below the level to channel away In addition to leaching salt below is most likely to occur. drainage water and allow the salts to leach the root zone, salts can also be moved to Plastic mulches used with out. Drainage tile or plastic drainpipe can areas away from the primary root zone effectively reduce salt concentration from also be buried in fields for this purpose. with certain crop bedding and surface evaporation. Sub-surface drip irrigation Proper design and construction of a irrigation systems. Figures 1 and 2 illustrate pushes salts to the edge of the soil wetting drainage system is critical and should be several ways to manage salt accumulation front, reducing harmful effects on seedlings performed by a trained professional, such in this manner. The goal is to ensure the as your local USDA-NRCS. and plant roots. Summary Under irrigated conditions in arid and semi-arid climates, the build-up of salinity in soils is inevitable. The severity and rapidity of build-up depends on a number of interacting factors such as the amount Good uniformity: salts accumulate in the center of the bed and away from plants. of dissolved salt in the irrigation water and the local climate. However, with proper management of soil moisture, irrigation system uniformity and efficiency, local drainage, and the right choice of crops, soil salinity can be managed to prolong field productivity.

Poor uniformity: salts accumulate toward edge of bed near one row. References Figure 1. Salt management in double-row bed system. Ayers, R.S. and D.W. Westcot. 1994. Water Quality for Agriculture. FAO Irrigation and Drainage Paper 29, Rev 1. ISBN 92-5-102263-1 Hanson, B.R., S.R. Grattan and A. Fulton. 2006. Agricultural Salinity and Drainage. UC Davis Publication 3375. Tanji, K.K. 1990. “Nature and extent of agricultural salinity,” In: Agricultural Salinity Assessment and Management, Uniform, healthy plants with alternate furrow irrigation (salt accumulates in the dry furrows). ed. K.K. Tanji. American Society of Civil Engineers Manuals and Reports on Engineering Practice No. 71. ASCE.

Irregular growth due to variable accumulation of salt (plants may overcome this situation if roots can grow out of the saline area).

Figure 2. Salt management in single-row bed systems.

Pre-plant Irrigation Keeping soil moisture levels higher between As mentioned before, most crop plants irrigation events effectively dilutes salt are more susceptible to salt injury during concentrations in the root zone, thereby germination or in the early seedling stages. reducing the salinity hazard. An early-season application of good quality Most surface irrigation systems (flood water, designed to fill the root zone and or furrow systems) cannot be controlled leach salts from the upper 6 to 12 inches of to apply less than 3 or 4 inches of water soil, may provide good enough conditions per application and are not generally for the crop to grow through its most suited to this method of salinity control. injury-prone stages. Sprinkler systems, particularly center-pivot and linear-move systems configured with Irrigation Frequency Management low energy precision application (LEPA) nozzle packages or properly spaced drop Salts are most efficiently leached from nozzles, and drip irrigation systems provide the soil profile under higher frequency the best control to allow this type of irrigation (shorter irrigation intervals). salinity management. Table 3: Potential yield reduction from saline soils for selected crops. Relative yield decrease % 0 10 25 50

Field crops (ECe) Barley 8.0 10.0 13.0 18.0 Sugarbeets* 7.0 8.7 11.0 15.0 Wheat 6.0 7.4 9.5 13.0 Sorghum 4.0 5.1 7.2 11.0 Soybean 5.0 5.5 6.2 7.5 Corn 1.7 2.5 3.8 5.9 Bean 1.0 1.5 2.3 3.6 Forages Tall wheatgrass 7.5 9.9 13.3 19.4 Wheatgrass 7.5 9.0 11.0 15.0 Crested wheatgrass 3.5 6.0 9.8 16.0 Tall fescue 3.9 5.8 8.6 13.3 Orchardgrass 1.5 3.1 5.5 9.6 Alfalfa 2.0 3.4 5.4 8.8 Meadow foxtail 1.5 2.5 4.1 6.7 Cloveralsike, red, ladino, 1.5 2.3 3.6 5.7 strawberry Bluegrass and other turf ** Vegetables Broccoli 2.8 3.9 5.5 8.2 Cucumber 2.5 3.3 4.4 6.3 Cantaloupe 2.2 3.6 5.7 9.1 Spinach 2.0 3.3 5.3 8.6 Cabbage 1.8 2.8 4.4 7.0 Potato 1.7 2.5 3.8 5.9 Sweet corn 1.7 2.5 3.8 5.9 Lettuce 1.3 2.1 3.2 5.2 Onion 1.2 1.8 2.8 4.3 Carrot 1.0 1.7 2.8 4.6 *Sensitive during germination and emergence, ECe should not exceed 3dS/m at this time. Excerpted from R. S. Ayers and D.W. Westcot, 1976, Water Quality for Agriculture, Irrigation and Drainage Paper 29, FAO, Rome. Crop salt tolerance data in the table were developed, almost entirely, by the U.S. Salinity Laboratory, Riverside, CA. **For specifics on turfgrass species, see Colorado State University Extension fact sheet 7.227, Growing Turf on Salt-Affected Sites.

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