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Home , Saline water, Salinity, Surface irrigation, Total dissolved solids

B-1667 4-03

Irrigation Quality Standards and Management Strategies Standards and Salinity Management

Guy Fipps*

Nearly all contain dis - Generally, “” is thought of as Water Analysis: solved and trace elements, ordinary table salt ( chlo - many of which result from the ride). How-ever, many types of Units, Terms and natural of the ’s salts exist and are commonly Sampling surface. In addition, found in Texas waters (Table 1). waters from irrigated lands and Most salinity problems in agricul - Numerous parameters are used to effluent from city and ture result directly from the salts define irrigation water quality, to industrial waste water can impact carried in the irrigation water. assess salinity hazards, and to water quality. In most irrigation The process at work is illustrated determine appropriate management situations, the primary water qual - in Figure 1, which shows a strategies. A complete water quali - ity concern is salinity levels, since beaker of water containing a salt ty analysis will include the deter - salts can affect both the struc - of 1 percent. As mination of: ture and crop yield. However, a water evaporates, the dissolved number of trace elements are salts remain, resulting in a solu - 1) the total concentration of solu - found in water which can limit its tion with a higher concentration ble salts, use for irrigation. of salt. The same process occurs 2) the relative proportion of sodi - in . Salts as well as other dis - um to the other cations, solved substances begin to accu - 3) the concentration as *Associate Professor and Extension mulate as water evaporates from Agricultural Engineer, Department of related to the concentration of Agricultural Engineering, The Texas A&M the surface and as crops withdraw and magnesium, and System, College Station, Texas 77843-2117. water.

Table 1. Kinds of salts normally found in irrigation waters, with chemical symbols and approxi- mate proportions of each salt. 1 (Longenecker and Lyerly, 1994) Chemical name Chemical symbol Approximate proportion of total salt content NaCl Moderate to large

Sodium sulfate Na 2SO 4 Moderate to large Calcium chloride CaCl 2 Moderate Calcium sulfate (gypsum) CaSO 4 2H 2O Moderate to small Magnesium chloride MgCl 2 Moderate MgS0 4 Moderate to small chloride KCl Small

Potassium sulfate K2SO 4 Small NaHCO 3 Small Calcium CaCO 3 Very Small Sodium carbonate Na 2CO 3 Trace to none Borates BO -3 Trace to none NO -3 Small to none 1Waters vary greatly in amounts and kinds of dissolved salts. This water typifies many used for irrigation in Texas.

3 Figure 1. Effect of water evaporation on the concentration of salts in . A liter is 1.057 quarts. Ten grams is .035 ounces or about 1 teaspoonful.

4) the of specific Two Types of Salt the TDS () or elements and compounds. Problems the EC (electric conductivity). The amounts and combinations of TDS is sometimes referred to as these substances define the suit - the total salinity and is measured ability of water for irrigation and Two types of salt problems exist or expressed in parts per million the potential for toxicity. which are very different: those (ppm) or in the equivalent units of Table 2 defines common parame - associated with the total salinity milligrams per liter (mg/L). and those associated with sodium. ters for analyzing the suitability of EC is actually a measurement of Soils may be affected only by water for irrigation and provides electric current and is reported in salinity or by a combination of some useful conversions. one of three possible units as both salinity and sodium. When taking water samples for given in Table 2. Subscripts are laboratory analysis, keep in mind Salinity Hazard used with the symbol EC to iden - that water from the same source tify the source of the sample. can vary in quality with time. Water with high salinity is toxic EC iw is the electric conductivity Therefore, samples should be test - to and poses a salinity haz - of the irrigation water. EC e is the ed at intervals throughout the ard . Soils with high levels of electric conductivity of the soil as year, particularly during the total salinity are call saline soils . measured in a soil sample (satu - potential irrigation period. The High concentrations of salt in the rated extract) taken from the root Soil and Water Testing Lab at soil can result in a “physiologi - zone. EC d is the of Texas A&M University can do a cal” drought condition. That is, the saturated extract taken from complete salinity analysis of irri - even though the field appears to below the root zone. EC d is used gation water and soil samples, and have plenty of moisture, the to determine the salinity of the will provide a detailed computer plants wilt because the roots are drainage water which leaches printout on the interpretation of unable to absorb the water. Water below the root zone. the results. Contact your county salinity is usually measured by Extension agent for forms and information or contact the Lab at Types of Salinity Problems (979) 845-4816. affects can lead to salinity plants saline soil hazard condition

affects can lead to sodium soils sodic soil condition

4 Table 2. Terms, units, and useful conversions for understanding ingly impervious to water pene - water quality analysis reports. tration. Fine textured soils, espe - cially those high in clay, are most Symbol Meaning Units subject to this action. Certain Total Salinity amendments may be required to a. EC electric conductivity mmhos/cm maintain soils under high SARs. µmhos/cm Calcium and magnesium, if pre - dS/m sent in the soil in large enough b. TDS total dissolved solids mg/L quantities, will counter the effects ppm of the sodium and help maintain Sodium Hazard good soil properties. a. SAR sodium adsorption ratio — Soluble sodium per cent (SSP) is b. ESP exchangeable sodium percentage — also used to evaluate sodium haz - ard. SSP is defined as the ration Determination Symbol Unit of measure Atomic weight of sodium in epm (equivalents per Constituents million) to the total cation epm (1) cations 3 multiplied by 100. A water with a calcium Ca mol/m 40.1 SSP greater than 60 per cent may magnesium Mg mol/m 3 24.3 3 result in sodium accumulations sodium Na mol/m 23.0 that will cause a breakdown in the potassium K mol/m 3 39.1 soil’s physical properties. (2) anions bicarbonate HCO mol/m 3 61.0 3 3 , Trace Elements sulphate SO 4 mol/m 96.1 chloride Cl mol/m 3 35.5 and Other Problems 3 carbonate CO 3 mol/m 60.0 NO mg/L 62.0 A number of other substances 3 may be found in irrigation water Trace Elements and can cause toxic reactions in boron B mg/L 10.8 plants (Table 3). After sodium, Conversions chloride and boron are of most 1 dS/m = 1 mmhos/cm = 1000 µmhos/cm concern. In certain areas of Texas, 1 mg/L = 1 ppm boron concentrations are exces - TDS (mg/L) ≈ EC (dS/m) x 640 for EC < 5 dS/m sively high and render water TDS (mg/L ≈ EC (dS/m) x 800 for EC > 5 dS/m unsuitable for . Boron TDS (lbs/ac-ft) ≈ TDS (mg/L) x 2.72 can also accumulate in the soil. Concentration (ppm) = Concentration (mol/m3) times the atomic weight Crops grown on soils having an Sum of cations/anions imbalance of calcium and magne - (meq/L) ≈ EC (dS/m) x 10 sium may also exhibit toxic Key symptoms. Sulfate salts affect mg/L = milligrams per liter sensitive crops by limiting the ppm = parts per million uptake of calcium and increasing dS/m = deci Siemens per meter at 25° C the adsorption of sodium and potassium, resulting in a distur - Sodium Hazard effects of sodium. For waters con - bance in the cationic balance taining significant amounts of within the plant. The bicarbonate Irrigation water containing large bicarbonate, the adjusted sodium in soil solution harms the amounts of sodium is of special adsorption ratio (SAR adj ) is some - mineral nutrition of the plant concern due to sodium’s effects times used. through its effects on the uptake on the soil and poses a sodium Continued use of water having a and metabolism of . High hazard . Sodium hazard is usually concentrations of potassium may expressed in terms of SAR or the high SAR leads to a breakdown in the physical structure of the introduce a magnesium deficiency sodium adsorption ratio . SAR is and iron chlorosis. An imbalance calculated from the ratio of sodi - soil. Sodium is adsorbed and becomes attached to soil particles. of magnesium and potassium may um to calcium and magnesium. be toxic, but the effects of both The latter two ions are important The soil then becomes hard and compact when dry and increas - can be reduced by high calcium since they tend to counter the levels.

5 Table 3. Recommended limits for constituents in for irrigation. (Adapted from Rowe and Abdel-Magid, 1995) Constituent Long-term Short-term Remarks use (mg/L) use (mg/L) Aluminum (Al) 5.0 20 Can cause nonproductivity in acid soils, but soils at pH 5.5 to 8.0 will precipitate the ion and eliminate toxicity. Arsenic (As) 0.10 2.0 Toxicity to plants varies widely, ranging from 12 mg/L for Sudan grass to less than 0.05 mg/L for . Beryllium (Be) 0.10 0.5 Toxicity to plants varies widely, ranging from 5 mg/L for kale to 0.5 mg/L for bush beans. Boron (B) 0.75 2.0 Essential to plant growth, with optimum yields for many obtained at a few-tenths mg/L in . Toxic to many sensitive plants (e.g., citrus) at 1 mg/L. Most grasses relatively tolerant at 2.0 to 10 mg/L. Cadmium (Cd) 0.01 0.05 Toxic to beans, beets, and turnips at concentrations as low as 0.1 mg/L in nutrient solution. Conservative limits recommended. Chromium (Cr) 0.1 1.0 Not generally recognized as essential growth element. Conservative limits recommended due to lack of knowledge on toxicity to plants. Cobalt (Co) 0.05 5.0 Toxic to tomato plants at 0.1 mg/L in nutrient solution. Tends to be inactivated by neutral and alkaline soils. Copper (Cu) 0.2 5.0 Toxic to a number of plants at 0.1 to 1.0 mg/L in nutrient solution. Fluoride (F –) 1.0 15.0 Inactivated by neutral and alkaline soils. Iron (Fe) 5.0 20.0 Not toxic to plants in aerated soils, but can contribute to soil acidifi- cation and loss of essential phosphorus and molybdenum. Lead (Pb) 5.0 10.0 Can inhibit plant cell growth at very high concentrations. Lithium (Li) 2.5 2.5 Tolerated by most crops at up to 5 mg/L; mobile in soil. Toxic to citrus at low doses recommended limit is 0.075 mg/L. Manganese (Mg) 0.2 10.0 Toxic to a number of crops at a few-tenths to a few mg/L in acid soils. Molybdenum (Mo) 0.01 0.05 Nontoxic to plants at normal concentrations in soil and water. Can be toxic to livestock if forage is grown in soils with high levels of available molybdenum. Nickel (Ni) 0.2 2.0 Toxic to a number of plants at 0.5 to 1.0 mg/L; reduced toxicity at neutral or alkaline pH. Selenium (Se) 0.02 0.02 Toxic to plants at low concentrations and to livestock if forage is grown in soils with low levels of added selenium. Vanadium (V) 0.1 1.0 Toxic to many plants at relatively low concentrations. Zinc (Zn) 2.0 10.0 Toxic to many plants at widely varying concentrations; reduced toxicity at increased pH (6 or above) and in fine-textured or organic soils.

6 Classification of Table 6. Classification of salt-affected soils based on analysis of Irrigation Water saturation extracts. (Adapted from James et al., 1982) Criteria Normal Saline Sodic Saline-Sodic

Several different measurements are EC e (mmhos/cm) <4 >4 <4 >4 used to classify the suitability of SAR <13 <13 >13 >13 water for irrigation, including EC iw , the total dissolved solids, and SAR. Some permissible limits and the salt streaks along the fur - Water Quality for classes of irrigation water are rows. The compounds which given in Table 4. In Table 5, the cause saline soils are very soluble Effects on Plants sodium hazard of water is ranked in water; therefore, is and Crop Yield from low to very high based on usually quite effective in reclaim - SAR values. ing these soils. Table 7 gives the expected yield Sodic soils (resulting from sodi - reduction of some crops for vari - Classification of um hazard) generally have a pH ous levels of soil salinity as mea - Salt-Affected Soils value between 8.5 and 10. These sured by EC under normal grow - soils are called “black alkali ing conditions, and Table 8 gives soils” due to their darkened potential yield reduction due to Both EC and SAR are commonly e appearance and smooth, slick water salinity levels. Generally used to classify salt-affected soils looking areas caused by the dis - forage crops are the most resistant (Table 6). Saline soils (resulting persed condition. In sodic soils, to salinity, followed by field from salinity hazard) normally sodium has destroyed the perma - crops, vegetable crops, and fruit have a pH value below 8.5, are rel - nent structure which tends to crops which are generally the atively low in sodium and contain make the soil impervious to most sensitive. principally sodium, calcium and water. Thus, leaching alone will Table 9 lists the chloride toler - magnesium chlorides and sulfates. not be effective unless the high ance of a number of agricultural These compounds cause the white salt method or amend - crops. Boron crust which forms on the surface ments are used. is a major concern in some areas. While a necessary nutrient, high Table 4. Permissible limits for classes of irrigation water. boron levels cause plant toxicity, Concentration, total dissolved solids and concentrations should not exceed those given in Table 10. Classes of water Electrical Gravimetric ppm Some information is available on conductivity µmhos* the susceptibility of crops to Class 1, Excellent 250 175 foliar injury from spray irrigation Class 2, Good 250-750 175-525 with water containing sodium and Class 3, Permissible 1 750-2,000 525-1,400 chloride (Table 11). The tolerance Class 4, Doubtful 2 2,000-3,000 1,400-2,100 of crops to sodium as measured Class 5, Unsuitable 2 3,000 2,100 by the exchangeable sodium per - centage (ESP) is given in Table *Micromhos/cm at 25 degrees C. 12. 1Leaching needed if used 2Good drainage needed and sensitive plants will have difficulty obtaining stands

Table 5. The sodium hazard of water based on SAR Values. SAR values Sodium hazard of water Comments 1-10 Low Use on sodium sensitive crops such as avocados must be cautioned. 10 - 18 Medium Amendments (such as Gypsum) and leaching needed. 18 - 26 High Generally unsuitable for continuous use. > 26 Very High Generally unsuitable for use.

7 Table 7. Soil salinity tolerance levels 1 for different crops. Salinity and (Adapted from Ayers and Westcot, 1976) Growth Stage Yield potential, EC e Many crops have little tolerance Crop 100% 90% 75% 50% Maximum EC e for salinity during seed germina - Field crops tion, but significant tolerance dur - Barley a 8.0 10.0 13.0 18.0 28 ing later growth stages. Some Bean (field) 1.0 1.5 2.3 3.6 7 crops such as barley, wheat and Broad bean 1.6 2.6 4.2 6.8 12 corn are known to be more sensi - Corn 1.7 2.5 3.8 5.9 10 tive to salinity during the early growth period than during germi - Cotton 7.7 9.6 13.0 17.0 27 nation and later growth periods. Cowpea 1.3 2.0 3.1 4.9 9 Sugar beet and safflower are rela - Flax 1.7 2.5 3.8 5.9 10 tively more sensitive during ger - Groundnut 3.2 3.5 4.1 4.9 7 mination, while the tolerance of Rice (paddy) 3.0 3.8 5.1 7.2 12 soybeans may increase or Safflower 5.3 6.2 7.6 9.9 15 decrease during different growth Sesbania 2.3 3.7 5.9 9.4 17 periods depending on the variety. Sorghum 4.0 5.1 7.2 11.0 18 Soybean 5.0 5.5 6.2 7.5 10 Leaching for Salinity Sugar beet 7.0 8.7 11.0 15.0 24 Management Wheat a 6.0 7.4 9.5 13.0 20 Vegetable crops Soluble salts that accumulate in Bean 1.0 1.5 2.3 3.6 7 soils must be leached below the Beet b 4.0 5.1 6.8 9.6 15 crop root zone to maintain pro - Broccoli 2.8 3.9 5.5 8.2 14 ductivity. Leaching is the basic Cabbage 1.8 2.8 4.4 7.0 12 management tool for controlling Cantaloupe 2.2 3.6 5.7 9.1 16 salinity. Water is applied in excess Carrot 1.0 1.7 2.8 4.6 8 of the total amount used by the Cucumber 2.5 3.3 4.4 6.3 10 crop and lost to evaporation. The Lettuce 1.3 2.1 3.2 5.2 9 strategy is to keep the salts in Onion 1.2 1.8 2.8 4.3 8 solution and flush them below the root zone. The amount of water Pepper 1.5 2.2 3.3 5.1 9 needed is referred to as the leach - Potato 1.7 2.5 3.8 5.9 10 ing requirement or the leaching Radish 1.2 2.0 3.1 5.0 9 fraction . Spinach 2.0 3.3 5.3 8.6 15 Excess water may be applied with Sweet corn 1.7 2.5 3.8 5.9 10 every irrigation to provide the Sweet potato 1.5 2.4 3.8 6.0 11 water needed for leaching. How- Tomato 2.5 3.5 5.0 7.6 13 ever, the time interval between Forage crops leachings does not appear to be Alfalfa 2.0 3.4 5.4 8.8 16 critical provided that crop toler - Barley hay a 6.0 7.4 9.5 13.0 20 ances are not exceeded. Hence, Bermudagrass 6.9 8.5 10.8 14.7 23 leaching can be accomplished Clover, Berseem 1.5 3.2 5.9 10.3 19 with each irrigation, every few Corn (forage) 1.8 3.2 5.2 8.6 16 irrigations, once yearly, or even Harding grass 4.6 5.9 7.9 11.1 18 longer depending on the severity Orchard grass 1.5 3.1 5.5 9.6 18 of the salinity problem and salt Perennial rye 5.6 6.9 8.9 12.2 19 tolerance of the crop. An occa - sional or annual leaching event Sudan grass 2.8 5.1 8.6 14.4 26 where water is ponded on the sur - Tall fescue 3.9 5.8 8.61 3.3 23 face is an easy and effective Tall wheat grass 7.5 9.9 13.3 19.4 32 method for controlling soil salini - Trefoil, big 2.3 2.8 3.6 4.9 8 ty. In some areas, normal rainfall Trefoil, small 5.0 6.0 7.5 10.0 15 provides adequate leaching. Wheat grass 7.5 9.0 11.0 15.0 22

8 Table 7. Soil salinity tolerance levels 1 for different crops. Determining Required (continued) Leaching Fraction Yield potential, EC e The leaching fraction is commonly Crop 100% 90% 75% 50% Maximum EC e calculated using the following Fruit crops relationship:

Almond 1.5 2.0 2.8 4.1 7 EC iw Apple, Pear 1.7 2.3 3.3 4.8 8 LF = (1) Apricot 1.6 2.0 2.6 3.7 6 EC e Avocado 1.3 1.8 2.5 3.7 6 where Date palm 4.0 6.8 10.9 17.9 32 LF = leaching fraction Fig, Olive, - the fraction of Pomegranate 2.7 3.8 5.5 8.4 14 applied irrigation Grape 1.5 2.5 4.1 6.7 12 water that must Grapefruit 1.8 2.4 3.4 4.9 8 be leached Lemon 1.7 2.3 3.3 4.8 8 through the root Orange 1.7 2.3 3.2 4.8 8 zone Peach 1.7 2.2 2.9 4.1 7 EC iw = electric conductiv- Plum 1.5 2.1 2.9 4.3 7 ity of the irriga- Strawberry 1.0 1.3 1.8 2.5 4 tion water Walnut 1.7 2.3 3.3 4.8 8 EC = the electric con- 1 e Based on the electrical conductivity of the saturated extract taken from a ductivity of the root zone soil sample (EC e) measured in mmhos/cm. soil in the root a During germination and seedling stage EC e should not exceed 4 to 5 zone mmhos/cm except for certain semi-dwarf varieties. Equation (1) can be used to deter - bDuring germination EC should not exceed 3 mmhos/cm. e mine the leaching fraction neces - sary to maintain the root zone at a 1 targeted salinity level. If the Table 8. Irrigation water salinity tolerances for different crops. amount of water available for (Adapted from Ayers and Westcot, 1976) leaching is fixed, then the equation Yield potential, EC iw can be used to calculate the salini - Crop 100% 90% 75% 50% ty level that will be maintained in the root zone with that amount of Field crops leaching. Please note that equation Barley 5.0 6.7 8.7 12.0 (1) simplifies a complicated soil Bean (field) 0.7 1.0 1.5 2.4 water process. EC e should be Broad bean 1.1 1.8 2.0 4.5 checked periodically and the Corn 1.1 1.7 2.5 3.9 amount of leaching adjusted Cotton 5.1 6.4 8.4 12.0 accordingly. Cowpea 0.9 1.3 2.1 3.2 Based on this equation, Table 13 Flax 1.1 1.7 2.5 3.9 lists the amount of leaching need - Groundnut 2.1 2.4 2.7 3.3 ed for different classes of irriga - Rice (paddy) 2.0 2.6 3.4 4.8 tion waters to maintain the soil Safflower 3.5 4.1 5.0 6.6 salinity in the root zone at a Sesbania 1.5 2.5 3.9 6.3 desired level. However, additional Sorghum 2.7 3.4 4.8 7.2 water must be supplied because of Soybean 3.3 3.7 4.2 5.0 the inefficiencies of irrigation sys - Sugar beet 4.7 5.8 7.5 10.0 tems (Table 14), as well as to Wheat 4.0 4.9 6.4 8.7 remove the existing salts in the soil. Vegetable crops Bean 0.7 1.0 1.5 2.4 Beet 2.7 3.4 4.5 6.4 Broccoli 1.9 2.6 3.7 5.5

9 Table 8. Irrigation water salinity tolerances 1 for different crops. Subsurface Drainage (continued) Yield potential, EC Very saline, shallow water tables iw occur in many areas of Texas. Crop 100% 90% 75% 50% Shallow water tables complicate Cabbage 1.2 1.9 2.9 4.6 salinity management since water Cantaloupe 1.5 2.4 3.8 6.1 may actually move upward into Carrot 0.7 1.1 1.9 3.1 the root zone, carrying with it dis - Cucumber 1.7 2.2 2.9 4.2 solved salts. Water is then extract - Lettuce 0.9 1.4 2.1 3.4 ed by crops and evaporation, leav - Onion 0.8 1.2 1.8 2.9 ing behind the salts. Pepper 1.0 1.5 2.2 3.4 Shallow water tables also con - Potato 1.1 1.7 2.5 3.9 tribute to the salinity problem by Radish 0.8 1.3 2.1 3.4 restricting the downward leaching Spinach 1.3 2.2 3.5 5.7 of salts through the soil profile. Installation of a subsurface Sweet corn 1.1 1.7 2.5 3.9 drainage system is about the only Sweet potato 1.0 1.6 2.5 4.0 solution available for this situa - Tomato 1.7 2.3 3.4 5.0 tion. The original clay tiles have Forage crops been replaced by plastic tubing. Alfalfa 1.3 2.2 3.6 5.9 Modern drainage tubes are cov - Barley hay 4.0 4.9 6.3 8.7 ered by a “sock” made of fabric Bermudagrass 4.6 5.7 7.2 9.8 to prevent clogging of the small Clover, Berseem 1.0 2.1 3.9 6.8 openings in the plastic tubing. Corn (forage) 1.2 2.1 3.5 5.7 A schematic of a subsurface Harding grass 3.1 3.9 5.3 7.4 drainage system is shown in Orchard grass 1.0 2.1 3.7 6.4 Figure 2. The design parameters Perennial rye 3.7 4.6 5.9 8.1 are the distance between drains Sudan grass 1.9 3.4 5.7 9.6 (L) and the elevation of the drains Tall fescue 2.6 3.9 5.7 8.9 (d) above the underlying impervi - Tall wheat grass 5.0 6.6 9.0 13.0 ous or restricting layer. Proper Trefoil, big 1.5 1.9 2.4 3.3 spacing and depth maintain the water level at an optimum level, Trefoil, small 3.3 4.0 5.0 6.7 shown here as the distance m Wheat grass 5.0 6.0 7.4 9.8 above the drain tubes. The USDA Fruit crops Natural Resources Conservation Almond 1.0 1.4 1.9 2.7 Service (NRCS) has developed Apple, Pear 1.0 1.6 2.2 3.2 drainage design guidelines that Apricot 1.1 1.3 1.8 2.5 are used throughout the United Avocado 0.9 1.2 1.7 2.4 States. A drainage computer Date palm 2.7 4.5 7.3 12.0 model developed by Wayne Fig, Olive, Skaggs at North Carolina State Pomegranate 1.8 2.6 3.7 5.6 University, DRAINMOD, is also Grape 1.0 1.7 2.7 4.5 widely used throughout the world Grapefruit 1.2 1.6 2.2 3.3 for subsurface drainage design. Lemon 1.1 1.6 2.2 3.2 Seed Placement Orange 1.1 1.6 2.2 3.2 Peach 1.1 1.4 1.9 2.7 Obtaining a satisfactory stand is Plum 1.0 1.4 1.9 2.8 often a problem when furrow irri - Strawberry 0.7 0.9 1.2 1.7 gating with . Growers Walnut 1.1 1.6 2.2 3.2 1 sometimes compensate for poor Based on the electrical conductivity of the irrigation water (EC iw ) measured germination by planting two or in mmhos/cm. three times as much seed as nor - mally would be required.

10 However, planting procedures can soils. Another practice is to use Residue Management be adjusted to lower the salinity in sloping beds, with the seeds plant - the soil around the germinating ed on the sloping side just above The common saying “salt loves seeds. Good salinity control is the water line (Fig. 3b). Seed and bare soils” refers to the fact that often achieved with a combination plant placement is also important exposed soils have higher evapora - of suitable practices, bed shapes with the use of . tion rates than those covered by and irrigation water management. Typical wetting patterns of drip residues. Residues left on the soil emitters and micro-sprinklers are surface reduce evaporation. Thus, In furrow-irrigated soils, planting less salts will accumulate and rain - seeds in the center of a single-row, shown in Figure 4. Salts tend to move out and upward, and will fall will be more effective in pro - raised bed places the seeds exactly viding for leaching. where salts are expected to con - accumulate in the areas shown. centrate (Figure 3). This situation Other Salinity More Frequent can be avoided using “salt ridges.” Irrigations With a double-row raised planting Management bed, the seeds are placed near the Salt concentrations increase in the shoulders and away from the area Techniques soil as water is extracted by the of greatest salt accumulation. crop. Typically, salt concentrations Alternate-furrow irrigation may Techniques for controlling salinity are lowest following an irrigation help in some cases. If alternate that require relatively minor and higher just before the next irri - furrows are irrigated, salts often changes are more frequent irriga - gation. Increasing irrigation fre - can be moved beyond the single tions, selection of more salt-toler - quency maintains a more constant seed row to the non-irrigated side ant crops, additional leaching, pre - moisture content in the soil. Thus, of the planting bed. Salts will still plant irrigation, bed forming and more of the salts are then kept in accumulate, but accumulation at seed placement. Alternatives that solution which aids the leaching the center of the bed will be require significant changes in process. Surge flow irrigation is reduced. management are changing the irri - often effective at reducing the With either single- or double-row gation method, altering the water minimum depth of irrigation that plantings, increasing the depth of supply, land-leveling, modifying can be applied with furrow irriga - the water in the furrow can the soil profile, and installing sub - tion systems. Thus, a larger num - improve germination in saline surface drainage. ber of irrigations are possible using the same amount of water.

Figure 2. A subsurface drainage system. Plastic draintubes are located a distance (L) apart.

11 Figure 3a. Single-row versus double-row beds showing areas of salt accumulation following a heavy irrigation with salty water. Best planting position is on the shoulders of the double-row bed.

Figure 3b. Pattern of salt build-up as a function of seed placement, bed shape and irrigation water quality.

12 Table 9. Chloride tolerance of agricultural crops. Listed in order With proper placement, drip irriga - of tolerance a. (Adapted from Tanji. 1990) tion is very effective at flushing - b salts, and water can be applied Maximum Cl concentration almost continuously. Center pivots without loss in yield 3 equipped with LEPA water appli - Crop mol/m ppm cators offer similar efficiencies and Strawberry 10 350 control as drip irrigation at less Bean 10 350 than half the cost. Both sprinkler Onion 10 350 and drip provide more control and flexibility in scheduling irrigation Carrot 10 350 than furrow systems. Radish 10 350 Lettuce 10 350 Preplant Irrigation Turnip 10 350 c d Salts often accumulate near the Rice, paddy 30 1,050 soil surface during fallow periods, Pepper 15 525 particularly when water tables are Clover, strawberry 15 525 high or when off-season rainfall is Clover, red 15 525 below normal. Under these condi - Clover, alsike 15 525 tions, seed germination and seedling growth can be seriously Clover, ladino 15 525 reduced unless the soil is leached Corn 15 525 before planting. Flax 15 525 Potato 15 525 Changing Surface Sweet potato 15 525 Irrigation Method Broad bean 15 525 Surface irrigation methods, such as Cabbage 15 525 flood, basin, furrow and border are Foxtail, meadow 15 525 usually not sufficiently flexible to Celery 15 525 permit changes in frequency of Clover, Berseem 15 525 irrigation or depth of water applied Orchardgrass 15 525 per irrigation. For example, with furrow irrigation it may not be Sugarcane 15 525 possible to reduce the depth of Trefoil, big 20 700 water applied below 3-4 inches. Lovegras 20 700 As a result, irrigating more fre - Spinach 20 700 quently might improve water avail - Alfalfa 20 700 ability to the crop but might also c Sesbania 20 700 waste water. Converting to surge flow irrigation may be the solution Cucumber 25 875 for many furrow systems. Tomato 25 875 Otherwise a sprinkler or drip irri - Broccoli 25 875 gation system may be required. Squash, scallop 30 1,050 Vetch, common 30 1,050 Chemical Amendments Wild rye, beardless 30 1,050 In sodic soils (or sodium affected Sudan grass 30 1,050 soils), sodium ions have become Wheat grass, standard crested 35 1,225 attached to and adsorbed onto the c Beet, red 40 1,400 soil particles. This causes a break - down in soil structure and results Fescue, tall 40 1,400 in or “cementing,” Squash, zucchini 45 1,575 making it difficult for water to Harding grass 45 1,575 infiltrate. Chemical amendments Cowpea 50 1,750 are used in order to help facilitate Trefoil, narrow-leaf bird’s foot 50 1,750 the displacement of these sodium ions. Amendments are composed

13 Table 9. Chloride tolerance of agricultural crops. Listed in order References of tolerance a. (continued) - b Maximum Cl concentration Ayres, R.S. and D.W. Westcot. without loss in yield 1976. Water Quality for 3 Crop mol/m ppm . Irrigation and Drainage Paper No. 29. Food Ryegrass, perennial 55 1,925 and Agriculture Organization Wheat, Durum 55 1,925 of the United Nations. Rome. c Barley (forage) 60 2,100 c Cuena, R.H. 1989. Irrigation Wheat 60 2,100 System Design . Prentice Hall, Sorghum 70 2,450 Englewood Cliffs, NJ. 552pp. Bermudagrass 70 2,450 Hoffman, G.S., R.S. Ayers, E.J. c Sugar beet 70 2,450 Doering and B.L. McNeal. Wheat grass, fairway crested 75 2,625 1980. Salinity in Irrigated Cotton 75 1,625 Agriculture. In: Design and Operation of Farm Irrigation Wheat grass, tall 75 2,625 c Systems . M.E. Jensen, Editor. Barley 80 2,800 ASAE Monograph No. 3. St. aThese data serve only as a guideline to relative tolerances among crops. Joseph, MI. 829pp. Absolute tolerances vary, depending upon climate, soil conditions and cultural practices. James, D.W., R.J. Hanks and J.H. – bCl concentrations in saturated-soil extracts sampled in the rootzone. Jurinak. 1982. Modern c Irrigated Soils . John Wiley Less tolerant during emergence and seedling stage. and Sons, NY. d – Values for paddy rice refer to the Cl concentration in the during Jensen, M.E. (Editor). 1980. the flooded growing conditions. Design and Operation of Farm Irrigation Systems . American Society of of sulphur in its elemental form or References section present equa - Agricultural Engineers, St. related compounds such as sulfu - tions that are used to determine Joseph MI. 829pp. ric acid and gypsum. Gypsum also the amount of amendments needed Longenecker, D.E. and P.J. contains calcium which is an based on soil analysis results. Lyerly. 1974. B-876 Control important element in correcting of Soluble Salts in Farming these conditions. Some chemical Pipe Water Delivery and Gardening. Texas amendments render the natural Systems Stabilize Agricultural Experiment calcium in the soil more soluble. Salinity Station, Texas A&M As a result, calcium replaces the University System, College adsorbed sodium which helps As illustrated in Fig. 1, any open Station. June. 36pp. restore the capacity of water is subject to evaporation Pair, C.H. (editor). 1983. the soil. Polymers are also begin - which leads to higher salt concen - Irrigation . The Irrigation ning to be used for treating sodic trations in the water. Evaporation Assoc., Arlington, VA. 680pp. soils. rates from water surfaces often Rowe, D.R. and I.M. Abdel- It is important to note that use of exceed 0.25 inch a day during Magid. 1995. Handbook of amendments does not eliminate summer in Texas. Thus, the salini - Wastewater Reclamation and the need for leaching. Excess ty content of irrigation water will Reuse . CRC Press, Inc. water must still be applied to leach increase during the entire time 550pp. out the displaced sodium. water is transported through irriga - Chemical amendments are only tion canals or stored in reservoirs. Stewart, B.A. and D.R. Nielsen. effective on sodium-affected soils. Replacing irrigation ditches with 1990. Irrigation of Amend-ments are ineffective for pipe systems will help stabilize Agricultural Crops . American saline soil conditions and often salinity levels. In addition, pipe Society of Agronomy. will increase the existing salinity systems, including gated pipe and 1,218pp. problem. Table 15 lists the most lay-flat tubing, reduce water lost Tanji, K.K. 1990. Agricultural common amendments. The irriga - to canal seepage and increase the Salinity Assessment and tion books listed under the amount of water available for Management . American leaching. Society of Civil Engineers. 14 Manuals and Reports on van der Leeden, F., F.L. Troise and Engineering Practice Number D.K. Todd. 1990. The Water 71. 619pp. Encyclopedia . Lewis Publishers. 808pp.

Figure 4. Typical wetting patterns and areas of salt accumulation with drip emitters and micro-sprinklers sprayers.

15 Table 10. Limits of boron in irrigation water. (Adapted from Rowe and Abdel-Magid, 1995) A. Permissible Limits (Boron in parts per million) Class of water Crop group Sensitive Semitolerant Tolerant Excellent <0.33 <0.67 <1.00 Good 0.33 to 0.67 0.67 to 1.33 1.00 to 2.00 Permissible 0.67 to 1.00 1.33 to 2.00 2.00 to 3.00 Doubtful 1.00 to 1.25 2.00 to 2.50 3.00 to 3.75 Unsuitable >1.25 >2.5 >3.75 B. Crop groups of boron tolerance (in each plant group, the first names are considered as being more tolerant; the last names, more sensitive). Sensitive Semitolerant Tolerant (1.0 mg/L of Boron) (2.0 mg/L of Boron) (4.0 mg/L of Boron) Pecan Sunflower (native) Athel (Tamarix aphylla) Walnut (Black, Persian, or English) Potato Asparagus Jerusalem artichoke Cotton (Acala and Pima) Palm ( canariensis) Navy bean Tomato Date palm (P. dactylifera) American elm Sweetpea Sugar beet Plum Radish Mangel Pear Field pea Garden beet Apple Ragged Robin rose Alfalfa Grape (Sultania and Malaga) Olive Gladiolus Kadota fig Barley Broad bean Persimmon Wheat Onion Cherry Corn Turnip Peach Milo Cabbage Apricot Oat Lettuce Thornless blackberry Zinnia Carrot Orange Pumpkin Avocado Bell pepper Grapefruit Sweet potato Lemon Lima bean (0.3 mg/L of Boron) (1.0 mg/L of Boron) (2.0 mg/L of Boron)

Table 11. Relative susceptibility of crops to foliar injury from saline sprinkling waters. (Tanji, 1990) Na or Cl concentration (mol/m3) causing foliar injury a <5 5-10 10-20 >20 Almond Grape Alfalfa Cauliflower Apricot Pepper Barley Cotton Citrus Potato Corn Sugar beet Plum Tomato Cucumber Sunflower Safflower Sesame Sorghum aFoliar injury is influenced by cultural and environmental conditions. These data are presented only as general guidelines for daytime sprinkling.

16 Table 12. Tolerance of Various Crops to Exchangeable-Sodium Percentage. (James et al., 1982) Tolerance to ESP Growth Responsible (range at which affected) Crop Under Field Conditons Extremely sensitive Deciduous fruits Sodium toxicity symptoms even at (ESP = 2-10) Nuts low ESP values Citrus Avocado Sensitive Beans Stunted growth at low ESP values (ESP = 10-20) even though the physical condition of the soil may be good Moderately tolerant Clover Stunted growth due to both (ESP = 20-40) Oats nutritional factors and adverse soil Tall fescue conditions Rice Dallisgrass Tolerant Wheat Stunted growth usually due to (ESP = 40-60) Cotton adverse physical conditions of soil Alfalfa Barley Tomatoes Beets Most tolerant Crested and Fairway wheatgrass Stunted growth usually due to (ESP > 60) Tall wheatgrass adverse physical conditions of soil Rhodes grass

Table 13. Leaching requirement* as related to the electrical conductivities of the irrigation and drainage water. Electrical conductivity of Leaching requirement based on the indicated maximum values for the irrigation water (mmhos/cm) conductivity of the drainage water at the bottom of the root zone 4 mmhos/cm 8 mmhos/cm 12 mmhos/cm 16 mmhos/cm Percent Percent Percent Percent 0.75 13.3 9.4 6.3 4.7 1.00 25.0 12.5 8.3 6.3 1.25 31.3 15.6 10.4 7.8 1.50 37.5 18.7 12.5 9.4 2.00 50.0 25.0 16.7 12.5 2.50 62.5 31.3 20.8 15.6 3.00 75.0 37.5 25.0 18.7 5.00 — 62.5 41.7 31.2 *Fraction of the applied irrigation water that must be leached through the root zone expressed as percent.

17 Table 14. Typical overall on-farm efficiencies for various types of irrigation systems. System Overall efficiency (%) Surface 50-80 a. average 50 b. land leveling and delivery pipeline meeting design standards 70 c. tailwater recovery with (b) 80 d. surge 60-90* Sprinkler (moving and fixed systems) 55-85 LEPA (low precision application) 95-98 Drip 80-90** *Surge has been found to increase efficiencies 8 to 28% over non-surge furrow systems. **Drip systems are typically designed at 90% efficiency, short laterals (100 feet) or systems with pressure compen- sating emitters may have higher efficiencies.

Table 15. Various amendments for reclaiming sodic soil and amount equivalent to gypsum. Amendment Physical description Amount equivalent 100% gypsum Gypsum* White mineral 1.0 Sulfur† Yellow element 0.2 * Corrosive liquid 0.6 Lime sulfur* Yellow-brown solution 0.8 † White mineral 0.6 Calcium chloride* White salt 0.9 Ferrous sulfate* Blue-green salt 1.6 Pyrite† Yellow-black mineral 0.5 Ferric sulfate* Yellow-brown salt 0.6 Aluminum sulfate* Corrosive granules 1.3 *Suitable for use as a water or soil amendment. †Suitable only for soil application.

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