Hill, Robert

Koenig, Richard T.

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1WATER SALINITY AND CROP YIELD    Robert Hill and Richard T. KoenigMay 1999                                      Utah Water Quality                                      AG-425.3WATER SALINITYIrrigated agriculture in Utah depends on adequate, high-quality water supplies. As thelevel of salt increases in an irrigation source, the quality of that water for plant growth decreases.All irrigation waters contain some salt. In many areas, good quality (low salt and low sodium)water is not available for irrigation, consequently waters containing high levels of salt must beused.A measure of water salinity that is important for crop yield is Electrical Conductivity(EC). EC is measured in units of deci-siemens per meter, or dS/m. The higher the EC the higherthe level of salts in the water and the more difficult it is to grow plants with that water. Increasingsalinity affects growth mainly by reducing the plants ability to absorb water.CROP YIELD RESPONSE TO SALINITYConsiderable study relating crop yield response to waters of different salinities has beensummarized in “Water Quality for Agriculture” (1). Generally, crops are classified into fourmajor groups: sensitive, moderately sensitive, moderately tolerant, or tolerant of salinity inirrigation waters (Table 1).Table 1. Relative salinity tolerance categories for typical Utah crops (listed in order ofdecreasing tolerance). Salinity tolerance information for additional crops can beobtained from reference 3 at the end of this guide.Tolerant Barley, Sugar Beet, Wildrye, AsparagusModerately Tolerant Wheat, Wheat Grass, Zucchini, Beet (red)Moderately Sensitive Tomato, Cucumber, Alfalfa, Clover, Corn, Muskmellon, Potato Sensitive Onion, Carrot, Bean, Apple, Cherry, Raspberry, Strawberry2Possible yield response of various crops to different levels of salinity is shown in Figure1. The relationship between ECe (the EC of the soil saturation extract) and ECw (the EC of theirrigation water) is indicated on the graph. When sufficient irrigation water is applied to cause15% of the water to percolate through the root zone, then the ECe is approximately equal to 1.5ECw. This deep percolation of water through the root zone is necessary to continue leaching ofaccumulated salts out of the active root areas. For example, if the ECw is 5 dS/m, then the ECewould be approximately 7.5 dS/m and the expected yield of alfalfa would be only 60% of what itcould be with better quality water. This still assumes that 15% of the applied water moves downthrough the root zone as deep percolation to leach salts out. If the irrigation system design oroperation is such that the application rate just meets the plant requirements and there was noleaching, the expected yield would be less than that shown on the graph.Figure 1. Divisions for relative salt tolerance ratings of agricultural crops (adapted fromFig 10, FAO #29). The graph assumes 15% of infiltrated water is leaching. Yield willbe reduced more than the graph shows if leaching is insufficient. Relative yieldresponses of alfalfa, wheat and barley to salinity are shown by dashed lines.3Leaching Fraction (LF)  Depth of Water Leached Below theRoot ZoneDepth of Water Applied at the SurfaceTYPICAL UTAH IRRIGATION WATER SALINITIESWater quality samples have been collected at different times and in different locations throughoutUtah. James and Jurinak (2) summarized the ECw for various drainage and river systems. Anextract of their data is given in Table 2. Also included in Table 2 are the expected yields ofalfalfa, barley and wheat if irrigated with waters of this quality (as determined from Figure 1). There is considerable variability in water salinities around Utah. Most of the streams inCache Valley are high quality, having ECw values of 0.3 to 0.5 dS/m. The Bear River,particularly the downstream reaches, has higher salinity levels. Generally, as rivers first emergefrom mountains along the Wasatch Front, Uintah Basin, and other areas, they have salinities lessthan 2 dS/m.In southern Utah, the Virgin River at La Verkin has EC values which vary from 2.7 to 9.1dS/m depending on the time of year in which the sample was taken. LaVerkin Creek, nearLaVerkin, has the highest ECw of any surface stream included in the data. With an ECw of 11.4dS/m, alfalfa would not grow. Wheat yield would be reduced to about 20% and barley to 55% oftheir potential yields for well managed conditions in that area.Also included in Table 2 are well samples from Western Box Elder County. The well atHowell, which is used for center pivot irrigation, has an EC of 4.5 dS/m. This level would reducealfalfa to 66% and wheat to 95% of possible yields, but would not affect barley yield.As a general rule, surface water supplies affected by irrigation return flows will havehigher conductivity levels later in the summer and early fall. Lower ECw values will beexperienced during the spring because of dilution from snow melt.IRRIGATION WATER ANALYSISIrrigation water analysis should include EC, calcium, magnesium, sodium, chloride,carbonate, bicarbonate, sulfate, and boron. The Utah State University Analytical Lab offers anirrigation water quality analysis package including the above parameters for a cost of $15.00 persample. Contact your County Extension Agent for more information on how to collect a watersample and where to send the sample for analysis.ESTIMATING LEACHING REQUIREMENTSFigure 1 is based on standard guidelines that assume the ECe is 1.5 times the ECw andthat the leaching fraction is about 0.15 (15%). In actuality, the relationship between ECe andECw depends on the amount of water added for leaching purposes. The leaching fraction (or requirement) is the amount of water, in excess of consumptiveuse, necessary to wash the accumulated soil salts below the root zone:[1]4Table 2. Water quality samples taken in various Utah locations and its estimated effect onrelative crop yield.Location Date Electrical %EstimatedConductivitya Relative YieldbdS/m Alfalfa Barley WheatSurface StreamsGreat Salt Lake drainage,B.R. Sage Creek Junction 9-81   .79 100 100 100B.R. Culter Dam 9-81   .91 100 100 100B.R. Corinne 9-81 4.01   71 100 100Logan River, Logan 9-81  .40 100 100 100Little Bear River, Hyrum Reservoir 8-81  .47 100 100 100Malad River, Bear River City 8-81 2.01   93 100 100Ogden River 9-81  .67 100 100 100Weber River 9-81  .55 100 100 100Strawberry Reservoir 9-81  .59 100 100 100Spanish Fork River, Spanish Fork 9-81  .40 100 100 100Provo River, Provo 9-81  .40 100 100 100Jordan River, Riverton 9-81 1.74  96 100 100Sevier River, below Panguitch 9-81  .40 100 100 100Sevier River, Gunnison 9-81 2.30   90 100 100Delta Reservoir 9-81 2.14   91 100 100Chalk Creek, Fillmore 9-81  .40 100 100 100Beaver River, Beaver 9-81  .29 100 100 100Parowan Creek 9-81  .41 100 100 100La Verkin Creek 9-81 11.40    0   55   21Virgin River, LaVerkin 7-81 9.13  16   75   45Virgin River, LaVerkin 9-81 2.73  85 100 100Uintah River Whitrocks 9-81   .06 100 100 100Uintah River, Randlett 9-81 2.12   92 100 100Duchesne River, North Fork Tabiona 9-81   .47 100 100 100Strawberry River, Duchesne 9-81   .74 100 100 100Duchesne River, Ouray 9-81 1.07 100 100 100Ashley Creek, Vernal 9-81 2.79   84 100 100Snowville Creek 9-88 1.84   95 100 100Fremont River, Bicknell 9-81   .48 100 100 100Wells in Western Box Elder CountyRose Ranch Pivot 9 9-88  3.6    76 100 100Rose Ranch Pivot 17 6-88  5.6    52   97   80Howell (Mike Weston) 9-88  4.5    66 100   95Alder Ranch 9-88  3.1    81 100 100aConductivity of irrigation water (ECw) expressed as dS/m.bEstimated possible yields are shown as a percentage of potential.  These estimated yields assume that 15% ofinfiltrated water is leaching.  Yield reduction is (100 - relative yield); example: if the relative yield is 52% then theyield reduction is 48% (48 = 100 - 52).5LF ECw5ECetl  ECwDawET(1  LF)LF  3.15×2.0  3.1 0.45Daw33(1  0.45)  60 inchesAn estimate of the leaching fraction to maintain a desired crop yield can be made if theirrigation water salinity (ECw) and the soil salinity at the desired crop tolerance level (ECetl) areknown (adapted from eq. 9 of FAO 29):[2]where LF is the minimum leaching fraction necessary for maintaining salts within the croptolerance soil salinities with above ground irrigation methods, ECw is the salinity of the appliedirrigation water (dS/m), and ECetl is the average saturated soil extract salinity (dS/m) toleratedby the crop.The total annual applied water depth (assuming no precipitation) required to satisfy bothET and leaching is:[3]Daw is the depth of applied water and ET is the consumptive use (both in inches/year). Crop wateruse (ET) values for locations around Utah are available in Hill (1994). Depending on the timingand the amount, excess natural precipitation that contributes to deep percolation can significantlyreduce the leaching requirement from irrigation. Since the crop senses soil salinity as opposed toirrigation water salinity, if extra leaching water is received in the form of natural precipitation,higher salinity irrigation water can be utilized with limited crop losses.Example. Assume that well water with an EC of 3.1 dS/m was available to irrigate alfalfa. Whatis the required leaching fraction to maintain yields at 100%? From Figure 1 (or references 1 or 3)the ECetl is 2.0 ds/m or less in order for alfalfa yields to be 100% (no yield loss due to soilsalinity). The corresponding leaching fraction from Equation 2 is:Expressed as a percent, this means that 45% of the irrigation water must pass through the rootzone to provide sufficient salt removal.If this were an area where the annual crop water use (ET) of alfalfa was 33 inches, thenthe total annual applied irrigation water depth should be (from Equation 3):This is equivalent to 5 acre-feet per acre of infiltrated irrigation water and does not includedistribution, conveyance, tailwater surface runoff, or other losses. Additional discussion andmore technical details are contained in reference 1, and beginning on page 131 in reference 4,listed at the end of this guide.6Utah State University Extension is an affirmative action/equal employment opportunity employer andeducational organization. We offer our programs to persons regardless of race, color, national origin, sex,religion, age or disability.Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperationwith the U.S. Department of Agriculture, Robert L. Gilliland, Vice-President and Director, CooperativeExtension Service, Utah State University, Logan, Utah. (EP/05-99/DF) REFERENCES1.  Ayers, R. S., and D. W. Westcot. 1985. Water Quality for Agriculture. FAO Irrigation andDrainage Paper 29, Rev. 1, U.N. Rome.2. James, D.W., and J. J. Jurinak. 1986. Irrigation Resources in Utah: Water Quality versus SoilSalinity, Soil Fertility and the Environment. Res. Bulletin 514. Utah Ag. Exp. Sta., UtahState University, Logan, UT, 84322. December.3. Kotuby-Amacher, J., R. Koenig, and B. Kitchen. 1997. Salinity and Plant Tolerance.Electronic Publication AG-SO-03, Utah State University Extension, Logan, UT, 84322.July.4. Hill, R.W. 1994. Consumptive Use of Irrigated Crops in Utah. Utah. Agr. Exp. Sta. Res. Rpt.#145. Utah State University, Logan, UT. This report is available on the Web at:http://nrwrtl.nr.state.ut.us/manuals/consumpt/cfwea.htmRobert W. Hill, Professor and Extension Irrigation Specialist,Biological and Irrigation Engineering Department,Utah State University, Logan, UT, 84322-4105.Rich Koenig, Assistant Professor and Extension Soils Specialist,Plants, Soils, and Biometeorology Department, Utah State University, Logan, UT 84322-4820.

Water Salinity and Crop Yield

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Water Salinity and Crop Yield

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