"New/March 1991/10M.""Water Quality.""Published by University Extension. University of Missouri-Columbia.""Focus area : nutrients and bacterial wastes.

Hefner, S. G.

Tracy, P. W.

University of Missouri: MOspace

Focus Area NutrientsWater Bacterial WastesQuality	 and PUBLISHED BY UNIVERSITY EXTENSION. UNIVERSITY OF MISSOURI-COLUMBIA Calculating Crop Nutrient Value from Irrigation Water Inputs: A Survey of Southeast Missouri Irrigation P.W. Tracy and 5.G. Hefner, Extension Agronomy units. To convert irrigation wat~r constituents ApprOximately 600,000 acres of cropland are irrigated annually in Southeast Missouri. Agronomic benefits from timely irrigation practices are well known by agricultural produc­ers in the region. A large shallow water supply ensures inexpensive irrigation, making it a cost effective management practice. Public concern runs high over water quantity and quality. hrigation water sometimes contains elements and compounds such as nitrate or sodium, undesired in terms of human consump­tion, plant growth or soil environmental pro­cesses. However, irrigation water also contains elements or compounds such as nitrate, phos­phate, potassium, sulfate, calcium, magnesium, iron, zinc, copper and manganese, which are essential for plant growth. Proper crop nutrient management often includes fertilization of some of these nutrients. Most producers do not con­sider irrigation water nutrient concentrations when developing a fertilization program. This overlooked source of plant nutrients is impor­tant, and can save producers money and prevent adding of non-essential quantities of nutrients to the agri-ecosystem. The purpose of this report is to educate irrigators to the potential nutrient value of their irrigation water. Also included is a summary of an irriga­tion well survey conducted in 1987. Butler, Mississippi, New Madrid, Pemiscot, Ripley, Scott and Stoddard counties in Southeast Missouri, which contain large irrigated acreages, are included in the survey. Calculations When analyzed, most elements present in water samples are reported in parts per million (ppm) from ppm to pounds applied per acre requires the following calculation: 1 acre-foot of water =326,000 gallons water 1 gallon water =8.31 lbs. water , therefore, 1 acre-foot of water weighs 2.7 million lbs. ppm nutrient x 2.7 =lbs. nutrient added per acre­foot. Example calculation: •	 water sample contains 5.3 ppm sulfate (504) •	 a rice crop requires 3.5 acre-feet of water •	 5.3 ppm x 3.5 acre-feet x 2.7Ibs. =54lbs. 504 •	 504 contains 1/3 5 and 2/3 oxygen (0) •	 54/3 =18 lbs. 5 added per year through irrigation water •	 a rice crop requires approximately 15 lbs. 5 per year NOTE: the irrigation water supplied 100% of the rice 5 needs. From this calculation it is obvious that irrigation water typically provides essential crop nutrients. hrigators are advised t<? test wells periodically to take advantage of this "free" fertilizer. With water testing programs being developed throughout the United States, it should not be difficult to have wells tested. Use a reputable private or public laboratory tha~ specializes ~ water testing. If only crop nutrIents (not pestI­cides) are analyzed, then the cost of water testing should be minimal. Unless point source con­tamination has occurred, groundwater generally will contain similar amounts of essential plant nutrients over a small geographic area the size of most farming operations. Therefore, if sampling occurs away from potential point sources (feed­$0.75	 WQ278 Printed with Soy Ink on Recycled Paper. Arhive version -- See extenio.missoui.edulots, fertilizer storage areas, etc.), then a repre­sentative water sample can be obtained from one or two well locations. . 1987 Southeast Missouri Irrigation Well Survey In 1987,~ an irrigatiol\well water survey was conducted by University of Missouri Extension personnel to identify the nutrient content of irrigation waters in Southeast Missouri. The survey was co-funded by the Missouri Rice Council and the Missouri Soybean Merchandis­ing Council. Therefore, regions sampled were those where rice/soybean rotations are preva­lent. A total of 272 wells were sampled in the seven counties. Data collected from each water sample were: well depth, water temperature, water pH, and nitrate, sulfate, phosphate, potas­sium, calcium, magnesium, sodium, iron, zinc, copper, manganese and salt content. Due to high cost, water biological and pesticide composition I was not analyzed. Average county and survey nutrient concentrations are listed in Table 1. General trends showed that irrigation water phosphate (P04), potassium (K), zinc (Zn) and copper (Cu) did not vary across the survey area and were below levels necessary for crop growth. Calculations for total phosphorus and potassium supplied by one acre-foot of irrigation water using regional average concentrations are as follows: 0.4 ppm P04 x 2.7 1.11bs P04, P04 is 33% Pi therefore, 1 acre-foot of irrigation ~ater would supply less than lIb. P. 1.4 ppm K x 2.7 == 3.81bs K applied per acre-foot of irrigation water. A 150 bushel per acre com crop requires ap­proximately 45 pounds phosphorus and 200 pounds potassium. Given the above calcula­tions, it is estimated that irrigation waters in Southeast Missouri potentially can contribute less than 2 percent of the nutritional phosphorus and potassium needs for com. Water manganese concentrations were also uniform across the region, but were high enough to partially pro­vide crops with this essential micro-nutrient. Water pH, electrical conductivity (E.C.), nitrate­nitrogen (N03-N), sulfate (S04)' calcium (Ca), Table 1. Average values of irrigation water composition by county and the entire survey region. OJ ...... ..c co.S:: co > M OJ ~ ~ ..... Q... Q........ tf) .~ tf) tf) ~ "'C.C: "'C co ~ ~ Z ~ 0 u tf)..... S OJ ~ ~ OJ ...... Q... ~ ~ 0 u CJ'J "'C ~ "'C "'C .s CJ'J s:i 0·60 OJ ~ County Average Temp. po 58 57 62 67 59 60 Depth ft. 113 100 93 56 70 102 103 pH 7.6 7.2 7.2 7.2 7.4 7.8 7.3 7.4 * E.C.mmhos 0.5 0.3 0.3 0.5 0.4 0.2 0.5 0.4 * N03-Nppm 0.9 3.3 2.1 0.6 0.8 1.3 1.9 1.6 * SO II 4 3.1 4.5 7.1 11 5.3 10 7.2 6.0 * P0 4 II 0.6 0.4 0.9 0.6 0.0 0.5 0.0 0.4 K" 1.8 3.6 3.7 1.9 1.6 1.3 2.0 1.4 Ca II 249 52 62 81 269 225 115 161 * Mg II 9 16 13 21 6 1 19 12 * Na II 12 8 11 9 10 7 19 13 * Fe II 4.5 1.6 0.5 1.1 1.8 1.2 2.2 2.5 * Zn II 0.0 0.0 0.0 0.1 0.0 0.1 0.0 0.0 Cu II 0.0 0.0 0.0 0.0 0.0 0.8· 0.0 0.1 MN II 0.8 0.4 0.4 0.4 0.6 0.6 0.5 0.6 * D~n~tes.el~ments which had variation across the survey region and have agronomic importance. This vanation IS illustrated by contour maps (Figures 1-8). WQ278 ~ <1.0 ~ 2.5 - 3.99 ~ 7.0 - 7.39 •~ 7.4 - 7.69 § 1.0 - 2.49 • 4.0 - 6.0 7.7 - 8.00 Figure 1: Irrigation water pH concentration Figure 2: Irrigation water nitrate-nitrogen gradients in Souteast Missouri concentration gradients (ppm) in Southeast Missouri magnesium (Mg), sodium (Na) and iron (Fe) concentrations were variable across the region with most present at levels high enough to influence crop production. Contour maps (Figures 1-8) were developed for these compo­nents. County average irrigation water nutrient composition and regional contour maps were developed to identify general trends and may not be representative of site-specific wells lo­cated within counties or map unit delineation areas. Due to low buffer capacity of most irrigation waters, water pH usually will not influence soil or plant systems. However, pH values in most of Scott County and near the St. Francis River in Stoddard and Butler counties approached alka­line levels (Figure 1). Producers should know the pH of their irrigation water, especially if agrichemicals, some of which can be adversely affected by water pH, are mixed with these waters. Producers should check herbicide labels for optimum mixing water pH ranges. Water nitrate concentration has received much attention environmentally over the past several years. However, nitrate contained in irrigation water will provide crops with part of their nitrogen needs. If care is taken to prevent excessive runoff, most nitrate delivered through irrigation water is available to crops. Southeast Missouri irrigation waters varied in nitrate content (Figure 2), but in all cases contained nitrate-nitrogen at levels accepted by the EPA for drinking quality standards «10 ppm). Areas of highest nitrate concentration were central Stoddard County and the tri-county region southeast of Sikeston. Using the Mississippi County average irrigation water nitrate concen­tration (highest nitrate testing county), it is calculated that: 3.3 ppm N03-N x 2.7 =8.9 pounds N is added per acre-foot of irrigation water. A 150 bushel per acre com crop requires ap­proximately 240 pounds of nitrogen per acre. Therefore, irrigation waters in Southeast Mis­souri supply less than 5 percent of a com crop's nitrogen nutritional needs. Sulfur is an essential plant nutrient required in quantities approximately one-tenth of those needed for nitrogen. Most crops require be­tween 10 and 20 pounds of sulfur per acre. As irrigation water approaches 5.0 ppm sulfate (see example calculation), crops receiving irrigation Win benefit in terms of sulfur nutrition. Most irrigation water in Southeast Missouri contains WQ278 1::::::::1 < 1.0 0-" ~ 1.0 -7.5 100 - 1" • 7.5 - 15.0 200 - 400 Figure 3: Irrigation water sulfate concentra­ Figure 4: Irrigation water calcium concentra­tion gradients (ppm) in Southeast Missouri tion gradients (ppm) in Southeast Missouri sulfate concentrations approaching or exceeding 7.5 ppm (Figure 3). Generally, irrigated crops grown in Southeast Missouri may not require sulfur fertilizer inputs. Calcium is a nutrient required by all crops, but rarely is calcium fertilization needed. Calcium usually is added to soils in large quantities via agricultural limestone, or contained at soil clay adsorption sites or in clay mineral composition. Calcium additions. through irrigation water sources in Southeast Miss'ouri are appreciable and commonly approach 400 ppm (Figure 4). Some of this calcium may be fixed by soils or lost ,	 through leaching, but a large amount should be readily available to crops. High amounts of calcium in irrigation water combined with appreciable amounts of carbonate (C03) (not tested in the current survey) will give the water some agricultural limestone value. An example calcium carbonate equivalent (CCE) calculation for irrigation water using the Butler County average calcium concentration, and assuming all calcium is associated with carbonate (maximum possible CCE) is given below: 249 ppm Ca x 2.7 =672 lbs. Ca applied per acre Calcium Carbonate is 40%' Ca and 60% carbonate Therefore, 672/0.40 =1680 lbs. or 0.84 tons potential CCE applied through 1 acre-(oot of irrigation water. Given the high amounts of calcium, especially in a diagonal running northeast from Ripley through southern Scott Counties, it is reasonable to expect that irrigation water is supplying appreciable agricultural limestone value to irrigated fields in Southeast Missouri. Irrigators should soil test routinely to identify agricultural limestone needs. Magnesium deficiencies are rare in the Mid-west. However, magnesium is an essential plant nutrient that is present in Southeast Missouri irrigation water (Figure 5). As discussed with calcium, magnesium in combination with car­bonate will represent some agricultural lime­stone equivalent. In general, magnesium con­centrations in irrigation samples were o~e-tenth those of calcium. Still, if small areas in fields are magnesium-deficient, then irrigation will supply some magnesium crop needs. Iron and manganese were the only essential plant micro-nutrients present in ,sufficient quan­tities to benefit crops (Figure 6 and Table 1). ~ However, deficiencies of these micro-nutrients are rarely reported in Southeast Missouri. Also, these nutrients commonly form precipitate minerals in water or soils. It is not expected that crop iron or manganese nutrition will be affected by levels in irrigation waters. Sodium is not an essential plant nutrient and , WQ278 ~ <1.0 ~ 2.5 - 3.99 ~ 7.0 - 7.39 •~ 7.4 - 7.69 § 1.0 - 2.49 g 4.0 - 6.0 7.7 - 8.00 Figure 1: Irrigation water pH concentration Figure 2: Irrigation water nitrate-nitrogen gradients in Souteast Missouri concentration gradients (ppm) in Southeast Missouri magnesium (Mg), sodium (Na) and iron (Fe) concentrations were variable across the region with most present at levels high enough to influence crop production. Contour maps (Figures 1-8) were developed for these compo­nents. County average irrigation water nutrient composition and regional contour maps were developed to identify general trends and may not be representative of site-specific wells lo­cated within counties or map unit delineation areas. Due to low buffer capacity of most irrigation waters, water pH usually will not influence soil or plant systems. However, pH values in most of Scott County and near the St. Francis River in Stoddard and Butler counties approached alka­line levels (Figure 1). Producers should know the pH of their irrigation water, especially if agrichemicals, some of which can be adversely affected by water pH, are mixed with these waters. Producers should check herbicide labels for optimum mixing water pH ranges. Water nitrate concentration has received much attentioJ;l environmentally over the past several years. However, nitr~te contained in irrigation water will provide crops with part of their nitrogen needs. If care is taken to prevent excessive runoff, most nitrate delivered through irrigation water is available to crops. Southeast Missouri irrigation waters varied in nitrate content (Figure 2), but in all cases contained nitrate-nitrogen at levels accepted by the EPA for drinking quality standards «10 ppm). Areas of highest nitrate concentration were central Stoddard County and the tri-county region southeast of Sikeston. Using the Mississippi County average irrigation water nitrate concen­tration (highest nitrate testing county), it is calculated that: 3.3 ppm N03-N x 2.7 8.9 pounds N is added per acre-foot of irrigation water. A 150 bushel per acre com crop requires ap­proximately 240 pounds of nitrogen per acre. Therefore, irrigation waters in Southeast Mis­souri supply less than 5 percent of a com crop's nitrogen nutritional needs. Sulfur is an essential plant nutrient required in quantities approximately one-tenth of those needed for nitrogen. Most crops require be­tween 10 and 20 pounds of sulfur per acre. As irrigation water approaches 5.0 ppm sulfate (see example calculation), crops receiving irrigation Win benefit in terms of sulfur nutrition. Most irrigation water in Southeast Missouri contains WQ278 •< 0.3 ~ <10 ~ 21 - 30 ~ 0.3 - 0.5 lliiUlUjJ 0.5 - 0.7 IgHHH - 20 lID11 • 31 - 51 Figure 7: Irrigation water sodium concetration Figure 8: Irrigation water electrical gradients (ppm) in southeast Missouri conductivity gradients (m/cm) in Southeast Missouri • Issued 'in furtherance of Cooperative Extension Work Acts of May 8 and June 30, 1914 rl-\lUniversity in cooperation with the United States Department of Agriculture. Gail L. Imig, qirector, Cooperative Extension Service, University of Missouri and Lincoln University, Columbia, UNIVERSITY OF MISSOURI Missouri 65211.• An equal opportunity institution.\...;,IExtension COLUMBIA New I March 1991/1OMWQ278 

Calculating crop nutrient value from irrigation water inputs : a survey of Southeast Missouri irrigation (1991)

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