Managing Agricultural Fertilizer Application to Prevent Contamination of Drinking Water

Source Water Protection Practices Bulletin Managing Agricultural Fertilizer Application to Prevent Contamination of Drinking Water If improperly managed, elements of fertilizer can move into surface water through field runoff or leach into ground water. The two main components of fertilizer that are of greatest concern to source water quality (ground water and surface water used as public drinking water supplies) are nitrogen (N) and phosphorus (P). This fact sheet focuses on the management of agricultural fertilizer applications; see the fact sheets on managing agricultural pesticide use, animal waste, and storm water runoff for other prevention measures that relate to agriculture. Inside this issue: Why is it Important to 2 Manage Fertilizer Use? Available Prevention 3 Measures Additional Information 6 Fertilizer and Fertilizer Use Facts: The Nitrogen and Phosphorus in fertilizer are the greatest concern to source water quality. 25% of all preplant N applied to corn is 1 - Fertilizer tractor. lost through leaching or dentrification. 60-90% of P moves with the soil. Consumption of nitrates can cause “blue Fertilizer Use in Agriculture baby syndrome”. Fertilizer application is waters. While fertilizer Nitrate has a drinking water MCL of required to replace crop efficiency has increased, 10mg/l. land nutrients that have Colorado State University Nutrient management abates nutrient been consumed by estimated that about 25 movement by minimizing the quantity of previous plant growth. It is percent of all preplant nutrients available for loss. essential for economic nitrogen applied to corn is yields. However, excess lost through leaching Fertilizer applied in the fall causes ground fertilizer use and poor (entering ground water as water degradation. Partial application in application methods can nitrate) or denitrification the spring can improve N uptake. cause fertilizer movement (entering the atmosphere Ammonium N fertilizers are not subject to into ground and surface as nitrogen gas). immediate leaching, but convert to nitrate. Page 2 Source Water Protection Practices Bulletin Why is it Important to Manage Fertilizer Use Near Sources of Drinking Water? Improper or excessive use of fertilizer Blue Baby Syndrome Effects can lead to nitrate pollution of ground or surface water. Nitrogen fertilizer, whether organic or inorganic, is bio- logically transformed to nitrate that is highly soluble in water. In this soluble form, nitrate can readily be absorbed 2 - Healthy and used by plants. On the other hearts. hand, soluble nitrate is highly mobile and can move with percolating water out of the soil, thus making it unavail- able for plant uptakes. Crop producers, therefore, need to match nitrogen applications to crop uptake to minimize nitrate leaching and maximize efficiency. Use of nitrogen-containing fertilizers can contribute to nitrates in drinking water. Consumption of nitrates can cause methemoglobinemia (blue baby syndrome) in infants, which reduces the ability of the blood to carry oxygen. If left untreated, methemoglobinemia can be fatal for affected infants. Due to this health risk, EPA set a drinking water maximum contaminant level (MCL) of 10 milligrams per liter (mg/l) or parts per million (ppm) for nitrate measured as nitrogen. Another major component of fertilizer is phosphorus. Under certain condi- 4 - Hypoplastic left heart syndrome. tions phosphorus can be readily trans- ported with the soil. In fact, 60 to 90 3 - dextro-Transposition of the great arteries, dTGA. percent of phosphorus moves with the Oxygenated blood shown in dark pink (above left) soil. Phosphorus is the major source of water quality impairments in lakes nationwide. Even though regulations that affect the taste and odor of water are not Federally enforceable under the Safe Drinking Water Act, munici- palities often must treat their drinking water supplies for these aesthetic reasons. The use of organic nutrient sources, such as manure, can supply all or part of the nitrogen, phosphorus, and po- tassium needs for crop production. However, organic fertilizers can also cause excessive nutrient loads if improperly applied. 5 - Tricuspid atresia 6 - Tetralogy of Fallot. Source Water Protection Practices Bulletin Page 3 Available Prevention Measures to Address Agricultural Applications of Fertilizer This section discusses some of the tential source of contamination, the nutrients available for loss. This is most often used prevention meas- purpose, cost, operational, and main- achieved by developing a compre- ures, but is not an exhaustive list of tenance requirements of the meas- hensive nutrient management plan all known measures. For information ures, the vulnerability of the source and using only the types and on additional prevention measures, water, the public’s acceptance of the amounts of nutrients necessary to see the documents referenced in the measures, and the community’s de- produce the crop, applying nutrients last section of this fact sheet. Please sired degree of risk reduction. at the proper times and with proper keep in mind that individual preven- The goal of these prevention meas- methods, implementing additional tion measures may or may not be ures is to minimize nutrient losses farming practices to reduce nutrient adequate to prevent contamination of from agricultural lands occurring by losses, and following proper proce- source waters. Most likely, individual edge-of-field runoff and by leaching dures for fertilizer storage and han- measures should be combined in an from the root zone. Effective nutrient dling. overall prevention approach management abates nutrient move- that considers the nature of the po- ment by minimizing the quantity of Fertilizer Application Timing Comprehensive Nitrogen fertilizer applications Nutrient should be timed to coincide as Management closely as possible to the period of Plans include maximum crop uptake. Fertilizer soil sampling, applied in the fall has been shown to cause ground water degrada- crediting other tion. Partial application of fertilizer sources of in the spring, followed by small nutrients and additional applications as needed, limiting can improve nitrogen uptake and fertilizer use. reduce leaching. Reasons to alter nitrogen amounts include abnormal weather or crop quality. 7, 8, 9, 10 - Seasons. Application Rates and Fertilizer Types One component of a comprehensive manure, and organic matter all con- the leaching potential is moderate to nutrient management plan is to de- tribute nitrogen to the soil, while or- high. In these situations, ammonium termine proper fertilizer application ganic matter and manure contribute nitrogen fertilizers should be used rates. The goal is to limit fertilizer to phosphorus. because they are not subject to imme- an amount necessary to achieve a Along with soil samples and fertilizer diate leaching. However, ammonium realistic yield goal for the crop. Soil credits from other sources, nitrogen nitrogen transforms rapidly into nitrate sampling and crediting other sources fertilizer recommendations are based when soils are warm and moist. More are also parts of the concept. on yield goals established by the slowly available nitrogen fertilizers Yearly soil sampling is necessary for crop producers. Yield expectations should be used in these conditions. determining plant nutrient needs and are established for each crop and Nitrification inhibitors can also delay to make accurate fertilizer recom- field based on soil properties, avail- the conversion of ammonium to ni- mendations. Many factors must be able moisture, yield history, and trate under certain conditions. considered when determining sam- management level. Phosphorus fertilizer is less subject to pling methods and frequency. Applying the appropriate form of ni- leaching, but loss through surface Calculating the optimal rate of appli- trogen fertilizer can reduce leaching. runoff is more common. To minimize cation also includes crediting other Nitrate forms of nitrogen fertilizer are losses of phosphorus fertilizer, appli- sources that contribute nitrogen and readily available to crops, but are cations should only be made when phosphorous to the soil. Previous subject to leaching losses. Nitrate needed (determined through soil legume crops, irrigation water, fertilizer use should be limited when testings) and at recommended rates. Page 4 Source Water Protection Practices Bulletin Fertilizer Application Methods Fertilizer application equipment recovered by the crop more effi- into surface water when excess should be inspected at least once ciently. All surface-applied fertilizers water is applied to fields. Irrigation annually. Application equipment should be mechanically incorporated systems, such as sprinklers, low- must also be properly calibrated to into the soil to reduce losses through energy precision applications, insure that the recommended surface runoff and volatilization. Fer- surges, and drips, allow producers to amount of fertilizer is spread. tilizer should never be applied to fro- apply water uniformly and with great Correct fertilizer placement in the zen ground, and also should be lim- efficiency. Efficiency can also be im- root zone can greatly enhance plant ited on slopes and areas with high proved by using delivery systems nutrient uptake and minimize runoff or overland flow. such as lined ditches and gated pipe, losses. Subsurface applied or incor- Irrigation water should be managed as well as reuse systems such as porated fertilizer should be used to maximize efficiency

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