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Nutrients applied to crops are usually in the form of commercial fertilizers, but manure is also used to fertilize the soil. An adequate supply of the nutrients, such as nitrogen, phosphorus, and potassium, and maintenance of proper soil pH are essential to crop growth (Esser, 1998). However, if these nutrients are supplied in excess environmental contamination can occur because the excess nitrogen can not be used by the plants and might leach into the ground. Nutrient management can help reduce nonpoint pollution by applying nutrients at the proper time, only applying the types and amounts of certain nutrients that are necessary to produce a crop, and taking into account the possible environmental dangers of the site. The goal of this management is to reduce nutrients draining from the edge of fields and minimize leaching of nutrients from the root zone (EPA, 1993). This management results in a reduction of the amount of fertilizers being applied to the land, which will reduce the cost of fertilizer for the farmer and protect surface and groundwater quality. Improving the efficiency of fertilizer use will improve the balance of nutrients in the land, reducing the amount of nutrients that will leach from the field to the waterways during the non-growing season.
In order to use a nitrate management plan farmers will need to perform soil testing for each field, soil/tissue testing during the early growth stages of the crop, and testing of manure, irrigation water, and sludge if they are used (EPA, 1993). Two of the most important ways to reduce the amount of fertilizers reaching the field are to reduce the fertilizer application rates and manage the timing of fertilizer application. Applying the proper amount of nitrogen fertilizer is critical to obtain a good yield, good grain quality, and solid profits. Even though using too much fertilizer can reduce the size of the yield, farmers tend to err on the liberal side of fertilizer use. The economics of overfertilization is why farmers tend to use too much fertilizer. According to Janet Pelley (1999), nitrogen costs only 18 cents a pound and may yield an extra bushel of corn worth $2.10. This excess nitrogen ranges between 22 and 67 kg/N/hectare (Legg et al., 1989). Thus, nitrogen applied in excess of crop need will lead to a dramatic increase in nitrate concentration (Mitsch, 1999). The nitrate that accumulates in the soil during dry periods is the major source of nitrate lost in tile drainage. Utilizing soil testing to determine how much nitrogen fertilizer to apply to the field will help reduce these high nitrate concentrations. Another good management plan for reducing fertilizer use is precision agriculture.
Managing the timing of nitrogen fertilizer application is the other main way to effectively manage nutrient levels in the field. Applying fertilizer in the spring results in a higher uptake of nitrogen by the growing crops. However, many farmers apply fertilizer in the fall because of lower prices, better field conditions, and the farmers have more time to apply the fertilizer to the field (National Research Council, pp. 40). The short window of time to apply fertilizer in the spring is the biggest problem with this management scheme because farmers do not have much time to apply fertilizer to the field when it will be most effective for crop growth. However, if the timing can be improved there should be a large reduction in the loss of nitrate to surface waters.
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