Nitrogen Management on Dairy Farms
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Managing N Losses to Water from Agricultural Fields

Leaching is a pathway of N loss of a high concern for water quality. Soil particles do not hold on to nitrate very well because both are negatively charged. As a result, nitrate easily moves with water in the soil. The rate of leaching depends on soil drainage, rainfall, amount of nitrate present in the soil, and crop uptake. The EPA has set the maximum contaminant level for drinking water at 10 ppm N in the form of nitrate (US EPA, 2005; www.epa.gov/safewater/mcl.html#mcls).

In general, well-drained soils, unexpected low crop yield, high N inputs (especially outside of the growing season) and high rainfall are all conditions that increase the potential for nitrate leaching from the soil. In addition, fields with a thin layer of soil, regardless of drainage class, over fractured bedrock and coarse textured soil over aquifers have an elevated potential for leaching losses to groundwater. Improving N efficiency in field crop management can significantly reduce the loss of nitrate to ground- and surfacewaters. Strategies described in the previous pages of the Crop and Soil N Management section and summarized, below, will improve N use efficiency in field crop production. The following best management practices to reduce N leaching losses are based on research done by, among others, Sogbedji and coworkers (2000) and Van Es and coworkers (2002) and can be found in the New York Nitrate Leaching Index Manual (Czymmek et al., 2003).

Other findings and case studies for reducing N losses from fields to ground- and surfacewaters are found in the articles, below.

Manure and Groundwater Protection Guidelines

Supplemental Manure Spreading Guidelines to Reduce Water Contamination Risk During Adverse Weather Conditions

Impact of dairy farming on well water nitrate level and soil content of phosphorus and potassium.

Hutson, J. L., R. E. Pitt, R. K. Koelsch, J. B. Houser, and R. J. Wagenet. 1998. Improving dairy farm sustainability II: Environmental losses and nutrient flows. J Prod Agric. 11(2):233-239.

Sogbedji, J.M., H.M. van Es, C.L. Yang, L.D. Geohring, and F.R. Magdoff. 2000. Nitrate leaching and N budget as affected by maize N fertilizer rate and soil type. J. Environm. Qual.
29:1813-1820.

Van Es, H.M., K.J. Czymmek, and Q.M. Ketterings. 2002. Management Effects on N leaching and Guidelines for an N Leaching Index in New York. J. Soil Water Conserv. 57(6): 499-504.