Both N and P are needed by plants in large amounts, but when soils are too rich in these nutrients, they are environmental hazards. And although N and P behave differently in soils, most sound management practices for one are also sound for the other. Using soil tests (and for N on corn the end-of-season lower stalk nitrate test) and modern nutrient management planning that credits all sources, such as manures and decomposing sods, can help better manage these nutrients. Reduced tillage, cover crops, and rotation with sod crops decrease runoff and erosion and help in many other ways, including better N and P management.
Balkcom, K.S., A.M. Blackmer, D.J. Hansen, T.F. Morris, and A.P. Mallarino. 2003. Testing soils and cornstalks to evaluate nitrogen management on the watershed scale. Journal of Environmental Quality 32: 1015–1024.
Brady, N.C., and R.R. Weil. 2008. The Nature and Properties of Soils, 14th ed. Upper Saddle River, NJ: Prentice Hall.
Cassman, K.G., A. Dobermann, and D.T. Walters. 2002. Agroecosystems, nitrogen-use efficiency, and nitrogen management. Ambio 31: 132–140.
Jokela, B., F. Magdoff, R. Bartlett, S. Bosworth, and D. Ross. 1998. Nutrient Recommendations for Field Crops in Vermont. Burlington: University of Vermont, Extension Service.
Kay, B.D., A.A. Mahboubi, E.G. Beauchamps, and R.S. Dharmakeerthi. 2006. Integrating soil and weather data to describe variability in plant available nitrogen. Soil Science Society of America Journal 70: 1210–1221.
Laboski, C.A.M., J.E. Sawyer, D.T. Walters, L.G. Bundy, R.G. Hoeft, G.W. Randall, and T.W. Andraski. 2008. Evaluation of the Illinois Soil Nitrogen Test in the North Central region of the United States. Agronomy Journal 100: 1070–1076.
Magdoff, F.R. 1991. Understanding the Magdoff pre-sidedress nitrate soil test for corn. Journal of Production Agriculture 4: 297–305.
Melkonian, J., H.M. van Es, A.T. DeGaetano, J.M. Sogbedji, and L. Joseph. 2007. Application of dynamic simulation modeling for nitrogen management in maize. In Managing Crop Nutrition for Weather, ed. T. Bruulsema, pp. 14–22. Norcross, GA: International Plant Nutrition Institute Publication.
Mitsch, W.J., J.W. Day, J.W. Gilliam, P.M. Groffman, D.L. Hey, G.W. Randall, and N. Wang. 2001. Reducing nitrogen loading to the Gulf of Mexico from the Mississippi River basin: Strategies to counter a persistent ecological problem. BioScience 51: 373–388.
National Research Council. 1988. Nutrient Requirements of Dairy Cattle, 6th rev. ed. Washington, DC: National Academy Press.
Olness, A.E., D. Lopez, J. Cordes, C. Sweeney, and W.B. Voorhees. 1998. Predicting nitrogen fertilizer needs using soil and climatic data. In Procedures of the 11th World Fertilizer Congress, Gent, Belgium, Sept. 7–13, 1997, ed. A. Vermoesen, pp. 356–364. Gent, Belgium: International Centre of Fertilizers.
Sawyer, J., E. Nafziger, G. Randall, L. Bundy, G. Rehm, and B. Joern. 2006. Concepts and Rationale for Regional Nitrogen Guidelines for Corn. Iowa State University Extension Publication PM2015, 27 pp.
Sharpley, A.N. 1996. Myths about P. Proceedings from the Animal Agriculture and the Environment North American Conference, Dec. 11–13, Rochester, NY. Ithaca, NY: Northeast Region Agricultural Engineering Service.
van Alphen, B.J., and J.J. Stoorvogel. 2000. A methodology for precision nitrogen fertilization in high-input farming systems. Precision Agriculture 2: 319–332.
Vigil, M.F., and D.E. Kissel. 1991. Equations for estimating the amount of nitrogen mineralized from crop residues. Soil Science Society of America Journal 55: 757–761.
Wortmann, C., M. Helmers, A. Mallarino, C. Barden, D. Devlin, G. Pierzynski, J. Lory, R. Massey, J. Holz, and C. Shapiro. 2005. Agricultural Phosphorus Management and Water Quality Protection in the Midwest. Lincoln: University of Nebraska.