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Considerations for More Efficient Nitrogen Management: San Joaquin Valley of California

R.B. Hutmacher, R.L. Travis, D.E. Rains, R.L. Nichols, B.A. Roberts, S.D. Wright, R.N. Vargas, B.H. Marsh, D.S. Munk, B.L. Weir, D.J. Munier, F. Fritschi, M.P. Keeley, and R.L. Delgado

ABSTRACT

Objectives in a five-year field study were to identify crop growth and yield responses to applied nitrogen (N) and provide in-formation to improve fertilizer N management using soil residual N estimates. Responses of Acala cotton (Gossypium hirsutum L.) to a range of applied nitrogen treatments were investigated in a multi-site experiment in California's San Joaquin Val-ley. Objectives Baseline fertilizer application rates for the lowest applied nitrogen treatments were based on residual soil nitrate-N (NO3-N) levels determined on soil samples from the upper 2 ft of soil collected prior to spring N fertilization and within about one to two weeks post-planting each year. Results have shown positive cotton lint yield responses to increases in applied N across the 50 to 200 lb N/ac range in only 41 percent (16 out of 39) of the test sites. Soil NO3-N monitoring to a depth of 8 feet in the spring (after planting) and fall (post-harvest) indicate most changes in soil NO3 occur within the upper 4 feet of soil. However, some sites (those most prone to leaching losses of soluble nutrients, water) also exhibited net increases in soil NO3-N in the 4 to 8 foot zone when comparing planting time versus post-harvest data. The lack of yield responses and soil NO3-N accumulations at some sites indicate that more efforts should be put into identifying the amount of plant N re-quirements that can be met from residual soil N, rather than solely from fertilizer N applications.





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Document last modified April 16, 2003