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This article in AJ

  1. Vol. 103 No. 4, p. 1026-1035
    Received: Nov 15, 2010

    * Corresponding author(s): dan.jaynes@ars.usda.gov
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Economically Optimal Nitrogen Rates of Corn: Management Zones Delineated from Soil and Terrain Attributes

  1. Dan B. Jaynes *,
  2. Thomas C. Kaspar and
  3. Tom S. Colvin
  1. USDA-ARS, National Lab. for Agriculture and the Environment, Ames, IA 50011. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also be suitable


Much of the NO3 found in streams in the Midwest comes from leaching of N fertilizers applied to corn (Zea mays L.). To reduce this leaching, N fertilizer must be used more effectively. Dividing fields into areas that respond more uniformly to management is one approach for improving N fertilizer use. The objective of this study was to determine and compare economically optimal N fertilizer rates for corn in a corn–soybean [Glycine max (L.) Merr.] rotation within management zones. A method based on soil and landscape characteristics was used to divide three fields into management zones roughly equivalent to toeslope, footslope, backslope, and shoulder landscape positions. We applied N fertilizer at six rates within replicated small plots (15.1 by 4.5 m) located within each management zone. Yield vs. N rate for each management zone was fitted to the Mitscherlich equation using nonlinear methods. Final Mitscherlich parameters, economically optimal N rates, and their confidence limits were computed for each management zone. Yields at the highest N rate generally followed the pattern of toeslope ≥ footslope ≥ backslope >> shoulder among the management zones. Conversely, economically optimal N rates followed the reverse pattern and varied from 23 to 247 kg ha−1. Thus, yield at the highest N rate was a poor predictor of the optimal N rate for the management zones delineated in this study and N fertilizer application would have been optimized by applying relatively less to the toeslope and footslope management zones and relatively more to the shoulder and backslope management zones.

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