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This article in AJ

  1. Vol. 85 No. 6, p. 1186-1192
    Received: Mar 22, 1993

    * Corresponding author(s):
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Spring Nitrogen on Winter Wheat: II. A Flexible Multicomponent Rate Recommendation System

  1. Peter C. Scharf and
  2. Marcus M. Alley 
  1. Dep. of Crop and Soil Environmental Sciences, Virginia Polytechnic Inst. and State Univ., Blacksburg, VA 24061.



A recently developed system to predict the optimum N fertilizer rate for winter wheat (Triticum aestivum L. emend. Thell) at Zadoks growth stage (GS) 30 is based on the relationship between measured economic optimum N rate at GS 30 and wheat tissue N content measured at GS 30. However, winter wheat often needs an earlier application of spring N to achieve optimum yield. We therefore developed a test to determine which fields need this earlier (GS 25) application, and to predict the optimum N rate with split-application management using the tissue test or as a single spring application. The optimum N rate at GS 25 was measured over 5 yr, both with and without GS 30 N applications. These measured optimum N rates were regressed against a variety of possible predictor variables measured in the same fields. Tiller density at GS 25 was a good predictor of optimum N rate at GS 25 in a split spring application program. Using this relationship along with the GS 30 tissue test to make N recommendations for winter wheat increased estimated profit relative to using the tissue test alone. Soil NO3 measured to 0.9 m depth was the best predictor of optimum N rate at GS 25 when that is to be the only spring N application, and improved estimated profit relative to applying 90 kg N ha−1 at all sites; however, the economic performance of split spring N applications was substantially better than for any single spring applications. The recommendation system developed by integrating these component relationships is powerful and flexible, and provides field-specific N rate recommendations for all spring N applications to winter wheat, regardless of management decisions about splitting spring N applications.

Research supported in part by grants from the USDA-CSRS Water Quality Res. Program and the Virginia Div. of Soil and Water Conservation.

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