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This article in AJ

  1. Vol. 85 No. 5, p. 1061-1067
    Received: Sept 29, 1992

    * Corresponding author(s):
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Nitrogen Credits in Soybean-Corn Crop Sequences on Three Soils

  1. L. G. Bundy ,
  2. T. W. Andraski and
  3. R. P. Wolkowski
  1. Dep. of Soil Science, 1525 Observatory Dr., University of Wisconsin, Madison, WI 53706



Economic and environmental incentives to accurately predict corn (Zea mays L.) N requirements emphasize the need to assign appropriate N credits for soybean (Glycine max L.) in soybean-corn crop sequences. This study was conducted to determine corn response to N and N credits for soybean in crop sequences. The effects of corn-corn (CC), soybean-corn (SbC), and soybean-corn-corn (SbCC) crop sequences and applied N (0 to 225 kg N ha−1) on corn grain yield, N uptake, and oil NO3 and NH4 concentrations were determined for 4 yr at three sites differing in climatic and soil characteristics. Four-year mean yields in SbC were 1.4 and 2.2 Mg ha−1 higher than in CC at two sites with nonirrigated silt loam soils, but yield effects due to crop sequence were small on an irrigated sandy soil. Corn response to applied N varied markedly among the three sites and between years at the sites on silt loams oils. Mean corn N uptake in SbC was higher (51 kg N ha−1) than in CC on silt loam soils but not on the sandy soil. Soybean N credits estimated with a fertilizer replacement value (FRV) approach and from the difference in N rates at maximum yield in SbC and CC sequences (DNM) differed markedly among locations and years and ranged from − 22 to 210 kg N ha−1. Soybean provided little N to subsequent crops on sandy soils due to probable loss of residue N through leaching prior to use by the following crop. On silt loam soils, crop sequence effects on yield and N uptake indicate soybean N contributions to subsequent crops; however, fixed value N credits or N credits based on N response data combined over years will seldom accurately predict actual soybean N contributions. Site-specific diagnostic tests are needed to improve crediting of N supplied by soybean in crop sequences.

Research supported by the Wisconsin Fertilizer Res. Fund, the Wisconsin Soybean Marketing Board, and the College of Agricultural and Life Sciences, Univ. of Wisconsin-Madison.

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