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Agronomy Journal Abstract -

Relative Efficiency of Applied N and Soil Nitrate for Winter Wheat Production1


This article in AJ

  1. Vol. 75 No. 1, p. 49-52
    Received: Jan 5, 1982

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  1. V. A. Haby,
  2. C. Simons,
  3. M. S. Stauber,
  4. R. Lund and
  5. P. O. Kresge2



The fertilizer N recommendation for a given yield of dryland winter wheat (Triticum aestivum L.) is lowered by the amount of nitrate-nitrogen (NO3-N) measured in the upper 1.2 m soil profile. This implies that soil NO3-N substitutes for fertilizer N on an equal basis. The study was designed to compare the effectiveness of soil NO3-N in the 1.2 m depth with fertilizer N for wheat production. Data were from 19 siteyears of N, P, and K rate combinations in 23 treatments planned to fit the nested-cube statistical design. A response function for grain yield was estimated using fertilizer N, P, and K, soil NO3-N, P, and water plus seasonal (April-July) precipitation in a nonlinear regression model. All explanatory variables except fertilizer N and soil NO3-N were set at fixed values to derive the yield response function. Marginal rates of substitution (MRS) of soil NO3-N for fertilizer N were derived from representative yield levels. Results indicate that soil NO3-N in the 1.2 m surface depth is not as efficient (approximately one-third) as fertilizer N for grain production. Substantial differences in economic returns exist between comparisons of fertilizer recommendations made using the response surface vs an accepted one-to-one substitution. Differences are greatest in the range of 75 to 150 kg of soil NO3-N/ha; the maximum difference, $44.36/ha occurs at a NO3-N level of 100 kg/ha. Additional research is needed on the N supplying ability of soil NO3-N for plant growth based on its zones of concentration within the soil profile.

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