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This article in SSSAJ

  1. Vol. 52 No. 5, p. 1394-1398
     
    Received: Apr 2, 1987


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doi:10.2136/sssaj1988.03615995005200050035x

Nitrogen Use Efficiency and Nitrogen Budget for Conservation Tilled Wheat

  1. R. R. Sharpe ,
  2. L. A. Harper,
  3. G. W. Langdale and
  4. J. E. Giddens
  1. USDA-ARS, P.O. Box 87, Byron, GA 31008
    USDA-ARS, Watkinsville, GA 30677
    Dep. of Agronomy, Univ. of Georgia, Athens, GA 30602

Abstract

Abstract

The understanding of nitrogen (N) cycling in the soil-plant-atmosphere is necessary to maximize N use efficiency and to develop N budgets for wheat (Triticum aestivum L.) production. The objectives of this study were to determine the relative uptake rates of residual soil N and fertilizer N in conservation tilled winter wheat. These data were combined with soil mineralization and aerial NH3 flux data to present a N budget for the soil-plant-atmosphere system. Fertilizer N uptake was determined using ammonium nitrate (15NH415NO3) tagged with 3.78 atomic % 15N. The buried polyethylene bag technique was used to determine N mineralization. Fertilizer N uptake and N mineralization rates were determined four times during the spring growing season. Amounts of NH4 and NO3 in the top 0- to 300-mm soil layers were determined biweekly. Fertilizer N levels in the surface to 75-mm soil layers decreased rapidly due to plant uptake and immobilization. Of the N fertilizer utilized by the plants, 61% was absorbed in the first 28 d after application. During early vegetative growth stages (Feekes stages 3–5), fertilizer N uptake was 1.33 kg ha−1 d−1. During the elongation stage (Feekes stages 5–8), however, fertilizer N was immobilized and uptake of fertilizer N ceased. This resulted in a period of soil N insufficiency which was associated with atmospheric NH3 influx to the plants. After 4 to 5 wk, mineralization of fertilizer N became apparent and fertilizer N uptake rates increased until harvest. Influx of atmospheric N was small but total NH3 efflux from the soil-plant system was 15.5 kg N ha−1. About 21% of the spring applied fertilizer N was lost through NH3 volatilization and losses of this magnitude need to be considered in N balance studies. Placement of fertilizer N below the surface soil layer may decrease immobilization and increase plant uptake of N.

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