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This article in AJ

  1. Vol. 76 No. 1, p. 31-35
    Received: Jan 26, 1983

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Effect of Applied and Residual P on Double-Cropped Wheat and Soybean under Conservation Tillage Management1

  1. R. R. Sharpe2,
  2. J. T. Touchton3,
  3. F. C. Boswell2 and
  4. W. L. Hargrove2



In the Piedmont area of Southeastern USA, the economic advantages of double-cropped wheat (Triticum aestivum L. Thell) and soybean (Glycine max L. Merr.) have recently resulted in increased acreage of both crops. In many cases, the rotation is wheat and soybean under conservation tillage management. Many soils in this region of the USA are low in P, and it may be advantageous to raise these soils to the high soil test range before initiating conservation tillage practices. The purposes of this study were to determine if it is necessary to raise low P soils to the high soil test range prior to initiating conservation tillage systems and to determine how long a single high rate of P will maintain yields equal to those obtained with annual or biannual applications. Wheat and soybean were double-cropped under conservation tillage management on a Cecil sandy loam soil (clayey, kaolinitic Typic Hapludult) from 1978 to 1981. The P treatments were applied as a one-time application in the fall of 1977. Broadcast rates of P were 0,64, 128,256, and 384 kg ha−1. Two annual P applications of 64 kg P ha−1 were also included for comparison of residual soil P and annually applied P. One-time applications of 128 or more kg P ha−1 provided sufficient soil P to maintain soybean yields significantly higher than the zero P application rate 4 years after application. The 128 kg P ha−1 treatment also produced consistently good wheat yields for 3 years after application, but the 256 and 384 kg P treatments reduced wheat yields in 1978 due to increased lodging and glume blotch ((Sepforiu nodorum(). The data indicate that a single application of 128 kg P ha−1 can maintain wheat and soybean yields for at least 3 years in a double-cropping conservation tillage system without significantly reducing micronutrient uptake. Phosphorus fertilization increased soil P levels and plant tissue P. Applied P increased extractable soil Zn, but decreased the concentration of Zn, Cu, and Mn in the soybean plant tissue.

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