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This article in SSSAJ

  1. Vol. 57 No. 3, p. 750-756
    Received: Feb 27, 1992

    * Corresponding author(s):
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Tillage Effects on Legume Decomposition and Transformation of Legume and Fertilizer Nitrogen-15

  1. J. J. Varco ,
  2. W. W. Frye,
  3. M. S. Smith and
  4. C. T. MacKown
  1. Dep. of Agronomy, Mississippi State Univ., Mississippi State, MS 39762
    (USDA-ARS) Dep. of Agronomy, Univ. of Kentucky, Lexington, KY 40546-0091



The inclusion of legumes in cropping systems raises questions about their effectiveness as a N source. The objective of this study was to determine the effects of tillage on legume cover crop decomposition and transformation dynamics of legume and fertilizer 15N. Nitrogen-15-labeled hairy vetch (Vicia villosa Roth.) residue or fertilizer was added to soil cores contained in open-ended Plexiglas tubes placed in the field. Vetch residues were either placed on the soil surface for notillage (NT), or mixed with the soil for conventional tillage (CT). In 1984, 15NH415NO3 was applied at rates of 0 and 100 kg N ha−1 and, in 1985, (15NH4)2SO4 was applied at rates of 0 and 150 kg N ha−1 to both NT and CT cores with a history of winter fallow. Fertilizer 15N was applied in solution to the soil surface. Within 30 d, 77% of the original vetch residue weight was lost with CT, compared with 45% with NT. Nitrogen lost from the residue by 30 d averaged 89% with CT and 60% with NT. At 15 d in 1985, soil inorganic 15N recovery for fertilizer was 78% with CT and 57% with NT, and for vetch it was 47% with CT and 12% with NT. Vetch 15N immobilization averaged 2.3 times greater than fertilizer 15N with CT and 1.7 times greater with NT. The results indicate that N availability as measured by soil inorganic N is less from vetch residue than fertilizer due to both greater vetch N immobilization and the dependence of vetch N mineralization on decomposition rate.

Contribution from the Dep. of Agronomy and USDA-ARS, Kentucky Agric. Exp. Stn. Journal Paper no. 92-3-236.

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