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Soil Science Society of America Journal Abstract -

Residual Effects of 15N-Labeled Fertilizers in a Field Study1


This article in SSSAJ

  1. Vol. 36 No. 1, p. 91-94
    Received: May 24, 1971
    Accepted: Aug 27, 1971

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  1. R. L. Westerman and
  2. L. T. Kurtz2



Residual effects of two 15N-labeled N fertilizers, urea and oxamide, were compared during the second cropping season after they had been applied at rates of 0, 56, 112, and 168 kg N/ha. ‘Sudax SX11’ sorghum-sudan grass hybrid (Sorghum sudanense) was grown and harvested three times during this second cropping season while the residual effects were being measured.

Fertilizer N removed in plant tops during this second year of cropping contained 13–18% of the residual fertilizer N in the soil at the end of the first season and was equal to 4–6% of that applied originally in the fertilizers. At the end of the second cropping season, 22 and 26% of the initial applications of N in urea and oxamide, respectively, remained in the soil. The effect of carriers on these amounts of residual fertilizer N was not significant. The removals in crops during the second season plus those amounts remaining in the soil at the end of the second season were essentially equal to the residual fertilizer N which had been in the soil at the end of the first season. Thus, no evidence was found for loss of residual N by leaching, denitrification, or other processes during the second cropping season. Since removals of N in crops were considerably greater than the additions in fertilizers, it is hypothesized that nearly all inorganic fertilizer N was taken out of the soil and most of the residual fertilizer N was in relatively stable organic forms. Conditions for these experiments had been selected to conserve N, and as a consequence the deficits of fertilizer N reported here may be expected to be smaller than might occur under other practices.

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