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This article in AJ

  1. Vol. 76 No. 6, p. 954-958
    Received: Sept 29, 1983



Nitrogen Utilization by Wheat from Residual Sugarbeet Fertilizer and Soil Incorporated Sugarbeet Tops1

  1. A. Abshahi,
  2. F. J. Hills and
  3. F. E. Broadbent2



Sugarbeet (Beta vulgaris L.) crops usually receive N fertilizer and sugarbeet tops are often returned to the soil following the harvest of storage roots. Residual sugarbeet fertilizer N and N in tops may reduce the amount of fertilizer N required for a subsequent crop. Field experiments at Davis, CA in 1980 and 1981 were designed to assess the contribution of these factors to a following wheat (Triticum aestivum L.) crop and to trace the partitioning of fertilizer N applied to sugarbeet, N in sugarbeet tops, and fertilizer N applied to the following wheat. The site was a Reiff loam, a deep alluvial coarse loamy soil with medium-textured substratum (Typic xerothents, Entisols, mixed, nonacid thermic). Sugarbeet, with and without 157 kg fertilizer N ha−1 and each with and without beet tops returned to the soil, were followed by wheat receiving four rates of fertilizer N (0, 62, 124, and 186 kg ha−1). The fertilizer used for both crops was stable, isotopically labeled 15N-depleted ammonium sulfate. Nitrogen from sugarbeet tops was traced in the wheat crop by returning sugarbeet tops containing labeled N to plots where sugarbeet had been fertilized with nonlabeled N and tops and storage roots removed. Residual sugarbeet fertilizer N was traced by additional plots of sugarbeet fertilized with more strongly labeled 15N-enriched ammonium sulfate. Of the 157 kg N ha−1 applied to the sugarbeet crop, 43% was taken up by tops and storage roots, 45% remained in the soil, primarily as organic N, leaving 12% not accounted for. Of the 45% (71 kg N ha−1) remaining in the soil only about 10% was taken up by the wheat crop, 66% remained in the soil, mostly as organic N, and 24% was not accounted for. When beet tops were returned to the soil, wheat straw and grain yield were maximid for this site with about 62 kg fertilizer N ha−1, but when tops were not returned, 124 kg fertilizer N ha−1 were required. From these applications, fertilizer N recovery by wheat was 82 and 61%, respectively. Sugarbeet tops contained, on average, 119 kg N ha−1 of which 27% was taken up by the wheat crop, 39% remained in the soil, mostly as organic N, leaving 34% not accounted for. Sugarbeet tops supplied the equivalent of 15 kg fertilizer N Mg−1 dry tops.

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