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This article in AJ

  1. Vol. 69 No. 2, p. 303-308
     
    Received: Aug 30, 1976


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doi:10.2134/agronj1977.00021962006900020025x

Residual Nitrate and Mineralizable Soil Nitrogen in Relation to Nitrogen Uptake by Irrigated Sugarbeets1

  1. George Stanford2,
  2. J. N. Carter3,
  3. D. T. Westermann3 and
  4. J. J. Meisinger2

Abstract

Abstract

Previously reported studies on N fertilization of sugarbeets (Beta vulgaris L.) in southern Idaho revealed considerable variation among sites in amounts of residual soil NO3 and N mineralized during short-term laboratory incubations. Consequently, the amount of N fertilizer needed to achieve near-maximum yields of sucrose differed markedly. The purpose of this study was to determine the feasibility of estimating amounts of N mineralized in the root zone during the season, taking into account site variations in temperature and soil water regimes. Residual soil NO3--N and mineralizable N to approximate rooting depth were estimated for 21 field sites in 1971 and six sites in 1972. The relative contributions of these two N sources to total N uptake by the crop, in the absence of applied fertilizer N, were then assessed. Estimates of N mineralized in the upper 45-cm soil layer for each successive month, ΔN, over a 6-month period were derived using the expression, ΔN/ Δt = kWN (k = fraction of N mineralized during each month, Δt, adjusted for average air temperature; and W = the estimated soil water content expressed as a fraction of the available water storage capacity). Resulting estimates of the fraction of potentially mineralizable N converted to (NO3- + NH4-)-N between 1 April and 30 September ranged from 0.15 to 0.22 (mean ± S.D. = 0.18 α 0.02) in 1971 and 1972. On the average, mature sugarbeets recovered about 73% of the estimated N mineralized (6 months) plus residual NO3--N. The relative contributions of these two sources of soil derived N, respectively, were approximately 66 and 75%, as estimated from multiple regression analyses.

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