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This article in AJ

  1. Vol. 63 No. 1, p. 48-51
    Received: May 9, 1970

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Laboratory Methods for Estimating Plant Available Nitrogen in Soil1

  1. J. A. Ryan,
  2. J. L. Sims and
  3. D. E. Peaslee2



Biological and chemical methods for obtaining an index of soil N availability to a test crop under different levels of N fertilization were evaluated on 15 Kentucky soils having a range of organic matter contents of 0.72 to 2.79%. Organic matter, N mineralized during aerobic incubation at 30C or 40C for 7 or 14 days, and extractable NH4+-N after incubation under waterlogged conditions for 7 or 14 days at 30C and 14 days at 40C were all significantly related to N uptake and relative increase in N uptake by ‘X-1605’ grain sorghum (Sorghum vulgares) during 18 weeks of growth in the greenhouse.

When the soils were amended in the laboratory with P and K or P, K, and Ca and incubated under waterlogged conditions, the relationship between extractable NH4+-N and N uptake by sorghum improved greatly over unamended soils. Nitrogen mineralized during aerobic incubation and NH4+-N after incubation of amended soil under waterlogged conditions were among the better predictors of both N uptake and relative increase in N uptake.

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