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This article in SSSAJ

  1. Vol. 31 No. 5, p. 672-675
    Received: Oct 27, 1966
    Accepted: June 30, 1967

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Predicting Nitrogen Availability to Rice: I. Comparison of Methods for Determining Available Nitrogen to Rice from Field and Reservoir Soils1

  1. J. L. Sims,
  2. J. P. Wells and
  3. D. L. Tackett2



Organic matter or available N in soil before or after incubation under waterlogged conditions each was used to predict soil N availability to ‘Nato’ rice (Oriza sativa L.) plants in a greenhouse experiment. The 42 silt loams had much lower organic matter and available N contents than the 19 clays (or reservoir soils) used in the study. Soluble + extractable NH4+-N after 6 days incubation accounted for 91% of the variation in yield on the 19 clay (or reservoir) soils, but accounted for only 18% on the 42 silt loams.

Initial NH4+-N, initial NO3-N, NH4+-N production during 6 days incubation, and NH4+-N production during 6 to 12 days incubation, as independent variables in a multiple linear regression, were used to predict grain yield. Little was gained by including NO3-N or 6 to 12 day NH4+-N production. Of the independent variables included, NH4+-N production during 0 to 6 days incubation alone accounted for the greatest percentage of yield variation but including initial NH4+-N together with 6 day NH4+-N production (also initial NH4+-N + that produced during 6 days) improved the prediction.

Organic matter or methods which measure total N in soil alone were poor predictors of N availability to rice. Organic matter accounted for 41 % of the variation in yield on clay soils and < 1% on silt loams, whereas total N accounted for 56 and < 1% of the yield variation on the clays and silt loams, respectively.

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