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This article in AJ

  1. Vol. 79 No. 5, p. 937-943
     
    Received: Nov 21, 1986


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doi:10.2134/agronj1987.00021962007900050037x

Comparison of Organic and Inorganic Nitrogen Sources for Rice1

  1. M. P. Westcott and
  2. D. S. Mikkelsen2

Abstract

Abstract

Rice (Oryza sativa L.) responds well to green manure-N under flooded conditions, but more quantitative data are needed for comparisons to inorganic N. This study compared the effects of vetch (Vicia benghalensis L.) and (NH4)2SO4 on patterns of N availability and plant uptake, applied-N recovery at harvest, and grain yield in flooded rice culture. The sources were incorporated in a Clear Lake clay (Typic Pelloxerert) in factorial combination of 60 kg N/ha increments up to a maximum rate of 180 kg N/ha. Grain yields were determined in plots of 18.9 m2 while N balance was assayed in microplots (0.27 m2) treated with 15N-labeled materials. Ammonium sulfate was more effective in raising extractable-N concentrations early in the growing season and made a greater contribution to plant N status throughout the season. There was no evidence that vetch extended the period of N availability to plants. Grain yields were highly dependent on N uptake; they maximized at 10.1 Mg/ha with 120 kg N/ha as (NH4)2SO4 but responded linearly to vetch up to 8.4 Mg/ha with the highest rate of addition. Ammonium sulfate effected greater labeled-N recovery (19% across rates) and apparent N recovery (55.6%) by plants than vetch (10.1 and 27.9%, respectively). More vetch-N was recovered in the soil at harvest; total recoveries were, therefore, not significantly different between N sources. The rate of green manure-N mineralization early in the growing season appears to be the limiting factor in comparison to inorganic N.

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