Nitrogen transformation processes in relation to improved cultural practices for lowland rice |
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Authors: | S K De Datta |
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Institution: | 1. Agronomy Department, International Rice Research Institute, Los Ba?os, P.O. Box 933, Manila, Philippines
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Abstract: | Summary Inappropriate method and timing of N fertilizer application was found to result in 50–60% N losses. Recent nitrogen transformation
studies indicate that NH3 volatilization in lowland rice soils is an important loss mechanism, causing a 5–47% loss of applied fertilizer under field
conditions. Estimated denitrification losses were between 28 and 33%. Ammonia volatilization losses from lowland rice can
be controlled by i) placement of fertilizer in the reduced layer and proper timing of application, ii) using phenylphosphorodiamidate
(PPD) to delay urease activity in flooded soils, and iii) using algicides to help stabilize changes in floodwater pH.
Appropriate fertilizer placement and timing is probably the most effective technique in controlling denitrification at the
farm level. The effectivity of nitrification inhibitors as another method is still being evaluated.
With 60–80% of N absorbed by the crop derived from the native N pool, substantial yield gains in lowland rice are highly possible
with resources already in the land. Extensive studies on soil N and its management, and an understanding of soil N dynamics
will greatly facilitate the decrease in immobilization and ammonium fixation in the soil and the increase in N availability
to the rice crop. Critical research needs include greater emphasis on N transformation processes in rainfed lowland rice which
is grown under more harsh and variable environmental regimes than irrigated lowland rice. |
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Keywords: | Ammonia volatilization Denitrification Nitrogen Rice |
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