Although drawbacks may include an increase in weed and pest occurrence, residue incorporation has not reduced yields as compared to burning at the long-term UC research sites. As one would expect, straw residue contains N which can be available for use by subsequent rice crops. Nitrogen is made available in the following ways:
Fertilizer N typically supplies about one-half of the annual requirement of a rice crop while the remainder is supplied by the mineralization of organic forms of N.
- Anaerobic decomposition serves to preserve residual N via the immobilization and sequestration of N by microorganisms.
- After several years of straw incorporation, soil organic matter may accumulate and ultimately supply N via mineralization processes.
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Click here for an illustration on nitrogen cycling.
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Horwath and van Kessel (1998) monitored large-scale experimental plots of varying rice straw residue treatments including:
burning,
- incorporation,
- winter flooding, and
- winter fallow without flooding
in fields at Biggs and Maxwell, CA. One experiment compared yields of two treatments:
no fertilizer N with straw incorporation, and
- no straw incorporation with varying fertilizer N applications.
When the latter group received 30 kg N/acre, grain yields were similar between that treatment and the incorporated/no fertilizer N treatment. This suggests that the overall N effect of straw incorporation is about 30 kg N/acre. Although this is one year's data from one site, this may be helpful in readjusting fertilizer N concentrations on straw-incorporated fields.
Finally, straw incorporation and winter flooding were experimentally demonstrated to be beneficial in providing nitrogen (N) for subsequent rice crops. These two alternative techniques, when combined, retain and provide more inorganic N than any other combination such as straw burning and non-flooded winter fallow.
Literature Cited
Horwath, W.R. and C. van Kessel. 1998. Reassessing soil N availability and fertilizer recommendations under alternative rice residue management practices. Annual Report, Comprehensive Rice Research 1998, University of California and U.S. Department of Agriculture.
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