Winter straw and water management effects on soil nitrogen dynamics in California rice systems

This study examines the effects of straw management and winter flooding on soil N dynamics and crop N uptake in California rice (Oryza sativa L.) systems. Experiments were established in two locations in northern California with main plot treatments being winter flooding or no flooding; and four straw management practices (burn, remove, incorporate, and roll) as subplot treatments. Fertilizer was applied to the plots at the recommended levels for each site, but within each plot a zero N microplot was established. Total straw inputs before winter flooding averaged 7000 kg ha(-1) for the incorporate and roll treatments, 4200 kg ha(-1) for the remove, and 1600 kg ha(-1) for the burn treatment (straw N ranged from 11 to 66 kg ha(-1)). Before flooding the field for planting, there was 9% less straw in winter flooded plots compared to nonflooded plots. Straw incorporation resulted in more rapid straw decomposition compared to other treatments where the straw was not incorporated. Furthermore, potentially mineralizable N and soil extractable N was higher in the winter flooded treatments and where rice straw was retained. Crop response varied between sites but our results suggest that N fertilizer recommendations could potentially be reduced by 20 kg ha(-1) if straw is incorporated and winter flooded.