Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: November 7, 2004
Publication Date: June 1, 2005
Citation: Olk, D.C., Cassman, K.G., Anders, M.M., Schmidt-Rohr, K., Mao, J.D. 2005. Does anaerobic decomposition of crop residues impair soil nitrogen cycling and yield trends in lowland rice? [CD-ROM] Proceedings of the World Rice Research Conference, Nov. 4-7, 2004, Tokyo and Tsukuba, Japan. p. 374-377.
Double- and triple-cropping of irrigated lowland rice in tropical Asia has led to a substantial long-term yield decline in field experiments where initial yields were near the yield potential ceiling. The yield decline has been attributed partly to nitrogen (N) deficiency during reproductive crop growth stages. In recent studies of Philippine and Arkansas rice soils, an accumulation of phenolic compounds in soil organic matter coincided with decreased mineralization of soil N late in the season. The timing of N fertilizer applications was not adjusted accordingly in Arkansas, where yield decreased by 17%. Chemical analysis of a triple-cropped Philippine soil demonstrated the covalent binding of soil organic N by phenolic lignin residues. This anilide structure is recalcitrant and may release N to the rice crop only very slowly or upon field drainage and soil aeration. Such stabilization of soil N might be avoided through aerobic decomposition of crop residues. This hypothesis was tested by a four-year study in a Philippine rice field. Late-season N mineralization from young organic matter was significantly greater following aerobic decomposition than following the conventional anaerobic decomposition in flooded soil. Aerobic decomposition also promoted crop uptake of fertilizer N and prevented the accumulation of phenolic compounds in soil. The impact of decreased soil N availability on long-term rice yield trends in farmers' fields cannot currently be assessed due to an inadequate historical database of yields, fertilizer N inputs, and soil samples. Anaerobic decomposition of crop residues may reduce rice yield where initial yield levels are high, N availability is the primary yield-limiting factor, and all N fertilizer is applied pre-planting and/or during early growth stages. Future work will assess the benefits of aerobic decomposition to continuous rice and other anaerobic cropping systems where yield loss and nutrient deficiencies have also been reported: rice-wheat (Japan), taro (Hawaii), and no-till continuous maize (North America).