Nitrogen dynamics and management in rice-legume cropping systems

This chapter reviews nitrogen (N) dynamics in lowland rice fields with emphasis on how N dynamics are influenced by typical soil drying and wetting cycles, the influence of legumes on soil N transformations and N accretion in rice-based cropping systems, the N contribution of legumes to rice, and the integrated management of legume N and industrial fertilizer N for rice. Most research on N contributions from legumes in the tropics has been focused on short-duration legumes grown and subsequently incorporated solely as green manures immediately before the monsoon rice crop. Nitrification during nonflooded periods among rice crops and then subsequent denitrification when soil is flooded for rice may be an important avenue for N loss. The N contribution of legumes in lowland rice-legume sequences, as in upland crop-legume sequences, depend on the quantity of legume N derived from N2 fixation, the NHI, the proportion of legume N mineralized, and the efficiency of use of this mineralized N by the succeeding crop. © 1991, Academic Press Inc.