EFFICIENT MANAGEMENT OF SOIL AND BIOLOGICALLY FIXED NITROGEN IN INTENSIVELY – CULTIVATED RICE FIELDS

Abstract

A decline in productivity in wetland rice has been detected in some intensively-cultivated experimental farms in Asia since the early 1980s. Increased doses of fertilizer N are being used in both experimental farms fields to maintain the original yield levels. Little attention has been paid to judicious management of native soil N, which is the principle N source for rice, and to biological N fixation (BNF), which largely replenishes the soil N concentration. We review here various effects of long-term flooding and puddling associated with intensive cultivation of wetland rice on soil N availability and BNF. Some strategies are suggested to efficiently manage these two N sources to sustain high productivity of the rice lands.