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.