EFFECT OF WATER AND FERTILIZER MANAGEMENT ON NITROGEN-FIXATION (C2H2 REDUCTION) ASSOCIATED WITH RICE RHIZOSPHERE

The influence of fertilizer and water management schedules on the nitr ogenase activity associated with rice rhizosphere was investigated dur ing the dry season in experimental plots at two sites. Field plots wit h a high percolation rate (8.0 mm day(-1)) and high sand (33%) content supported higher rhizosphere nitrogenase activity under continuous fl ooding than under intermittent flooding. Nitrogenase activity decrease d marginally with an increase in the fertilizer N level. In field plot s with a lower percolation rate (2.3 mm day(-1)) and lower sand (26%) content, intermittent flooding supported better nitrogenase activity t han continuous flooding. The split application of N had little effect on the nitrogenase activity in this soil. Results suggest that, in add ition to fertilizer level and water regime, soil percolation rate and sand content can affect the rhizosphere-associated nitrogenase activit y.