Transformation of soil and fertilizer nitrogen in paddy soil and their availability to rice plants

Summary A pot experiment in the field showed that addition of ammonium sulfate increased the uptake of soil nitrogen. A-value was found to be independent of the rate of nitrogen application. The rice plant took up about 13 percent of the nitrogen in rice straw which was incorporated into the soil when nitrogen fertilizer was not added, and about 15 percent when 50 ppm N was added. Addition of different levels of fertilizer did not affect the release of immobilized fertilizer nitrogen. Recovery of fertilizer by the rice plant was low when nitrogen was added as basal (broadcast). Recovery was improved by incorporating fertilizer nitrogen before transplanting. Recovery of fertilizer nitrogen when topdressed at reproductive stages was much higher than when applied as basal. A fairly large portion of fertilizer nitrogen was immobilized into the soil. Availability of immobilized nitrogen in the soil appeared low. re]19751117