Abstract
This study was conducted to obtain basic data to establish simple models of nitrogen dynamics for managing highly productive and environment-friendly low nitrogen application in rice production. Here, the amounts of nitrogen in percolating and overflowing water were investigated, and the nitrogen balance sheet was analyzed using 1/2000a Wagner pots and two rice cultivars, Koshihikari and Takanari. The fertilizer was applied by basal application and/or top-dressing at panicle initiation. The amounts of nitrogen mineralized before the maturity stage, supplied by rainfall and irrigation, and the amounts of percolated, overflowing, and absorbed by the rice plant, were 0.66, 0.06—0.08, 0.23—0.31, 0.00, and 0.51—1.27g per pot, respectively. The amounts of nitrogen loss and absorbed by the rice plant, were not significantly influenced by the nitrogen-application methods in either cultivar. In the nitrogen-application plot, 12—16% of nitrogen-input was lost by percolation, and most of it was soil nitrate nitrogen which was lost within ten days after flooding. Generally not a little fertilizer nitrogen was lost by percolating or overflowing in the paddy field. In this experiment, however, most of the basal nitrogen was denitrificated or adsorbed by the soil with a high clay content, most of the top-dressed nitrogen was absorbed by the rice plant, and there was no significant overflow by heavy rains. Therefore, only about 5% of fertilizer nitrogen was lost by percolation and overflowing.
