The Fate of Fertilizer Nitrogen Applied to the Paddy Field and Its Absorption by Rice Pl ant : I. Absorption of basal nitrogen by rice plant

Abstract

The efficiency and absorption of basal nitrogen (ammonium sulfate) enriched with 15N was studied in the paddy field in 1969 and 1970. Rice plant was transplanted at two different times, in early and late May, and was grown under the two rates of basal nitrogen, 60-70 kg/ha and 150 kg/ha. It was ascertained that the absorption of basal nitrogen by rice plant almost finished at the end of June in all the experimental plots. After that, the rice plant absorbed only soil nitrogen. The rate of plant absorption of fertilizer nitrogen was low soon after transplanting and increased gradually. The maximum rate was found in the early of June in the early-transplanted plots and in the middle of June in the late transplanted plots. According to nitrogen analysis at different growth stages, the ratios of the amounts of fertilizer nitrogen to those of total nitrogen absorbed by the plant were the highest soon after the transplanting and decreased gradually. They were higher in the plots with the high rate of basal nitrogen than those with the low rate. The recoveries of nitrogen in the plant which were calculated from the tracer were 22 per cent in 1969 and 26-27 per cent in 1970. On the other hand, the gross recoveries of nitrogen were ranged from 43 to 50 per cent in 1970. The ratios of the amounts of fertilizer nitrogen to those of total nitrogenoin the plant at maturity were about 25 per cent in the high nitrogen plots and less than 15 per cent in the low nitrogen plots. The amount of soil nitrogen absorbed by the plants was greater in the plots with basal nitrogen than in those without basal nitrogen. It was assumed that the effect of basal nitrogen contributud to the gross recovery of nitrogen in the plant which was substantially greater than the recovery calculated from the tracer.