Effects of nitrogen rate and its basal to dressing ratio on uptake, translocation of nitrogen and yield in rice
氮肥用量与运筹对水稻氮素吸收转运及产量的影响

The effects of nitrogen rate and its basal to dressing ratio on the uptake, translocation of nitrogen and yield in rice were studied by using 15N isotope tracing in the micro-plot experiment. There were three N rates (0, 150, 240 kg/hm2 N, respectively) and two different fractions being applied, viz, A (40% at basal, 30% at 10 days after transplanting (DAT), 30% at 36 DAT) and B (30% at basal, 20% at 10 DAT, 50% at 36 DAT) for each N rate, which were expressed as N0, N150A, N150B, N240A and N240B, respectively. At the same time, the field experiment was conducted in the same field, and experimental design was same as that of the 15N isotope tracing experiment with three repetitions. 15N isotope tracing experiment showed that the amounts of nitrogen derived from fertilizer(Ndff) and soil(Ndfs) absorbed by rice and residual amount in the soil were significantly increased as the increase of nitrogen rate from 0 to 240 kg/hm2 N. Compared to other nitrogen rate treatment, more Ndff and Ndfs absorbed by rice and residual amount in the soil of 240 kg/hm2 N treatment at the maturity stage were found, which was 110.25, 65.91 and 32.69 kg/hm2 respectively. However, nitrogen recovery efficiency and residual amount in the soil was decreased, increasing in the unaccounted nitrogen rate. When nitrogen was applied at the same nitrogen rate in three splits as 30% basal, 20% 10 DAT, 50% 36 DAT, compared with the N splits as 40% basal, 30% 10 DAT, 30% 36 DAT, the amount of Ndff absorbed by rice was markedly increased, nitrogen recovery efficiency improved, the unaccounted nitrogen rate decreased at maturity stage. Appropriate nitrogen fertilizer rate with increasing topdressing nitrogen amount such as N240B treatment increased grain yield. In conclusion, under the condition of this experiment, as far as grain yield and environmental benefits are concerned, the most appropriate nitrogen fertilizer applying regime recommended is N240B treatment, its nitrogen fertilizer rate is 240 kg/hm2 N and 30% for basal, 20% for 10 DAT and 50% for 36 DAT.