Effects of Nitrogen Fertilizer Applications on Photosynthetic Production and Yield of Japonica Rice

Nitrogen management plays important roles in high-yielding rice production. In this two-year study, four rice cultivars were used to investigate the effects of the nitrogen application regime on yields, yield components, photosynthetic characteristics, and the dry matter accumulation and transformation of rice. Under a split-plot design, the main plots were assigned to five nitrogen application strategies, of which strategies 0 (N1), 165 (N2), 195 (N3), and 225 kg N ha−1 (N4) were applied as follows: 50% at basal, 35% at tillering and 15% at panicle initiation. In addition, strategy N5 was applied with 195 kg N ha−1 by 40% at basal, 15% at green-returning, 25% at the tillering stage, 15% at the panicle initiation stage, and 5% at the spikelet differentiation stage. Each main plot was sub-plotted by four experimental rice cultivars. Our results showed that all four cultivars obtained the highest yield with 195 kg N ha−1application. The nitrogen treatments seemed to have a smaller effect on the number of spikelets per panicle and 1000-grains weight, but more influence on the number of panicles and seed-setting rate and eventually affected grain yield. Under the N5 treatment, high yield was obtained due to more effective panicles, more spikelets per panicle and a high seed-setting rate. Additionally, the N5 treatment caused a longer leaf stay-green duration and higher photosynthetic potential, and the leaf area decreased slower at the late stage. The N4 treatment increased the dry matter formation at the jointing stage and the N3 treatment accelerated the dry matter accumulation between the jointing and heading stages. The results suggested that under 195 kg N ha−1 nitrogen amount, a higher post-anthesis biomass could be gained, and the N5 treatment showed greater advantages from heading to maturity than the other treatments in the aspects of more dry matter accumulation at the late growth stage, a coordinated organ growth ratio, and a higher matter translocation rate from the stem and leaf to the panicle, thus benefiting yield formation.