Delaying First Fertilization Time Improved Yield and N Utilization Efficiency on Direct Seeding Rice

Direct seeding rice (DSR) is a cost-saving and efficient production technology. It is of great significance to identify the characteristics of nitrogen demand of DSR in further improving yield and nitrogen use efficiency. In this study, a field experiment was carried out with inbred rice (HHZ) and hybrid rice (FLY4, YLY6) in Wuhan, China, in 2020 and 2021, respectively. Two fertilization ratios are as follows: basal fertilizer: tillering fertilizer: panicle fertilizer = 5:2:3 (T0); basal-tillering fertilizer: panicle fertilizer = 6:4. Four first fertilization time set as follows: T1, basal-tillering fertilizer was applied at 10 days after seeding (DAS); T2, basal-tillering fertilizer was applied at 15 DAS; T3, basal-tillering fertilizer was applied at 20 DAS; and T4, basal-tillering fertilizer was applied at 25 DAS. The changes of yield and yield components, above-ground biomass accumulation, nitrogen use efficiency, harvest index (HI), and leaf SPAD were investigated. The results showed that the yield of DSR could be significantly increased by properly postponing the first basal-tillering fertilization time. Compared with the T0, the basal-tiller fertilizer application at 20 DAS could significantly increase the yield by 15.1%, mainly because the number of spikelets per unit area increased by 18.9% on average across years and varieties. Delaying the first application time of basal-tillering fertilizer in DSR can significantly increase the biomass accumulation of above-ground leaves and stems and increase the yield, but with the decrease of HI in T3 and T4. In addition, delaying the first application time of basal-tiller fertilizer could also effectively improve the nitrogen use efficiency by 12.1% in DSR. The PFP and AE of T3 were significantly increased by 15.1% and 55.9% compared with T0, respectively. Delayed basal-tiller fertilizer treatment laid the foundation for maintaining higher leaf SPAD value in later developmental stage. To sum up, delaying the first application time of basal-tillering fertilizer was beneficial to build a better population of DSR, with high yield and nitrogen use efficiency, which has important reference significance for further optimization of light and simplified direct seeding nitrogen technology of rice. However, the delay of basal-tillering fertilizer application time leads to the increase of biomass, accompanied by the risk of plant lodging. Therefore, the optimal application amount of basal-tillering fertilizer needs to be further explored.