Determining nitrogen topdressing rates in accordance with actual seedling density and crop nitrogen status in direct-seeded rice

BACKGROUND: Adjusting nitrogen (N) input based on actual seedling density (ASD) and plant N status is a practical approach for improving the yield stability of direct-seeded rice. However, the adjustment of topdressing N rates has been empirical in the past. This study aimed to establish a quantitative approach for determining N topdressing rates during tillering (N-til) and panicle development (N-PI) based on ASD and crop N status in direct-seeded rice. Field experiments were conducted involving 12 treatments, consisting of four N-til and three seeding rates in 2017, and eight treatments combining seeding rate, N-til, and N-PI in 2020. RESULTS: Linear regression analysis revealed that the tiller number at panicle initiation (TILPI) was predominantly influenced by ASD and N-til. The determination coefficients (R-2) of the regression models ranged from 0.887 to 0.936 across the four-season experiments. The results indicated that N-til could be determined accurately using ASD and the target maximum tiller number. Similarly, grain yield was influenced significantly by the N uptake at panicle initiation (NUPPI) and N-PI, with R-2 of 0.814 and 0.783 in the early and late seasons of 2020, respectively. This suggested that N-PI could be calculated based on NUPPI and the target grain yield. CONCLUSION: The findings offer a quantitative method for establishing N topdressing rates for tillering and panicle development, relying on the monitoring of actual seedling density and plant N status in direct-seeded rice production. (c) 2023 Society of Chemical Industry.