Determining nitrogen topdressing rates in accordance with actual seedling density and crop nitrogen status in...

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.

Linear regression analysis revealed that the tiller number at panicle initiation (TIL_PI ) was predominantly influenced by ASD and N_til . The determination coefficients (R² ) 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 (NUP_PI ) and N_PI , with R² 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 NUP_PI and the target grain yield.

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. © 2023 Society of Chemical Industry.