Adjusting harvesting time according to nitrogen application rate maximizes rice yield and nitrogen use efficiency.

Nitrogen (N) and harvest time are important factors in determining rice production potential. Elucidating reasonable N application rates and the relationship between N rate and harvesting time is necessary to maximize rice yield and efficiency. Two field trials were conducted with four N levels (0, 82.5, 165, and 247.5 kg N ha−1) and five N levels (0, 90, 180, 270, and 360 kg N ha−1) in Shayang (SY) and Wuxue (WX) counties, Hubei Province, respectively. Each was harvested at two time points (T1 and T2), at and after maturation, to investigate grain yield and N use efficiencies of rice. The results showed that the applied N and appropriately adjusted harvesting time significantly increased the grain yield, and compared with zero-N, the N additions increased rice yield by 3.7–26.9% and 8.4–22.5% for the SY and WX sites, respectively. However, with the increase of N application rate, the N use efficiency first increased and then decreased. Effects of harvest time on grain yield and N use efficiency vary with N application rates. At higher N levels, the appropriate delay in harvest time (T2) resulted in an increase in the 1000-grains weight and the rate at which grains were filled. Consequently, this led to an overall increase in grain yield. However, with zero or low N application rates, delayed harvest (T2) resulted in grain abscission, which decreased grain yield. In summary, applying N appropriately significantly increased the rice yield, and adjusting the harvesting time according to the N application rate further increased grain yield and N use efficiency. [ABSTRACT FROM AUTHOR]