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

Abstract

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.