Nitrogen/potassium interactions increase rice yield by improving canopy performance

The interactions between nitrogen (N) and potassium (K) are important determinants of rice yield, but the mechanisms involved remain poorly understood. For example, N/K interactions may influence light utilization and N distribution in the canopy. Field experiments were therefore performed to resolve this issue, using factorial combination of N and K. The interaction between N and K had a significant effect on the grain yield, N uptake, and the NUE of grain production (NUEg), and biomass production (NUEb). The application of either N or K alone resulted in lower yields than the combined application of these nutrients. The combined application of N and K increased rice yields by 54.5% in 2018 and by 76.1% in 2019, compared with N0K0. Similarly, N uptake, NUEg, and NUEb were higher when N was supplied with K than with N application alone. The higher grain yields, N uptake rates, and NUEs observed with the combined N and K treatment were attributed to the following: (1) a higher leaf area index that resulted in better light interception; (2) improved the coordination of light and N distribution within the canopy. Evidence for improved light use by photosynthesis is provided by the observed lower light extinction coefficient (K-L), the higher specific leaf N in the top leaves (SLNo), higher extinction coefficients for effective leaf N (K-N) and K-N/K-L values. We conclude that the interactions between N and K support higher yields by improving canopy performance even at lower N rates.