Rice Canopy Light Resources Allocation, Leaf Net Photosynthetic Rate, and Yield Formation Characteristics Response to Combined Application of Nitrogen and Potassium

Fertilizers play vital roles in agricultural production, especially for nitrogen (N) and potassium (K). The plant canopy is the main site for photosynthesis and a key factor affecting rice yield formation. The present field studies were aimed at investigating the interactive effects of N (0, 90, and 180 kg N ha −1 ) and K (0, 60, and 120 kg K 2 O ha −1 ) on canopy architecture, radiation interception, leaf photosynthesis, dry matter accumulation, and radiation use efficiency of japonica rice. In comparison with the control (N0K0; 0 kg N and 0 kg K 2 O ha −1 ) treatment, the combined use of N and K significantly increased the leaf area index (LAI), the intercepted photosynthetically active radiation (IPAR), the dry matter accumulation, and the photosynthetically active radiation use efficiency (PARUE) by 105.8 and 106.1%, 45.1 and 33.0%, 142.0 and 121.9%, and 66.8 and 66.9% at full heading stage, in 2020 and 2021, respectively. Likewise, the combined use of N and K also significantly increased the leaf photosynthesis (P n ) and the grain yield by 17.3 and 23.0% and 113.8 and 105.9%, compared with that of the N0K0 treatment. N and K interactive effects on IPAR, P n and grain yield, and N180K120 treatment was the most reasonable treatment. This word elicit that the combined use of N and K significantly promoted the development of rice leaf, enhanced the radiation interception and use efficiency, and ultimately increased the dry matter accumulation and grain yield.