Optimizing nitrogen application and planting density improves yield and resource use efficiency via regulating canopy light and nitrogen distribution in rice

Abstract

Coordinating light and nitrogen (N) distribution within a canopy is crucial to improve rice yield and resource use efficiency. However, little attention has been paid to light and N distribution in response to planting density and N rate, and its relationships with grain yield, radiation use efficiency (RUE), and N use efficiency for grain production (NUEg) in rice. Here, a two-year field experiment was conducted with two hybrid varieties under three N levels, 0 (N1), 90 (N2) and 180 kg ha−1 (N3), and two planting densities, 22.2 (D1) and 33.3 hills m−2 (D2). On average, a 3.4% higher yield and 4.4% higher NUEg were observed under N2D2 compared with N3D1. The extinction coefficient for N (KN) and light (KL) and their ratio (KN/KL) at the heading stage were significantly affected by the N rate, planting density, and their interaction. KN decreased with the increase of N input or planting density. Compared with N1, KN decreased by 43.5 and 58.8% under N2 and N3, respectively, and KN under D2 decreased by 16.0% compared with D1. Higher KL and KN/KL values were observed under a low N rate, while the opposite trend was shown under a high N rate. Moreover, increasing planting density resulted in a decrease in KL and KN/KL values. Compared with N3D1, N2D2 had higher KL and KN, and thus comparable KN/KL. Correlation analysis further revealed that KL was negatively correlated with RUE, while KN and KN/KL were positively correlated with NUEg. Therefore, increasing planting density under reduced N input could ensure rice yield while improving resource use efficiency via regulating canopy light and N distribution.