Optimized canopy structure improves maize grain yield and resource use efficiency

Improved canopy structure was instrumental in setting maize yield records, and yet it has rarely been examined in China. At Qitai Farm in Xinjiang, we conducted a 4-year field experiment using China's six highest-yielding maize hybrids sorted into three yield level groups that were grown at similar growth durations and at optimum densities. The average yield of high-yield level (HL, 22.3 Mg ha(-1)) was 7.2% and 24.6% higher than that of medium-yield level (ML) and low-yield level (LL), respectively. For each yield level, we measured morphological traits that influence canopy structure and yield. They included plant height, ear height, ear ratio, internode length, leaf numbers, leaf angle, LOV, leaf area, and spatial density of leaf area. Among the preceding morphological traits of the three yield levels, HL's best optimized the canopy structure, as shown by improved light distribu Lion (19.0% light transmission at the ear) and increased light interception per unit leaf area per day (UFA, 51.7 MJ m(-2) day(-1)) in the canopy. In comparison, light transmission was 12.2% and 15.9% at the ear and the total LIPA5 were 37.2 and 29.0 MJ m(-2) day(-1) at silking for ML and LL, respectively. HL had significantly longer leaf area duration and a higher photosynthetic rate, especially at the grain filling stage, and its total accumulated biomass at maturity was significantly better (by 13.9%) than LL's. HL's harvest index (0.54) was significantly higher than that of ML (0.52) and LL (0.48). HL's radiation and heat use efficiencies were 2.61% and 1.37 g degrees C-1 day(-1) m(-2), both significantly greater than those of ML and LL. Therefore, optimum maize plant types can significantly improve canopy structure and increase resource use efficiency and grain yield.