Matching the light and nitrogen distributions in the maize canopy to achieve high yield and high radiation use efficiency

The distributions of light and nitrogen within a plant's canopy reflect the growth adaptation of crops to the environment and are conducive to improving the carbon assimilation ability. So can the yield in crop production be maximized by improving the light and nitrogen distributions without adding any additional inputs? In this study, the effects of different nitrogen application rates and planting densities on the canopy light and nitrogen distributions of two high-yielding maize cultivars (XY335 and DH618) and the regulatory effects of canopy physiological characteristics on radiation use efficiency (RUE) and yield were studied based on high-yield field experiments in Qitai, Xinjiang Uygur Autonomous Region, China, during 2019 and 2020. The results showed that the distribution of photosynthetically active photon flux density (PPFD) in the maize canopy decreased from top to bottom, while the vertical distribution of specific leaf nitrogen (SLN) initially increased and then decreased from top to bottom in the canopy. When SLN began to decrease, the PPDF values of XY335 and DH618 were 0.5 and 0.3, respectively, corresponding to 40.6 and 49.3% of the total leaf area index (LAI). Nitrogen extinction coefficient (K_N)/light extinction coefficient (K_L) ratio in the middle and lower canopy of XY335 (0.32) was 0.08 higher than that of DH618 (0.24). The yield and RUE of XY335 (17.2 t ha^–1 and 1.8 g MJ^–1) were 7.0% (1.1 t ha^–1) and 13.7% (0.2 g MJ^–1) higher than those of DH618 (16.1 t ha^–1 and 1.6 g MJ^–1). Therefore, better light conditions (where the proportion of LAI in the upper and middle canopy was small) improved the light distribution when SLN started to decline, thus helping to mobilize the nitrogen distribution and maintain a high K_N and K_N/K_L ratio. In addition, K_N/K_L was a key parameter for yield improvement when the maize nutrient requirements were met at 360 kg N ha^–1. At this level, an appropriately optimized high planting density could promote nitrogen utilization and produce higher yields and greater efficiency. The results of this study will be important for achieving high maize yields and the high efficiency cultivation and breeding of maize in the future.