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

Light and nitrogen distribution within a plant's canopy reflect growth adaptation of crop to the environment and are conducive to improving the carbon assimilation ability. So is it possible to rationalize regulation in crop production to maximize yield by improving light and nitrogen distribution without adding additional inputs? In this study, the effects of different nitrogen application rates and planting densities on canopy light and nitrogen distribution of two high-yielding maize cultivars (i.e., XY335 and DH618) and the regulation of canopy physiological characteristics on radiation use efficiency (RUE) and yield were studied based on high yield field experiments in Qitai, China, during 2019 and 2020. The results showed that the distribution of photosynthetically active photon flux density (PPFD) in the maize canopy has been decreasing 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 of XY335 and DH618 were 0.5 and 0.3, corresponding to 40.6 and 49.3% of the total leaf area index (LAI). The KN/KL in the middle and lower canopy of the XY335 (0.32) was 0.08 higher than that of DH618 (0.24). Yield and RUE of the XY335 (17.2 t ha-1, 1.8 g MJ-1) were 7.0% (1.1 t ha-1) and 13.7% (0.2 g MJ-1) higher than that of DH618 (16.1 t ha-1, 1.6 g MJ-1). Therefore, better light conditions (the proportion of LAI in the upper and middle canopy is small) improved the light distribution when SLN started to decrease, thus helping to mobilize nitrogen distribution and maintain a high nitrogen extinction coefficient (KN) and KN/light extinction coefficient (KL). And KN/KL was a key parameter for yield improvement when maize nutrient requirements were met at 360 kg ha-1. At this time, an appropriately optimized high planting density could promote nitrogen utilization and produce higher yield and higher efficiency. This study will be important for maize high yield and high efficiency cultivation and breeding in the future.