Low light is a major adversity affecting yield and quality of summer maize in the Huang‐Huai‐Hai region of China. We conducted a field experiment to explore the effects of shading on root development and yield formation in two summer maize hybrids (Zea mays L.), Denghai605 (DH605) and Zhengdan958 (ZD958). The experiment consisted of four treatments (CK: ambient sunlight, S1: shading from tasselling to physiological maturity stage, S2: shading from six‐leaf to tasselling stage, S3: shading from seeding to physiological maturity stage). Shading had a strong impact on the development of roots in the upper soil layer. Shading significantly decreased the root dry weight, root/shoot ratio, root length density, root absorption area and active absorption area. The results showed that treatments in a diminishing sequence of effects on root from S3, S1, S2 to CK. Overall, shading decreased the root morphologic and activity indices, and decreased yield in summer maize. During an average of 2 years, yields of ZD958 in S3, S2 and S1 decreased by 85%, 24% and 55%, yields of DH605 in S3, S2 and S1 decreased by 87%, 26% and 67%, in compare to CK. The results will be useful for hybrid selection and improving cultural practices for enhancing the maize shading resistance in Huang‐Huai‐Hai region.

SUMMARYUnderstanding the physiological mechanisms of biomass accumulation and partitioning in the grain, and the nitrogen (N) uptake associated with different plant densities and N management strategies, is essential for achieving both high yield and N use efficiency (NUE) in maize plants. A field experiment was conducted in 2013 and 2014, using five rates of N application and three plant densities (6·0, 7·5 and 9·0 plants/m2) in Quzhou County on the North China Plain (NCP). The objective was to evaluate whether higher plant density can produce more biomass allocated to the grain to achieve higher grain yield and to determine the optimal N management strategies for different plant densities. The highest grain yield and NUE were achieved in the 7·5 plants/m2 treatment; both the sub-optimal (6·0 plants/m2) and supra-optimal (9·0 plants/m2) plant densities resulted in diminished yield and NUE. Compared to 6·0 plants/m2, the 7·5 plants/m2 treatment displayed higher biomass accumulation during the grain-filling period and also exhibited more biomass allocated to kernels with similar total biomass accumulation compared with the 9·0 plants/m2 treatment, which contributed to its higher grain yield. The N uptake in the 7·5 plants/m2 treatment was similar to that in the 9·0 plants/m2 treatment up to pre-silking. However, the post-silking N uptake of the 7·5 plants/m2 treatment was 66·4 kg/ha, which was 29·1% higher than that of the 9·0 plants/m2 treatment. Furthermore, the highest maize grain yield was achieved in the 0·7 × optimal N rate (ONR × 0·7), ONR and ONR × 1·3 treatments for 6·0, 7·5 and 9·0 plants/m2, respectively, which suggests that different N management strategies are needed for different plant densities. In conclusion, selecting a planting density of 7·5 plants/m2 with an in-season root zone N management is a potentially effective strategy for achieving high grain yield and high NUE for maize production on the NCP.

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