Interaction between plant density and nitrogen management strategy in improving maize grain yield and nitrogen use efficiency on the North China Plain

Understanding 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) inmaize 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/m(2)) 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/m(2) treatment; both the sub-optimal (6.0 plants/m(2)) and supra-optimal (9.0 plants/m(2)) plant densities resulted in diminished yield and NUE. Compared to 6.0 plants/m(2), the 7.5 plants/m(2) 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/m(2) treatment, which contributed to its higher grain yield. The N uptake in the 7.5 plants/m(2) treatment was similar to that in the 9.0 plants/m(2) treatment up to pre-silking. However, the post-silking N uptake of the 7.5 plants/m(2) treatment was 66.4 kg/ha, which was 29.1% higher than that of the 9.0 plants/m(2) treatment. Furthermore, the highest maize grain yield was achieved in the 0.7 x optimal N rate (ONR x 0.7), ONR and ONR x 1.3 treatments for 6.0, 7.5 and 9.0 plants/m(2), respectively, which suggests that different N management strategies are needed for different plant densities. In conclusion, selecting a planting density of 7.5 plants/m(2) 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.