Optimizing planting density to improve nitrogen use of super high‐yield maize

High grain yield and N use efficiency are key goals of crop production. Increasing planting density and supplying adequate N application are important agronomic practices to increase maize grain yield. However, little is known about the interaction between the planting density and N application rate of high‐yield maize under mulch drip irrigation. The objectives of this study were to determine the impacts of planting density and N application rate on the grain yield, economic return, nitrogen partial factor productivity (PFPN), and nitrogen agronomic efficiency (AEN) of super high‐yield maize under mulch drip irrigation in Northwest China. To achieve this, field experiments were conducted in 2017 and 2018 in Qitai farm, Xinjiang. The experiments included four N application levels−no nitrogen (N0), and 270 (N1), 360 (N2), and 450 kg N ha−1 (N3)−and five planting densities−7.5 (D1), 9.0 (D2), 10.5 (D3), 12.0 (D4), and 13.5 plants m−2 (D5). It was found that the N2D4 treatment obtained the highest grain yield (21.5−21.6 t ha−1) and economic return (US$3,399.7−$3,440.3 ha−1) and the relative higher PFPN (59.7−60.1 kg kg−1) and AEN (23.7−25.1 kg kg−1). The PFPN and AEN declined with increasing N application and varied according to a quadratic relationship with increasing planting density. Therefore, a reasonable increase of planting density and an appropriate reduction of N application combined with integrated irrigation−fertilization technology under mulch drip irrigation cannot only obtain high maize yield and economic return but can also improve the N utilization efficiency.