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 (PFP N ), and nitrogen agronomic efficiency (AE N ) 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 PFP N (59.7−60.1 kg kg −1 ) and AE N (23.7−25.1 kg kg −1 ). The PFP N and AE N 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.