Optimizing Planting Density to Increase Maize Yield and Water Use Efficiency and Economic Return in the Arid Region of Northwest China

High grain yield and water use efficiency (WUE) are the key goals when producing maize (Zea mays L.) under irrigation in arid areas. Increasing the planting density and optimizing irrigation are important agronomic practices for increasing the maize grain yield and WUE. A two-year field experiment was conducted to investigate the effects of planting density and irrigation on the maize grain yield, WUE, and economic return of spring maize under a mulch drip irrigation system in Xinjiang, Northwest China. The experiment included four irrigation levels and five planting densities. The results showed that the reduction of irrigation decreased the yield and evapotranspiration (ETc) but improved the WUE. Increasing the planting density increased the ETc, but there was a quadratic curve relationship between yield and WUE and planting density. Treatment with 600 mm of water and 12 plants m(-2) obtained the highest grain yield (21.0-21.2 t ha(-1)) and economic return (3036.0 USD ha(-1)) and a relatively high WUE (2.64-2.70 kg kg(-1)). Therefore, a reasonable increase in planting density and an appropriate reduction of irrigation combined with drip irrigation under a mulch system can simultaneously achieve high yields and economic return and high WUE in maize production.