Simulation of soil water balance and crop productivity of long-term continuous maize cropping under high planting density in rainfed agroecosystems

Increasing planting density is one of the main management practices contributing to maize grain yield improvements across the world, but the soil water sustainability after long-term continuous high-density under rainfed farming systems is not clear. Crop simulation models may help explore suitable management systems for increasing crop productivity and economic benefits. The present study calibrated and validated the DSSAT-CERES-Maize model in a four-year field experiment, which coupled four densities from 52,500 to 97,500 plant ha -I- and two cultivars under rainfed conditions. The calibrated CERES-Maize model performed fairly well in simulating the phenological dates, and the average root mean-squared error (RMSE) ranged from 0.7 to 2.8 d for anthesis and 0 to 2.8 d for maturity date. The normalized root mean squared errors (nRMSE) for biomass and grain yield were 17.5% and 12.4%, respectively. The average nRMSE for soil water dynamics in the 0-200 cm soil layers was 15.6% among the different growth stages. The calibrated model was subsequently used to evaluate the soil water regime and crop productivity in response to planting density under 38 years of meteorological data. The results showed that maize water productivity and evapotranspiration (ET) fluctuated with seasonal rainfall, and normal and wet years were significantly higher than dry years. Although ET during the growing season tended to increase with increasing density, the long-term continuous high planting density did not cause excessive soil water consumption. Grain yield and water use efficiency (WUE) tended to exhibit a parabolic relationship with planting density during the long-term simulated seasons between different experimental sites. No significant differences were detected between different cultivars in water productivity under long-term simulation. However, the simulation results suggested that the optimal planting density was often related to variability in climate conditions between sites and years. The scenario simulation results suggest that the optimal density should not exceed 67,500 plant ha(-1) when the annual precipitation is less than 500 mm, but it should not exceed 82,500 plant ha(-1) in areas where the rainfall is greater than 500 mm. Therefore, this study suggests that moderate planting density has the potential to realize sustainable maize development in dryland farming systems on the Loess Plateau and similar areas.