Increasing Planting Density and Optimizing Irrigation to Improve Maize Yield and Water-Use Efficiency in Northeast China

We investigated the effects of variety, planting density, and irrigation amount on grain yield, water-use efficiency (WUE), and evapotranspiration (ETc). The trial was conducted in Tong Liao, Inner Mongolia, from 2021 to 2022, with compact variety Dika159 (DK159) and conventional variety Zhengdan958 (ZD958) as the test materials. The planting density was set to 6.0 × 104 plants/ha (D1, local farmer planting density) and 9.0 × 104 plants/ha (D2), with five irrigation levels: 450 mm (W450, irrigation amount used by local farmers, CK); 360 mm (W360); 270 mm (W270); 180 mm (W180); and 90 mm (W90). The results indicate that the yield and WUE of variety DK159 increased by 7.48% and 5.00%, compared to ZD958, respectively. Increasing planting density enhanced yield by 13.32–15.57% in maize yield and 9.55–11.47% in WUE. Maize yield exhibited a trend of increasing linearly with the irrigation amount before reaching a plateau, reaching a maximum (16.62–17.39 t/ha) and high WUE (2.45–2.49 kg/m3) with DK159-D2-W270. The highest water consumption intensity occurred during the silking stage to the milk stage for different densities and varieties. The results indicate that selecting compact varieties, increasing planting density, and optimizing irrigation amount through integrated drip irrigation and water fertilizer can effectively improve maize yield and WUE.