Irrigation and Planting Density Effects on Apple–Peanut Intercropping System

The western Shanxi Loess region, as a typical semi-arid ecologically fragile zone, faces severe soil and water resource constraints. The apple–peanut intercropping system can significantly improve water productivity and economic benefits through complementary resource utilization, representing an effective approach for sustainable agricultural development in the region. This study took the apple–peanut intercropping system as the research object (apple variety: ‘Yanfu 8’; peanut variety: ‘Huayu 38’), setting three peanut planting densities (D1: 27,500 plants/ha; D2: 18,333 plants/ha; D3: 10,833 plants/ha) and two water regulation measures—W1 (irrigation upper limit at 85% of field capacity, FC) and W2 (65% FC), with non-irrigated controls (CK) at different planting densities for comparison. This study systematically analyzed the synergistic regulation effects of intercropping density and water management on system water use and comprehensive benefits. Results showed that medium planting density combined with medium irrigation (W2D2 treatment) could maximize intercropping advantages, effectively improving the intercropping system’s soil water content (SWC), yield (GY), and water use efficiency (WUE). This research provides a theoretical basis for precision irrigation in fruit–crop intercropping systems in semi-arid regions. However, based on the significant water-saving and yield-increasing effects observed in the current experimental year, follow-up studies should verify its stability through multi-year fixed-position observation data.