Water-saving strategies in intercropping systems: Integrated effects of water regulation and planting patterns on root-canopy coordination and agricultural water productivity

Water scarcity and soil degradation are critical challenges confronting agricultural production in arid and semi-arid regions. Wolfberry is a key industrial crop in arid regions, contributing significantly to local specialty agriculture. Enhancing its growth environment and optimizing water utilization are essential for the sustainable use of agricultural resources and the advancement of modern agroforestry production systems. This study investigated the effects of water regulation and planting patterns on a wolfberry-alfalfa system through a three-year field experiment. Four irrigation regimes (full irrigation, W0; mild deficit, W1; moderate deficit, W2; severe deficit, W3) were applied under two planting patterns (monoculture, M; intercropping, I). Key indicators assessed included soil water dynamics, root-canopy characteristics, yield, and water-use efficiency. The results indicated that soil water content (SWC) decreased with horizontal distance and varied with depth, with intercropping systems generally exhibiting lower SWC than monoculture systems (W0 > W1 > W2 > W3), with reductions ranging from 3.09 % to 9.22 %. Root length density (RLD), leaf area index (LAI), cumulative intercepted photosynthetically active radiation (CIPAR), and radiation use efficiency (RUE) were maximized under MW1 and IW0 treatments. However, the yield advantage of intercropped wolfberry was not statistically significant compared to monoculture. Among all treatments, IW1 achieved the highest net income (78,235.20 CNY·ha⁻¹) and the greatest economic water use efficiency (16.23 CNY·m⁻³), exceeding other treatments by 6.38 %-224.49 % and 6.36 %-146.66 %, respectively. Stepwise multiple linear regression analysis identified the fraction of photosynthetically active radiation (FPAR) and RUE as the primary determinants of wolfberry yield. The comprehensive evaluation concluded that mild deficit irrigation (65 %-75 % θ_f) emerged as an effective strategy for improving water productivity in northwestern China and comparable arid environments.