Effects of regulated deficit irrigation on light energy radiation use efficiency of maize-soybean intercropping system

【Objective】Maize-soybean intercropping is a common cultivation technique in Northwestern China. However, one challenge with this system is the uneven distribution of interspecific light energy and the inefficient use of light and irrigation water. This study proposes a strategy to enhance crop canopy cover and photosynthesis by controlling irrigation during the non-critical reproductive period of maize. The objective is to reduce the shading effect of maize on soybean while improving yield and light energy utilization efficiency.【Method】A field experiment was conducted with four irrigation treatments: ① sufficient irrigation for both maize and soybean (IW1), ②sufficient irrigation for maize and deficient irrigation (50%) for soybean (IW2), ③ deficit irrigation for maize (50%) and sufficient irrigation for soybean (IW3), and ④ deficit irrigation (50%) for both maize and soybean (IW4). Soybean was intercropped with two maize varieties: Xianyu 335 (C1) and Longdan (C2). A monocropping system served as the control, with two irrigation treatments: sufficient irrigation (MW1) and deficit irrigation (MW4). The experiment measured morphological indices, net photosynthetic rate (Pn), canopy changes, light energy interception, competition ratio (CR), land equivalent ratio (LER), and irrigation water use efficiency (iWUE) for both crops under each treatment.【Result】① Under the same irrigation treatment, soybean intercropped with C1 showed significantly higher Pn (26.90%), leaf area index (LAI) (5.38%), and aboveground biomass (5.42%) compared to intercropping with C2. Additionally, it reduced the intercepted photosynthetically active radiation (IPAR) of soybean by 6.25% while significantly improving the total radiation use efficiency (RUE) of the intercropping system. ② Changes in irrigation had significant effects on Pn, plant height, LAI, and aboveground biomass for both crops. In particular, IW3 reduced irrigation requirements by 16.79% compared to IW2, significantly increased Pn, LAI, and biomass of soybean, and decreased IPAR by 10.43%. Intercropping improved total RUE by 2.42%. ③ Under the same irrigation treatment, soybean intercropped with C1 had higher yield, iWUE, and CR compared to intercropping with C2. The total LER of C1 also increased by 2.38%. ④ Compared to IW2, IW3 increased soybean yield by 19.95%, total iWUE by 15.17%, and total LER by 8.12%.【Conclusion】Among all treatments, IW3 combined with soybean intercropped with the maize variety Xianyu 335 significantly enhanced soybean growth and improved radiation use efficiency for both crops. This strategy offers a promising approach to optimizing resource use and increasing the productivity of the maize-soybean intercropping system.