Synergizing root growth and carboxylate release enhance seed yield in maize-soybean intercropping on acidic karst soils

Context: Southwest China is one of the largest karst regions, where nitrogen (N) deficiency and poor management limit crop productivity. Maize-soybean intercropping is a widely adopted planting model used by farmers across China. Therefore, innovative crop management practices to improve productivity in this region are essential to ensure China's food security. Objective and methods: Ridge-furrow with film mulching (RFM) combined with N supply was introduced for the first time into the maize-soybean intercropping system. Eight treatment combinations (maize and soybean monocultures (M), maize-soybean intercropping with RFM and with ridge-furrow (RF) under 0 (N0) and 150 (N150) kg N ha⁻¹ supply) were used to investigate changes in seed yield, land use efficiency, biomass, N uptake, and root morphological and physiological traits from 2020 to 2023 in Southwest China. Results: The results showed that introduction of RFM into the maize-soybean intercropping system significantly increased maize (13 %) and soybean (42 %) seed yields and land equivalent ratio (LER) (25 %) compared to ridge-furrow without film mulching. Meanwhile, N150 significantly increased maize (33 %) and soybean (24 %) seed yields compared to N0 across four years. The high LER was attributed to the increased yields of maize and soybean, which were associated with higher biomass and N uptake under RFM. The promotion of root growth, such as increased root length and carboxylate release with RFM, enhanced N uptake in both maize and soybean was observed across three years (2021–2023). In addition, N application significantly increased biomass accumulation, N uptake, root length, and carboxylate release at two developmental stages across two years (2022 and 2023), thus contributing to higher seed yields in maize and soybean. Conclusion: RFM combined with N supply can further increase crop yield and land use efficiency in maize-soybean intercropping systems in karst areas. This improvement is explained by the enhancement of the “N-capture”, related to root morphological traits, and “N-mining”, related to carboxylate release, which together increase N uptake, biomass, and ultimately seed yield. Implications: RFM combined with N addition could be considered an efficiency strategy to increase crop productivity in maize-soybean intercropping systems in karst agroecosystems. Our results provided insights into the effects of crop management practices and N addition on N-acquisition strategies and their roles in nutrition uptake and yield formation.