Ridge-furrow with black-film mulching enhances phosphorus transformation in rhizosheath soil and grain yield in maize-soybean intercropping systems

Ridge-furrow with film mulching (RFM) increases grain yield by enhancing nutrient uptake and biomass accumulation in monoculture systems. However, its effects on transformation of phosphorus (P) concentration in rhizosheath soil and its role in yield enhancement in maize–soybean intercropping systems under acidic soil conditions, where low P availability in soil limits productivity, remain unclear. A 4-year field experiment with four different treatments was conducted to investigate the effects of film mulching on grain yield, root traits, P concentrations in rhizosheath soil, P-solubilising microorganisms (PSMs) and P-cycling functional genes in a maize–soybean intercropping system. The four treatments given were as follows: ridge-furrow without film mulching at 0-kg P ha⁻¹ (CK), ridge-furrow without film mulching at 90-kg P ha⁻¹ (P90), RFM at 0-kg P ha⁻¹ (FM) and RFM at 90-kg P ha⁻¹ (P90 + FM). The results showed that FM considerably enhanced seed yield, P uptake, root length, concentration of plant-available P in rhizosheath soils, acid phosphatase activity and Al-bound P in maize and soybean. FM remarkably reduced the diversity of maize rhizosheath PSMs, as indicated by a lower Shannon index. Permutational multivariate analysis revealed that FM notably altered the composition of rhizosheath PSMs in both the crops. Furthermore, FM notably increased the abundance of functional genes responsible for organic-P mineralisation, inorganic-P solubilisation, P-starvation response regulation and P transport in rhizosheath soils of maize and soybean. Structural equation modelling demonstrated that FM enhanced P transformation in rhizosheath soils, leading to increased concentrations of plant-available P, improved root morphology and better P uptake—ultimately contributing to higher maize and soybean grain yields in the maize–soybean intercropping system. In conclusion, RFM considerably improved maize and soybean productivity in acidic soils by promoting P transformation, stimulating root growth and increasing rhizosheath PSM abundance as well as increased expression of their P-cycling functional genes. These findings highlight RFM as a sustainable cultivation practice for achieving high grain yield and P-acquisition efficiency by enhancing plant–microbe interactions in maize–soybean intercropping systems.