Maize–green manure intercropping improves maize yield and P uptake by shaping the responses of roots and soil

Green manuring is essential for improving soil quality and nutrient uptake. With the gradual depletion of phosphorus (P) resources, more attention is being paid to the role of green manures in cultivation systems, such as maize–green manure intercropping, to find possible pathways for enhancing soil P utilization. A maize–green manure intercropping experiment was started in 2009 to investigate the effects and mechanisms for enhancing P uptake and yield in maize. Three species of green manures (hairy vetch (HV), needle leaf pea (NP), sweet pea (SP)) and a sole maize treatment (CK) were used, resulting in four treatments (CK, HVT, NPT, and SPT) in the experiment. During 2020–2023, the intercropping treatments enhanced maize yields in 2020 and 2021, particularly in HVT with increases of 13.7% (1.96 t ha–1) and 13.0% (2.13 t ha–1) compared with CK, respectively. Grain P accumulation of maize was significantly higher in the intercropping treatments than CK in 2020, 2021, and 2023, and with an average increase of 10.6% over the four years (5.2% for NPT, 10.8% for SPT and 15.9% for HVT) compared with CK. Intercropping promoted maize growth with a greater root length density and a higher organic acid release rate. HVT changed the soil properties more dramatically than the other treatments, with increases in the acid phosphatase and alkaline phosphatase activities of 29.8 and 38.5%, respectively, in the topsoil (0–15 cm), while the soil pH was reduced by 0.37 units compared to CK (pH=8.44). Intercropping treatments facilitated the conversion of non-labile P to mod-labile P and stimulated the growth of soil bacteria in the topsoil. Compared with CK, the relative abundance of Gemmatimonadota, known for accumulating polyphosphate, and Actinobacteriota, a prominent source of bioactive compounds, increased significantly in the intercropping treatments, especially in HVT and SPT. A PLS-PM analysis showed that intercropping promoted soil P mobilization and the enrichment of beneficial bacteria by regulating maize root morphology and physiology. Our results highlight that maize–green manure intercropping optimizes root traits, soil properties and bacterial composition, which contribute to greater maize P uptake and yield, providing an effective strategy for sustainable crop production.