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We hypothesized that soil phosphorus (P) utilization might be tightly associated with interspecific interactions. To clarify this issue, a maize-grass pea intercropping system was investigated in a rainfed field with P addition (P0 and P +), water (rain-fed and plastic film mulching) and isolation (root barrier and root intermingling) treatments. The data indicated that total net effect was higher than 0 under all the conditions, displaying facilitative effects of biodiversity on agroecosystem productivity. The dynamics of total land equivalent ratio demonstrated that the intensity of plant-plant facilitation became greater under P-deficient condition. Maize was the facilitated species consistently, while grass pea changed from facilitated species under low soil P and moisture to facilitator under high soil P and moisture. The driving mechanism was associated with soil acidification and microbial community promotion effect under P-deficient condition. Intercropped rhizosphere soil phosphatase activity was increased by 4.9–17.2%, and Olsen-P availability was evidently enhanced relative to monoculture. Interestingly, drought stress significantly enhanced this trend. Critically, root isolation confirmed that plant-plant facilitation was briefly driven by interspecific rhizosphere interactions. Conclusively, this study confirmed the context-dependent facilitation shift in agroecosystem and provided a novel insight into the importance of rhizosphere interaction on soil P availability and utilization. [Display omitted] • Plant-plant facilitation was observed in the maize-grass pea intercropping system. • The intensity of facilitation decreased from low to high P and water gradients. • P deficiency promotes rhizosphere phosphatase activity and acidification process. • Drought and P deficiency led to the optimal soil microbial biomass and activities. • Intercropped grass pea fostered soil P mineralization and resource use efficiency. [ABSTRACT FROM AUTHOR]