Phosphorus availability-leaching trade-offs under long-term organic substitution: Synergistic microbial activation and adsorption capacity decline

Partial substitution of chemical fertilizers with manure enhances soil phosphorus (P) availability; yet, the trade-off between P supply and leaching risks under varying substitution rates remains unclear, particularly with regard to microbial-driven P transformation and soil P retention capacity. Here, we combined ³¹P NMR, sequential extraction, and microbiology techniques in a 15-years field experiment with an in-situ lysimeter to investigate P dynamics. Five treatments were applied: no N input (NoN), only chemical NPK (CN), and manure substitution for chemical N at 25 % (CNM1), 50 % (CNM2), and 75 % (CNM3), with equal NPK amounts. Compared to CN, manure substitution significantly increased the vegetable yield and P uptake, 15-year average yields of tomato and celery increased by 6.7 %–12.7 % and 10.5 %–15.4 %. Compared with NoN and CN, manure substitution increased the contents of soil labile and moderately labile P, orthophosphate monoesters and diesters, microbial biomass C and P, and alkaline phosphatase activity in both the tomato and celery seasons. CNM3 increased soil phoD and Bradyrhizobium abundance, sharply decreased P adsorption capacity, and increased total P leaching by 20.5 %–23.7 %, while CNM2 resulted in higher complexity and connectivity of phoD-harboring microbial networks and significantly decreased P leaching by 6.3 %–30 %. Manure substitution enhanced labile P by decreasing soil pH, promoting organic C accumulation, and upregulating the phoD gene. High manure substitution exacerbated P leaching predominantly by reducing P adsorption capacity and stimulating microbial mineralization of organic P. These findings provide new insights into understanding the roles of organic substitute strategies in soil P dynamics, and moderate amount substitution (≤50 %) enhances P availability while mitigating leaching, providing a critical strategy for sustainable P management.