The fate of fertilizer-derived phosphorus under different long-term fertilization regimes: A phosphate oxygen isotope...

Understanding the fate of exogenous fertilizer-derived inorganic phosphorus (P_i) is essential for effective P management. Hence, this study carried out a 180-day incubation experiment with or without KH₂P¹⁸O₄ in soils with four different fertilization regimes [without fertilizer (CK), mineral P and K fertilizer (PK), mineral N, P, and K fertilizer (NPK), compost (OM)]. We analyzed the atom % excess in phosphate oxygen isotope of sequentially extracted P_i pools (H₂O-P_i, NaHCO₃-P_i, NaOH-P_i, and HCl-P_i), soil respiration, potential phosphatase activities, and microbial biomass. Our results showed that exogenous phosphate fertilizer was immediately transformed into the H₂O-P_i and NaHCO₃-P_i pools and gradually partially immobilized in the HCl-P_i pool. Additionally, biotransformation plays an important role in the turnover of fertilizer-derived P_i. After the 180-day incubation, the biologically transformed H₂O-P_i content was significantly (P<0.05) reduced by 63.2 % on average, with the largest reduction in PK. The NaHCO₃-P_i gradually increased in both CK and OM through biotic processes. However, it continuously decreased in PK and NPK, likely due to the strong adsorption and microbial fixation. The NaOH-P_i fluctuated slightly in CK, NPK, and OM while gradually decreasing in PK. At the end of the incubation, 28.6 %, 37.0 %, 61.2 %, and 75.2 % of the P_i increment in CK, OM, NPK, and PK were stored in the HCl-P_i pool, respectively. Overall, these findings provide important information on the dynamics of fertilizer-derived P_i, delivering new insights into rational phosphate fertilizer management and sustainable agricultural development.