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

Abstract

Understanding the fate of exogenous fertilizer-derived inorganic phosphorus (Pi) 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 Pi pools (H2O-Pi, NaHCO3-Pi, NaOH-Pi, and HCl-Pi), soil respiration, potential phosphatase activities, and microbial biomass. Our results showed that exogenous phosphate fertilizer was immediately transformed into the H2O-Pi and NaHCO3-Pi pools and gradually partially immobilized in the HCl-Pi pool. Additionally, biotransformation plays an important role in the turnover of fertilizer-derived Pi. After the 180-day incubation, the biologically transformed H2O-Pi content was significantly (P<0.05) reduced by 63.2 % on average, with the largest reduction in PK. The NaHCO3-Pi 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-Pi 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 Pi increment in CK, OM, NPK, and PK were stored in the HCl-Pi pool, respectively. Overall, these findings provide important information on the dynamics of fertilizer-derived Pi, delivering new insights into rational phosphate fertilizer management and sustainable agricultural development.