Abstract
Water-saving irrigation, while improving water use efficiency in paddy fields, poses new challenges to the migration and transformation of soil phosphorus, whereas the mechanism of biochar—a key soil amendment—in phosphorus cycling of paddy soils remains unclear. In this study, a water-saving irrigated paddy field was used as the research object, and different biochar application rates were set to systematically evaluate the responses of available phosphorus (AP), total phosphorus (TP), phosphorus activation coefficient (PAC), and adsorption–desorption characteristics through field experiments and laboratory analyses, with Langmuir and Freundlich isotherm models applied for fitting. The results showed that an appropriate biochar application promoted the increase of AP and PAC in surface soils while reducing TP content, thereby significantly improving phosphorus activation. Meanwhile, biochar altered the interfacial reaction characteristics of soil phosphorus, manifested as a dynamic regulatory effect on adsorption capacity and desorption potential, with more pronounced trends observed under higher application rates. The findings suggest that biochar optimises the pathways of phosphorus migration and transformation and regulates interfacial reactions in paddy soils under water-saving irrigation, thus enhancing phosphorus bioavailability and utilisation efficiency. This study provides a scientific basis and technical support for the efficient use and sustainable management of phosphorus resources in water-saving irrigated paddy fields.
