Phosphorus can effectively reduce selenium adsorption in selenium-rich lateritic red soil.

Phosphorus (P) application can improve the availability of selenium (Se) in soil, which benefits the output of Se-rich agricultural products. However, the mechanism by which P affects the adsorption of Se in Se-rich soil is still unclear. Therefore, this study took Se-rich lateritic red soil as the research object and studied the adsorption behavior of P and Se in the soil through batch adsorption tests and soil characterization technology. The results showed that the adsorption of P or Se in lateritic red soil increased with an increase in equilibrium concentration. The P or Se adsorption process was explained using the Langmuir and Freundlich isotherm models. After adding P, the adsorption of Se decreased from 276-423 mg/kg to 52-201 mg/kg at different initial Se concentrations. The scanning electron microscope and energy dispersive spectrometry (SEM-EDS) results showed that the lateritic red soil was rich in C, O, Fe, Al, and other elements, and the free oxidation states of these elements could efficiently facilitate the adsorption of P and Se. Fourier infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses indicated that both Se and P could react with ferrite groups in the soil to form iron-containing complexes, and there was a competitive adsorption phenomenon, which was the main reason for the decrease in Se adsorption. This study provides theoretical support for further exploring the effect of P on Se behavior in the geochemical cycle. Furthermore, it promotes the efficient use of Se-rich soil resources.