Fertilization of potentially toxic element-contaminated soils remediated with reusable biochar pellets using rice straw, pig manure and their derived biochar.

Potentially toxic elements (PTEs) are widespread pollutants in agricultural fields, presenting significant challenges to the maintenance of soil ecological functions while simultaneously reducing their concentrations. This study detailed the development of a high-strength reusable silicate magnetic composite biochar sphere (SMBCS) characterized by superior magnetic and adsorption properties, synthesized from natural minerals and biochar. The application of SMBCS over three consecutive remediation cycles led to reductions in cadmium (Cd), lead (Pb), and arsenic (As) concentrations in soil by 28.6%, 26.6%, and 42.9%, respectively, accompanied by corresponding decreases in bioavailability of 52.7%, 49.4%, and 39.4%. The accumulation of Cd, Pb, and As in rice seedlings cultivated in the remediated soil decreased by 79.50-85.47%, 38.05-38.99%, and 39.56-77.10%, respectively. However, the removal of essential mineral nutrients (Al, Fe, K, Ca, Mg, Si, N, Zn, Mn, and Cu) from the soil ranged from 3.26% to 36.28%, which adversely affected seed germination and rice seedling growth. Pre-planting fertilization with rice straw (RS), pig manure (PM), biochar (RSB and PMB), and regenerated SMBCS (RSMBCS1 and RSMBCS2) effectively reduced Cd (0.20-45.40%) and Pb (8.70-35.36%) uptake while enhancing the bioavailability of mineral nutrients, thereby promoting crop growth and physiological traits. The SMBCS-fertilization technique emerges as a viable approach for the removal of PTEs in agricultural soils, facilitating the restoration of ecological functions and ensuring safe agricultural production.