Influence of chloride, sulphate, phosphate, and silicate-based potassium fertilizers and rice husk biochar on cadmium fate, complexation, leaching and uptake in maize under alkaline soil conditions.

Cadmium (Cd) behavior in alkaline soils is primarily controlled by the interplay of solution complexation, anion- mediated transformation, and solid-phase interactions. The experiment included a series of integrated analyses to monitor Cd speciation, mobility, transformation, leaching, and fate in maize plants. Soil solution chemistry, bioavailability, and leachate-mediated Cd release kinetics were monitored alongside maize growth, yield, and Cd accumulation patterns, as well as associated health risks. In the present work, we examined Cd fate under five potassium-sourced (@200 mg kg-1 K) fertilizers (K-0-Control, KCl, K2SO4, K2HPO4, K2SiO3) with and without 1% rice husk biochar (RHB) for the maize crop. The chloride (Cl-) promoted formation of highly soluble Cd complexes promoting Cd displacement and leaching, in comparison sulphate (SO42-) resulted in less mobile fraction of Cd compared to control with no K. Potassium related phosphate (HPO42-) and silicate (SiO32-) anions resulted in substantial decrease in bioavailable fractions as well as leaching of Cd from soil, along with decreased maize root, shoot and grain accumulations, coupled with higher maize yield, improved physiology, biochemical performances and crop health. The improved maize crop parameters with potassium-sourced nutrition suggest a role for potassium nutrition in the net reversal of Cd toxicity, mutually driven by HPO42- and SiO3- anions. The inclusion of RHB resulted in a substantial reduction in Cl- mediated Cd mobility, along with further enhancing HPO42- and SiO32- mediated Cd immobilization in soil, along with better plant growth and yield, proving it a better supplementary soil amendment.