High-efficiency immobilization of soil available cadmium by chicken manure and its derivatives: Roles of chemical and microbial property

To quantify the roles of chemical and microbial effects to cadmium immobilization by chicken manure (CM), chicken manure ash (A-CM), and chicken manure biochar (CMB), the dynamic changes in metal speciation, soil chemical properties , enzyme activities , and microbial community diversity were examined. The extractable metal contents in soil were decreased by 9.12 %, 31.26 %, and 43.87 % under the treatment of CM, A-CM, and CMB, respectively. Soil pH, cation exchange capacity (CEC), available phosphorus (AP), available potassium (AK), dehydrogenase (DHA), and catalase (CA) activities were increased by the three treatments, in which CEC and AP (chemical effect) as well as DHA and CA (microbial effect) showed negative correlations with extractable metal. The diversity and association of microbial communities were inhibited by CM and A-CM, while no significant changes were observed by CMB. Bacterial communities exhibited greater sensitivity to soil properties than fungal communities under the three treatments, in which Gemmatimonadota , Proteobacteria , and Bacteroidota displayed significant negative correlations with extractable metal. Microbial effects could contribute 48.26 %, 46.56 %, and 30.52 % to the decrease of extractable metal under the treatment of CM, A-CM, and CMB, while the chemical effects account for 51.74 %, 53.44 %, and 69.48 %, respectively. This suggested microbial property was less important in the metal immobilization than that of chemical property, as also supported by the partial least squares path model (PLS-PM) and variance partitioning analysis (VPA). These would deepen understanding of the relative contribution of mechanisms to heavy metal immobilization in soils , which is important for the improvement of biochars in environmental mediation. • Chicken manure and its derivatives significantly decreased the available Cd, particularly in the CMB treatment. • Chicken manure and its derivatives improved soil properties, especially in pH and CEC. • Chicken manure and its derivatives significantly altered soil microbial community structure and diversity. • Chemical properties dominated Cd immobilization, contributing 58.22 %, whereas microorganisms accounted for 41.78 %.