Fe-Modified Common Reed Biochar Reduced Cadmium (Cd) Mobility and Enhanced Microbial Activity in a Contaminated Calcareous Soil

Abstract

The immobilization of soil cadmium (Cd) by biochar and modified biochar is an eco-friendly and cost-effective strategy. In the current study, the effect of raw biochar (BC) and iron-modified biochar (Fe-BC) derived from common reed on the fractionation and mobility of Cd was evaluated, as was its effect on soil microbial activity in contaminated calcareous soil. Treatments involved a combination of two factors: type of biochar (CK: Control, BC, and Fe-BC) and soil Cd concentration (0, 15, and 30 mg kg−1). Treatments were applied to the soil and incubated for 90 days. The application of both biochars increased soil pH and soil organic carbon content (16.6–48.0%), microbial biomass carbon (40.5–75.1%), basal respiration (16.6–48.0%), substrate-induced respiration (12.4–41.9), and dehydrogenase activity (25.5–102.1%), while it reduced diethylene-triamine pentaacetic acid (DTPA)-extractable Cd (22.1–39.5%). The addition biochars, particularly Fe-BC, prominently decreased the concentration of exchangeable and carbonate fractions and increased the concentration of Fe-MnOx, as well as the organic and residual fractions of Cd in the soil. Moreover, relative to the control treatment, the incorporation of raw and Fe-modified biochar into 30 mg kg−1 Cd-spiked soil significantly decreased the Cd mobility factor (MF) value by 14.5 and 21.8%, respectively. Fe-modified biochar had a more significant impact than raw biochar on the immobilization of Cd in the soil, and its improved soil microbial activity to a greater extent. Overall, the findings indicate that Fe-modified biochar derived from common reed can immobilize Cd and improve soil microbial attributes in contaminated calcareous soil. Therefore, it can be used as an eco-friendly amendment for restoring Cd-contaminated calcareous soil.