In‒situ immobilization remediation, soil aggregate distribution, and microbial community composition in weakly alkaline Cd‒contaminated soils: A field study

Abstract

Biochar has advantages of a large specific surface area and micropore structure, which is beneficial for immobilization remediation of heavy metal‒contaminated soils. A field experiment was conducted to investigate the effects of rice husk biochar (BC) (7.5, 15, and 15 t hm−2) on Cd availability in soils and accumulation in maize (Zea mays L), soil aggregate structure, and microbial community abundance. The results show that BC treatment promoted the formation of large aggregates (5–8 and 2–5 mm) and enhanced aggregate stability, whereas it decreased the proportion of ≤0.25 mm soil aggregates. The geometric mean diameter and mean weight diameter under BC‒treated soils increased by 9.9%–40.5% and 3.6%–32.7%, respectively, indicating that the stability of soil aggregates increased. Moreover, BC facilitated the migration of Cd from large particles (>0.5 mm aggregates) to small particles (<0.25 mm aggregates). The application of BC decreased diethylenetriamine pentaacetic acid ‒extractable Cd by 17.6%–32.12% in contrast with the control. The amount of Cd in maize was reduced by 56.7%–81.1% for zhengdan958, 52.4%–85.9% for Sanbei218, and 73.7%–90.4% for Liyu16. When compared with the control groups, BC addition significantly (P < 0.05) increased the number of Ace observed, Shannon diversity indices, and the relative abundances of Proteobacteria, Acidobacteria, and Bacteroidetes. Therefore, rice husk BC exhibited a certain feasibility in immobilizing remediation of weakly alkaline Cd‒contaminated soils.