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

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.