Biochar application as a soil amendment for decreasing cadmium availability in soil and accumulation in Brassica chinensis

Abstract

Purpose Biochar has emerged as a promising material for limiting the bioavailability of potentially toxic elements in contaminated soils. Despite the benefits associated with the agricultural use of biochar, there is minimal information available on biochar amendment of Cd accumulation in leafy vegetable cultivars. Materials and methods A pot experiment was carried out to evaluate the feasibility of bamboo biochar (BB) and rice straw biochar (RSB) for decreasing cadmium (Cd) availability in artificially contaminated (Cd at 50 mg kg⁻¹) soil, and its accumulation in Brassica chinensis. Biochar was applied at 0 (control), 0.5, 1, 2.5, and 5% (w/w). Results and discussion RSB at 5% significantly reduced the availability of Cd in soil (by 19.3%) compared with BB (by 8.6%). Application of BB and RSB at 1–5% markedly enhanced soil pH by 1.17–5.48 and 2.47–7.46%, respectively. Moreover, soil organic carbon was improved by 40.3–155 and 22.2–111% with 1–5% BB and RSB amendment, respectively. Soil total N was significantly increased by 24.5 and 31.1% with 5% BB and RSB application, respectively. Soil available P was increased by 10.8–24.4 and 14.6–30.7% with 2.5–5% BB or RSB amendment, respectively. Application of 2.5–5% BB and RSB significantly increased soil available K by 76.8–291 and 203–627%, respectively. Biochar at 2.5–5% ratio significantly improved nutrient (P and K) uptake in B. chinensis. Furthermore, biochar was more effective at higher rates, and RSB performed better than BB as a soil nutrient supplement. Cd accumulation in B. chinensis was significantly reduced by 12.0–48.3 and 17.0–35.4% with 0.5–5% BB and 1–5% RSB amendment, respectively. Greater biochar application further decreased bioconcentration factor (BCF) in harvested B. chinensis (all values Conclusions Our results suggest that BB and RSB, especially at higher rates (> 2.5%), could be recommended as safe amendments for the immobilization of Cd in contaminated agricultural soils, thereby decreasing its threat to the food chain and human health.