Biochar effects acidic soil remediation and Brassica oleracea L. toxicity—A case study in subtropical area of China

As an important part of the terrestrial ecosystem, agriculture ecosystem plays a key role in supporting and maintaining human survival on earth. To restore contaminated sites as well as improve soil fertility, applying biochar to soil is an environmentally approachable technology. To evaluate the benefit of applying peanut shells biochar (PNB) to the soil, a glasshouse experiment was conducted at a ratio of biochar of 2%, 4%, and 6% of either type of biochar. The results indicated that PNB application increased soil pH, electric conductivity (EC), total carbon (TC), total nitrogen (TN), and dissolved organic carbon (DOC) in soil. The bioavailable concentration of PTEs such as cadmium (Cd), nickel (Ni), arsenic (As), chromium (Cr) and lead (Pb) significantly (P ≤ 0.05) decreased by about 25%, 50%, 31%, 55%, and 41% by applying PNB at ratio of 6%. Furthermore, in the same treatment group (PNB-6%), the significant (P < 0.01) decrease in Cr (62%), Ni (44%), As (43%), Cd (41%), and Pb (44%) bioaccumulation was detected in Brassica oleracea L. shoots. In the treatment group of RSB-6%, B. oleracea antioxidant enzymes such as superoxide dismutase (SOD), guaiacol peroxidase (POD), and catalase (CAT) declined significantly (P ≤ 0.05) by about 68%, 55%, and 38% respectively. A statistically highest significant (P ≤ 0.05) increase in concentration of chlorophyll a, b (125%, 350%) and carotenoid (166%) was found in the B. oleracea shoots treated with the highest ratio of PNB (6%). Leaf soluble protein significantly (P<0.01) raised by about 50%, 100%, and 250% in the B. oleracea grew in the soil treated with PNB at the ratio of 2%, 4%, and 6%, respectively, while leaf soluble proline and sugar concentrations significantly (P ≤ 0.05) declined by about 40%, 60%, and 80% as well as 30%, 50%, and 70%. The results suggested that PNB-6% was the best acidic soil amendment among the tested treatment. However, larger-scale studies are needed to verify the effects of PNB on plant growth, toxicity, and soil properties in diverse environmental conditions before widespread agricultural application.