LAUSR

Contamination of agricultural soil with Cd has become a global concern because of its adverse effects on eco-health and food safety. Soil amendments with biochar have become one of the phytotechnology to reduce soil metal phyto-availability and their potential risk along the food chain. Biochar (BC), derived from cocoa-pod, was evaluated on soil Cd fractions (exchangeable, reducible, oxidisable and residual) by modified BCR sequential extraction and its efficacy to ameliorate Cd toxicity to soil enzymes and leaf bioactive compounds. A pot experiment was conducted using Cd-spiked soil at 10 mg/kg with tomato (Solanum lycopersicum L.) at BC applicate rate of 1 and 3% (w/w) for 6 wk. The addition of biochar significantly reduced (p<0.05) the exchangeable, reducible and residual fractions by at least ~23% with consequential decrease in Cd root uptake and transport within tomato tissues. The activity of soil enzymes (catalase, dehydrogenase, alkaline phosphatase and urease) was affected by Cd toxicity. However, BC application significantly enhanced the enzymes activities, especially at 3% (w/w) rate except for dehydrogenase. Toxicity of Cd was observed on glutathione, terpenoids and total phenols out of the studied secondary metabolites. However, BC application rate of 1% (w/w) significantly ameliorated the effect of toxicity on the secondary metabolites. In conclusion, the biochar demonstrated potentials to act as soil amendments for Cd immobilization and thereby reduced its bioavailability in soil to mitigate food security risks. This article is protected by copyright. All rights reserved.