Impact of different feedstocks derived biochar amendment with cadmium low uptake affinity cultivar of pak choi (Brassica rapa ssb. chinensis L.) on phytoavoidation of Cd to reduce potential dietary toxicity

Biochar has become eco-friendly amendment used for phytoavoidation with low cadmium (Cd) accumulating cultivars of crops to ensure food safety in Cd contaminated soils. In this study, biochar with different waste feedstock material were evaluated for their effectiveness on essential trace metals mobility, Cd bioavailability and its accumulation in two contrasting Cd accumulating cultivars of pak choi (Brassica rape ssp. chinensis L.) grown in Cd contaminated Mollisol soil. A greenhouse experiment was conducted with plants grown in Cd contaminated soil that had been amended with biochar derived from barley straw, tomato green waste, chicken manure, duck manure and swine manure at application rate of 0%, 2.5% and 5.0% (w/w). The results showed that soil pH was significantly increased by all treatments. Biochar increased plant dry biomass, micronutrients bioavailability with significant differences in the Cd sorption capacity, with the effectiveness higher with increasing biochar application rate. However, tomato green waste (TGW) and chicken manure (CM) derived biochar were more effective than the other biochar in reducing Cd mobilization in soil by 35-54% and 26-43% and reduced its accumulation in shoots of pak choi cultivars by 34-76% and 33-72% in low Cd accumulator cultivar and 64-85% and 55-80% in high Cd accumulator cultivar than the control. Overall, results indicate that TGW and CM biochar can efficiently immobilize Cd, thereby reducing bioavailability in Cd contaminated Mollisol soil to ensure food safety.