Biochar application improves lettuce (Lactuca sativa L.) growth in a lead-contaminated calcareous soil

Biochar, as soil amendment, can control the bioavailability of heavy metals in contaminated soils and reduce the risk of transferring heavy metals to the food chain. The objective of the study was to investigate the impacts of biochar derived from various wastes (apple pruning (AB), grape pruning (GB), or wheat straw (SB)) at 0%, 2%, and 5% w/w affecting lettuce growth and lead (Pb) phytoavailability in a Pb-contaminated calcareous soil. The plants were harvested 60 days after seeding and plant dry weight, Pb concentration, transfer factor (TF), biological concentration factor of shoot and root (BCF), and soil Pb phytoavailability were measured. At the highest Pb spiking, NH4NO3-extractable Pb was reduced by 24.6% and 51.8% at biochar rates of 2% and 5%, respectively, compared to the control. Application of biochar decreased Pb concentration in lettuce shoots, with the most significant reduction occurring by 5% of AB (44.0%), GB (30.5%), and SB (23.8%) at the highest level of Pb. The present findings provide novel evidence on the beneficial effects of the tested biochars, especially SB, on lettuce growth in a Pb-contaminated calcareous soil. Biochars could be used as an eco-friendly and cost-effective strategy for improving lettuce growth in metal-contaminated soils.