Influence of biochar and organic soil amendments on bioavailability and immobilization of copper and lead to common cocklebur in acidic sandy loam soil

Application of amendments may help to alter soil physicochemical properties and the bioavailability of metals. A pot experiment was carried out using a metal accumulator plant common cocklebur (Xanthium strumarium L.). The plant was grown in contaminated soil with copper (Cu) and lead (Pb) at four different concentrations of each metal (150, 250, 300, and 350 mg kg⁻¹ soil). Soil amendments hardwood biochar (HWBC), farmyard manure (FYM), and vermicompost (VC) were applied at 2.77 g kg⁻¹ rate. The amendments were effective in maintaining plant health under metal exposure. VC improved the chlorophyll stability index and dry biomass of plants, which was followed by FYM and HWBC. Decreased in peroxidase activity and metal concentration in plant tissues under the amendments disclosed their effectiveness to reduce metal toxicity. VC application reduced Pb concentration in plant up to 52.94%, while FYM reduced Cu uptake up to 30.03 % by the plant. The speciation study revealed the potentiality of the tested amendments to cause a reduction in bioavailable form of the metals. The order of efficiency to reduce exchangeable fraction of Cu was HWBC (29.2–69.0 %) > FYM (5.9–44.5 %) > VC (5.7–33.8 %). However, to reduce exchangeable fraction of Pb the order was VC (41.8–74.9 %) > FYM (30.2–60.0 %) > HWBC (18.5–26.9 %). Less bioavailable fractions (excluding exchangeable and carbonate bound) of Cu and Pb was found maximum at FYM and VC amendment respectively indicate higher efficacy of them to immobilize Cu and Pb in acidic sandy loam soil inducing reduce possibility of metal contamination in the food chain.