Biochar-Assisted Bacillus Inoculation Reduces Cadmium And Lead Bioavailability And Enhances Maize Growth In Contaminated Soil

Abstract

Cadmium (Cd) and lead (Pb) in agricultural soil are harmful and interfere with the growth of the crop, with the possibility of increasing the amount of metal in the food chain. To assess the growth promoting potential of heavy-metal-tolerant Bacillus strains (HMTBS) and the possible reduction of Cd and Pb bioavailability by combining HMTBS with biochar, a glasshouse pot experiment was carried out at the Department of Soil and Environmental Sciences, The University of Agriculture, Peshawar. Three bacterial strains (Bacillus pumilus, Bacillus proteolyticus and Bacillus paramycoides) were used along with four different rates of biochar (0, 1, 1.5 and 2%). Cultivar of maize, Azam, was cultivated under Cd and Pb stress and plant growth, AB-DTPA extractable soil metals, metal concentration of the shoots and roots, metal uptake and translocation factors were determined. The application of biochar always showed a positive effect on growth and reduced metal availability. In both bacterial strains, the plant height under 2% biochar grew from 87 cm to 102 cm, shoot dry biomass grew from 82.2 to 94.0 g pot-1 and root dry weight increased from 3.31 to 5.21 g pot-1 in comparison with 0% biochar. This 2% rate of biochar decreased the concentration of AB-DTPA extractable Cd from 7.16 to 1.92 mg kg-1 and Pb from 8.15 to 3.00 mg kg-1. Shoot Cd and Pb decreased from 8.34 to 3.37 mg kg-1 and from 8.44 to 3.21 mg kg-1, respectively. The tested strains showed varying abilities to decrease Cd and Pb concentration in the tissues of plants and soil; B. paramycoides had the highest reduction potential and B. proteolyticus had the highest mean shoot biomass. The results suggest that the use of metal tolerant Bacillus spp. with 2% biochar is a potential, low cost, and environmentally friendly method for enhancing maize growth in Cd and Pb polluted soil.