Mitigating Heavy Metal Toxicity In Maize Under Contaminated Soil Using Spent Mushroom Substrate Biochar And Growth-Promoting Rhizobia

Abstract

Soil heavy metal toxicity has been rising worldwide, and bioremediation via sustainable and recalcitrant materials has been put into the spotlight in recent years. A pot experiment was carried out in the glass house of the Department of Soil and Environmental Sciences, The University of Agriculture, Peshawar to investigate the effect of spent mushroom substrate (SMS) biochar and plant growth promoting rhizobia (PGPR) under Cd and Pb contaminated soil. The experimental design was completely randomized design with seven treatments and three replications. The treatments consisted of contaminated soil with Cd (20mg kg-1 soil) + contaminated soil with Pb (20mg kg-1 soil) + PGPR + SMS biochar (0.5, 1, 1.5 and 2% with PGPR). The use of PGPR with 2 % SMS biochar resulted in significant increase in plant height 38.7 %, shoot dry weight 37.5 % and root dry weight 67.8 % than the contaminated control. The concentration of Cd in roots and shoots was higher in contaminated soil without biochar; root and shoot Cd concentrations were reduced by 54 and 73% respectively with PGPR amended with 2% SMS biochar and 62 and 67% respectively in contaminated soil without PGPR. The chlorophyll content also significantly improved with PGPR and SMS biochar by 5-43% over the contaminated control. Moreover, application of 2% biochar in combination with PGPR decreased the AB-DTPA extractable Cd and Pb in soil by 52 and 44%, respectively. The soil organic matter and nutrient contents were also enhanced under PGPR and biochar. The results offer a sustainable solution to decontaminate Cd and Pb toxic soils and enhance the growth of maize and soil fertility.