Hybrid calcium bentonite–biochar composite enhances wheat productivity and resilience under combined cadmium and drought stress

Cadmium (Cd) contamination and drought stress are two frequently co-occurring abiotic stress in semi-arid agroecosystems, severely containing wheat productivity and food security. Present work evaluated the effectiveness of Calcium Bentonite (BENT), Wheat Straw Biochar (WSB) and Bentonite-Wheat Straw Hybrid Biochar (HBBC) for mitigation of Cd toxicity and water deficit stress in wheat. The wheat crop was grown in normal and Cd-contaminated soil (0 and 5 mg kg -1 Cd contamination) under well-watered (W-100%) and water deficit (W-50%) conditions. Across both water regimes, HBBC outperformed its individual amendments. Relative to Cd stress HBBC enhanced root and shoot dry weights by 41%, 29% and 36%, 43% grain yield by 40%, 73% and plant height by 51% and 40% in W-100% and W-50%, compared to respective Cd-5 controls. In addition to this, the HBBC reduced Cd concentration in root (-25%, -37%), shoot (-58%, -30%) and grain (-64%, 36%) under W-100% and W-50% compared to Cd-5 stress. These improvements were accompanied by improved physiological performance and reduced oxidative stress in wheat root and leaves experience water and Cd stress alone and in combination. Another aspect of higher HBBC performance compared to BENT and WSB is its role in better locking Cd in soil and reducing its uptake in both water regimes. Moreover, HBBC also remarkably enhanced grain nutritional acquisition resulting 86%, 22%, 59% higher N, P, K in grain in W-100% while 100%, 69%, and 67% increase in grain N, P, K under W-50% conditions. Overall HBBC proved to be an effective soil amendment for simultaneous Cd and water stress mitigation in wheat.