Biochar-amended nutrient film technique flow system effectively alleviated chromium stress in guar (Cyamopsis tetragonoloba) plants

Heavy metal contamination, such as chromium (Cr), poses global threats to soil, water, and human health. Biochar is an effective adsorbent for mitigating heavy metal toxicity, remediating polluted environments, and promoting plant growth under stress. This study evaluated the effects of Allium sativum peel biochar, produced via concentrated sulfuric acid carbonization (CSGPB) and high-temperature carbonization (HTGPB), on Cyamopsis tetragonoloba under Cr-stress in a Nutrient Film Technique (NFT) hydroponic system. The results showed that combining two biochar treatment showed better results in mitigating the growth of guar plants under Cr-stress. Increasing the pH and EC values of water reduced the mobility and plant availability of the heavy metal chromium, resulting in an 87.78 % reduction of Cr in guar, along with enhanced antioxidant enzyme activities, alleviation of oxidative stress, improved nutrient absorption, primary metabolite synthesis, and soluble sugar and protein levels, and significant growth promotion with a 123.8 % increase in biomass. This study underscores the potential of biochar (CSGPB-HTGPB) as a high-performance adsorbent for remediating Cr-contaminated water in flow-through systems, offering a theoretical basis for addressing heavy metal pollution. • Biochar mitigates Cr toxicity, remediates contamination, and promotes plant growth under stress conditions. • HTGPB increased water pH by 19.28 % and electrical conductivity by 17.73 % under chromium stress. • Combined biochar treatment improved guar length by 12.18 % and boosted biomass by 123.80 %. • Cr stress elevated SOD (35.25 %), POD (127.80 %), and CAT (112.21 %) with biochar application. • Biochar enhanced nutrient uptake and metabolite synthesis in guar under chromium stress.