Mitigating the Toxic Effects of Chromium on Wheat (Triticum aestivum L.) Seed Germination and Seedling Growth by Using Biochar and Polymer-Modified Biochar in Contaminated Soil

This study compared the impact of biochar (in powder and extract forms) derived from the invasive tree Broussonetia papyrifera on the growth and eco-physiological responses of Vigna radiata (mung bean) under laboratory and experimental dome environments. The primary objective was to investigate the sustainable utilization potential of biochar derived from invasive plants. Powdered biochar was mixed into garden soil at amendment rates of 0.5%, 1%, 2%, and 4%, while for extract treatments, the seedlings were irrigated with extracts of these concentrations. The responses of plants were found to be dependent on the concentration and type of treatment (i.e., powder or extract) used. The highest levels of growth and eco-physiological responses were observed at a concentration of 1% for biochar extract and 2% for powdered biochar. In addition, the impacts were more pronounced in the roots than in the shoots. The biochar amendment resulted in a 7‒73% increase in root length and a 12‒148% increase in plant dry biomass when compared to the control. Crop growth, water use efficiency, and leaf area were greater in powdered biochar, but net photosynthesis (Pn), transpiration rate, and stomatal conductance were higher in plants treated with biochar extract. Adding powdered biochar to soil increases its pH, electrical conductivity (EC), moisture content, soil organic C, and amounts of available N, P, and K; however, the effects of applying biochar extracts were less pronounced. Crop growth and eco-physiological responses were found to be positively correlated, regardless of the biochar form used. Following biochar extract treatment, EC was found to be negatively correlated with Pn. The study revealed that powdered biochar had superior growth responses and soil improvement compared to biochar extract at higher concentrations. However, biochar extract also had comparable effects and can be beneficial in short-term cropping systems such as urban farming (e.g., in kitchen gardens and vegetable production) at lower concentrations (up to 2%). The findings of the study provide a baseline for future evaluations regarding the sustainable application of biochar liquor (water extract) as a source of nutrients and the powdered residual biochar as a potential material for adsorbing environmental contaminants or improving soil quality.

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