Revitalizing cadmium-stressed sunflower: co-composted biochar improves growth, antioxidant responses, and soil...

Heavy metals especially cadmium (Cd), has become a matter of concern for environmentalists due to extensive industrialization and poor management of industrial waste. As a toxic pollutant, Cd has ability to deteriorate soil quality and hence disturbs the plant growth and yield. Co-composted biochar (COMBI) has been reported as an excellent organic amendment for improving soil quality, crop productivity and amelioration of heavy metals polluted soil. Therefore, an experiment was performed to assess the potential of co-composted biochar to enhance sunflower growth under Cd stressed soil. Different concentrations 0, 30 and 60 mg kg^-1 Cd and normal, modified and co-composted biochar at the rate of 1% (w/w) were applied to soil.

The application of normal and modified biochar considerably improved the sunflower growth, yield, physiology and biochemistry and decreased the Cd uptake in plant tissues. Among applied amendments, co-composted biochar showed better results, by increasing the crop agronomic parameters ranging from 115 to 132%, as compared to control treatment under Cd stress. The chlorophyll content, water use efficiency (WUE), photosynthetic rate (A), transpiration rate (E), stomatal conductance (gs), sub-stomatal conductance (Ci), relative water content (RWC), and electrolyte leakage (EL) were improved by 122, 117, 126, 133, 128, 131, 123, and 121%, respectively, when co-composted biochar was used compared to the control. Moreover, stress related metabolites and antioxidant enzyme essays showed increase in proline content, soluble sugars, lipid peroxidation, catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD) and glutathione reductase (GR) by using co-composted biochar by 123, 121, 118, 128, 124, 133 and 126%, respectively, in Cd (60 mg kg^-1) contaminated soil. In addition to this, a prominent reduction in accumulation of Cd in the root (66%), shoot (77%) and grain (94%) was observed due to its immobilization in soil (121%) under the influence of co-composted biochar application.

The results of this study revealed that application of biochar could improve crop growth and immobilize Cd in soil and co-composted biochar could be adopted as a better strategy to remediate the heavy metal stressed soils. It can be considered as an effective practical approach to transform agricultural waste materials into organic soil amendments to be applied for sustainable agricultural practices in polluted soil.