**3.3 Biochar**

The biochar is highly aromatic, where the functional groups associated with it, which give the biochar a net negative charge, resulting in increased CEC in soil with increased adsorption capacity for both organic and inorganic compounds, and greater nutrient retention. Biochar has a porous body, charged surface, and many different surface functional groups and contains significant amounts of humic and fulvic-like substances [47]. It has also been used to remediate heavy metals from soils and water. Different kinds of biochar derived from plant residues and animal manures are used to reduce the mobility and availability of metal in contaminated soil and water. Mostly biochars are alkaline in nature and released the available form of P, K, and Ca. In general, application of biochar reduced the concentrations of zinc and cadmium by 45 and 300 fold [48]. It is due to sorption mechanism which is used for the withholding of metals by biochars. The Cu leaching was correlated with higher DOC contents [49]. Biochar, when applied to the soil, improves quality and productivity of soil because the oxides, hydroxides, and carbonates present in biochar can act as liming agents [50]. Biochar can reduce soil bulk density and thereby increases water infiltration, soil aeration, root penetration, and increase soil aggregate stability. Biochar spiked soil has soil pH > 7 which is found suitable for the rise of fungal hyphae. Adding higher amounts of biochar to soil increased the environment for microbes, with promoted growth via increased porosity [51]. Therefore, it is critical to consider both soil and biochar properties when it is used for the remediation of salt-affected soils and the source of the feedstock used to produce the biochar which is used as an organic amendment [52]. Generally, biochar application could be recommended as an appropriate amendment for in-situ remediation and immobilization of the heavy metals especially for lead and cadmium in contaminated soils [53].
