Quality Evaluation of Biochar Prepared from Different Agricultural Residues

Biochar gained recognition as an efficient material for carbon sequestration and soil fertility. For its suitable application, it is important to know its chemical and physical properties which depend on the type of the initial material used. Agricultural residues of different types (e.g., Sesbania stems (Sesbania punicea, SS), Chickpea plant (Cicer arietinum, CP), Maize cobs (Zea Mays, MC), Wheat straw (Triticum aestivum, WS), Sugarcane (Saccharum officinarum) bagasse (BG) and Animal dung (AD) were pyrolyzed at temperature range of 300-500 °C in order to compare the biochar samples obtained on the base of its physical and chemical properties. Physico-chemical characteristic such as pH, EC, proximate composition, macro and micronutrients, surface functional groups identification by Fourier Transform Infrared spectroscopy (FTIR) and structure morphology by Scanning Electron Microscope (SEM) were carried out in biochar samples by using standard methods. Statistical analysis of the data revealed significant difference for proximate composition, pH, EC and macro and micro nutrients. Biochar obtained from Sesbania stem was found high in fixed carbon content (66.9%) and volatile matter (27%) but low in ash content (4.5%). AD biochar contained lowest amount of fixed carbon (49%) and volatile matter (17%) but highest ash content (30%) among different biochar samples under investigation. All the samples were alkaline in nature with substantial values for electrical conductivity. Macro and micronutrients such as Zn, Mn, Mg and P were high (19.6, 20.4, 37.31 and 237 mg L^-1, 510 mg 100g^-1 respectively) in AD biochar while minimum values for Mn, Cu, P and Na (12.0, 20.4 mg L^-1, 150 and 38 mg 100g^-1) were noticed in SS biochar samples. All the biochar samples were highly porous except AD and MC biochar samples. The most abundant functional groups found in spectra of all biochar samples were C=C aromatic and O-H except in MC biochar. It was concluded from the results that being highly porous in structure, high in carbon content and containing all the identified functional groups, SS biochar was found the best to be used as soil amendment that could have positive effect on improving the soil health. Moreover, the animal manure is recommended to be used as manure in soil rather than converted to biochar.