Black Gold from the Fields: Obtaining Pyrolytic Biochar from Agricultural Wastes at Various Pyrolysis Temperatures

India produces a large amount of agricultural residues, traditionally disposed of through open burning. Such practices have negative health and environmental impacts. Converting waste via pyrolysis into biochar offers a sustainable strategy for enhancing soil fertility, carbon sequestration, and resource recovery. Although many studies have examined the influence of pyrolysis temperature on biochar properties, most focus on feedstocks like rice husk and woody biomass, with little attention given to underused residues such as finger millet husk. This study evaluated four agricultural residues, finger millet husk, rice husk, sawdust, and hardwood, depolymerized at 300, 400, 500, and 600°C, respectively. The resulting biochars underwent proximate and ultimate analysis, physicochemical characterization, and assessments of pore size and surface morphology. Results showed that increasing pyrolysis temperature reduced biochar yield and volatile matter, while increasing fixed carbon, pH, organic carbon content, porosity, and surface area. Variations also depended on feedstock composition. Biochar from finger millet husk at 300°C was flaky, chemically active, and suitable for microbial colonization, whereas hardwood biochar at 600°C was highly carbonized, porous, stable, and effective for pollutant adsorption and long-term carbon sequestration. This research introduces finger millet husk as a novel biochar precursor, linking specific properties to potential agricultural and environmental applications. Additionally, the study emphasizes how pyrolysis temperature influences biochar characteristics and their practical uses.