Biochars produced by slow carbonisation of three agricultural biomasses: physicochemical properties and potential for sustainable agro-environmental applications

Agricultural by-products, such as cashew nut shells (CNS), sorghum stems (SS), and corn stems (CS), constitute unutilized waste. However, these by-products can be used to produce biochar, which improves soil structure and fertility while contributing to water retention and carbon stability. The objectives of this research were to produce biochars from these three biomasses and to evaluate the physico-chemical characteristics of the biochars obtained [yield, pH, macro and micronutrient content, electrical conductivity (EC), infrared analysis (FTIR), specific surface area (SBET), morphology (SEM), and CHNS/O content]. A total of eighteen biochar samples were obtained by varying the carbonisation temperature (350 and 400 °C) and residence time (30, 60, and 120 min) in a muffle furnace. At a fixed temperature, yield decreases with increasing residence time, surface area, pH, and electrical conductivity. Among the eighteen types of biochar, the one derived from corn stalks had an apparent specific surface area of (35.07 m²/g). , followed by sorghum stalks (32.45 m²/g) and cashew nut shells (0.14 m²/g). The pH of the biochars is in the basic range (7.6–10.3). Furthermore, Krevelen's diagram reveals that biochars made from cashew nut shells are more stable in the long term, with the potential to persist for several centuries. These properties suggest that different types of biochar can be produced by adjusting production conditions and selecting biomass based on the soil characteristics in which it can be applied.