Influence of temperature and residence time on characteristics of biochars derived from agricultural residues: A comprehensive evaluation

Abstract In this study, the influence of production conditions (i.e., pyrolysis temperature and residence time) on the fundamental properties and the nutritional traits of biochars derived from different feedstocks (corn stalk, rape straw, wheat stalk, and peanut shell) were investigated. The results showed that pyrolysis temperature was a critical parameter affecting biochar properties, whereas the influences of residence time and feedstock were comparatively weaker. Biochar properties, including the pH, ash content, electrical conductivity (EC), oxidation stability, and the ability to retain nutrients, were positively related with increasing temperature and prolonged residence time. However, the water-extractable organic matter and available nutrients were negatively related with temperature and residence time. There was a minimal release of NH4+-N, NO3−-N, and PO43−-P from the generated biochars, and their concentrations were reduced through carbonization. By comparison, the water-soluble K+ content steadily increased with pyrolysis. Generally, the biochars showed a limited capacity for sorbing PO43− and NO3−, although the removal efficiencies were enhanced by pyrolysis. By comparison, higher NH4+ removal was achieved by biochars, and particularly for biochars with a higher pH. These findings suggest that the application of agricultural residue-derived biochars might not provide plants with sufficient nutrients (except for K). Additionally, the biochars generated at 500 °C for a duration of 1 h demonstrated higher potential for carbon sequestration.