The Preliminary Study of Water-Retention Related Properties of Biochar Produced from Various Feedstock at Different Pyrolysis Temperatures

Physicochemical properties of biochar, which are used as a soil amendment material in agricultural fields, are different depending on biomass feedstock and pyrolysis processes. In this study, we evaluated the influence of feedstock type and pyrolysis temperature on the water-retention related properties of biochar. Wood-chips [cedar (CE) and cypress (CY)]; moso bamboo (MB); rice husk (RH); sugarcane bagasse (SB); poultry manure (PM) and agricultural wastewater sludge (WS) were each pyrolysed at 400, 600 and 800 °C with a retention time of two hours. Scanning electron microscopy micrographs (SEM), hydrophobicity indices, pore-size distribution measured by mercury-intrusion porosimetry, water-retention curves (WRCs) and plant-available water capacities (AWCs) of the biochars were measured to evaluate their potentials as soil-amendment materials for improving soils’ water-retention. As the pyrolysis temperature was increased, the hydrophobicity index decreased. On the other hand, pyrolysis temperature did not affect the distribution of micrometre-range pores, which are useful for plant-available water, of biochars. The AWCs of the biochars formed from CE, CY and SB were greater than those produced from other feedstocks, at 600 and 800 °C. Therefore, we can suggest that the biochars derived from wood-chips (CE and CY) and SB have greater potential for enhancing soils’ water-retention.