Pyrolysis temperature changes the physicochemical characteristics of water hyacinth-based biochar as a potential soil amendment

Temperature greatly determines biochar’s physicochemical characteristics during the pyrolysis of a biowaste. This study aimed to investigate how pyrolysis temperature alters the physicochemical characteristics of water hyacinth (WH) biochar as a soil amendment. WH biomass was slowly pyrolyzed at three temperatures (350, 550, and 750 °C) for 2 h. Results show that biochar yield lessened from 51.0 to 33.3% with a temperature rise. When pyrolysis temperature increased biochar’s pH (9.24–11.2), electrical conductivity (28.0–44.7 mS cm −1 ), liming capacity (17.7–33.0% CaCO 3 equivalence), ash content (33.3–52.4%), available nutrients (Ca, Mg, K, P), surface area (1.1–29.8 m 2 g −1 ), pore volume, C/N ratio (15.9–20.3), and water holding capacity increased. However, C, H, N, H/C (0.89–0.11) and O/C (0.62–0.49) ratios, cation exchange capacity (CEC) (44.4–2.3 cmol + kg −1 ), and pore width decreased. Surface functional groups shrank when pyrolysis temperature increased. As the temperature rises, WH biochar becomes structured, porous, and recalcitrant. All WH biochar samples show high alkalinity, particularly developed at 550 °C and 750 °C could replace liming materials in soil acidity alleviation. Biochar produced at 350 °C and 550 °C could improve agricultural soil fertility and nutrient retention capacity due to the lower C/N ratio, high N content, and CEC. Biochar produced at 550°C and 750 °C can sequester carbon in the soil. Biochar developed at 750 °C be applied to amend soil physical properties due to its comparably high surface area and porosity. Hence, the thermal conversion of WH biowaste to biochar helps obtain suitable biochar properties for soil amendment.