Effects of feedstock type, production method, and pyrolysis temperature on biochar and hydrochar properties

•Higher temperatures produced higher thermal stability biochars.•Production method showed strong effect on biochar properties.•Biochars showed no statistically significant effects on plant. This work explored the effect of temperature, production method, and feedstock type on the physicochemical and biological properties of biochars and hydrochars. Biochars and hydrochars made at lower temperatures had higher production rates. Higher pyrolysis temperatures not only increased carbon content of biochars but also produced higher thermal stability biochars that did not start to decompose in air after 400–450°C. The production method showed strong effect on biochar properties. Compared to the dry-pyrolysis biochars derived from the same feedstocks, the hydrochars had more acidic pH values and lower carbon contents. The results showed that feedstock types could also influence characteristics of the biochars. None of the chars showed statistically significant effects on plant seed germination and seedling growth and thus could be used as soil amendments. Our findings indicated that biochars with different properties could be developed by changing production conditions to better satisfy their environmental applications.