Influence of biomass type and pyrolysis temperature on biochar characteristics for enhanced soil amendment

Biochar is a promising soil amendment, but its properties vary significantly based on biomass type and pyrolysis conditions. This study investigates the effects of feedstock type (sawdust, cotton stalk, reed cane, and sewage sludge) and pyrolysis temperature (400 −700 °C) on biochar yield and properties, focusing on chemical composition, and the effect of biomass chars on soil amendment for lettuce growth was determined with pot experiments. The results showed that the yield of biochar decreased geometrically with the increase of pyrolysis temperature, and the specific surface area and total pore volume of the all biochars increased, while the average pore diameter decreased. Sawdust, cotton stalk, and reed cane char exhibit well-developed aromatic porous structures and possess a higher carbon content. In contrast, sludge char had a comparatively lower carbon content, accompanied with high ash and nitrogen contents. Compared to control, the addition of biochar into soil significantly enhanced the plant growth. The maximum phytomass increases were 61.66 %, 81.81 %, and 101.41 %, with the addition of 3 % sawdust char, 3 % reed cane char, and 5 % sludge char, respectively. This observation may be benefited from the relatively higher specific surface area of reed cane char and the high C/N in sludge and sawdust char, improving the water retention, organic matter, and total nitrogen of soil. Conversely, the addition of more than 3 % cotton stalk char led to plant yield reduction and even death. This was due to the elevated levels of inorganic salts containing K and Na in the cotton stalk char.