Physical and chemical characterization of biochars derived from different agricultural residues

TLDR

Biochar is widely recognized for carbon sequestration and soil fertility, but its chemical and physical properties—dependent on feedstock and pyrolysis conditions—must be understood to select optimal applications. The study aimed to optimize the physicochemical properties of biochar as a soil amendment by pyrolyzing various agricultural residues at temperatures ranging from 400 to 800 °C. The authors pyrolyzed rice husk, rice straw, apple wood chips, and oak wood chips at 400–800 °C to produce biochars with varying physicochemical traits. Low‑temperature pyrolysis yielded high biochar amounts, while high temperatures produced biochars with higher carbon content, larger surface area, and stronger adsorption; 600 °C biochars were more recalcitrant, 400 °C retained volatile compounds; rice‑derived biochars had high yields and silica‑enriched chemistry, whereas wood‑derived biochars had high carbon and adsorption capacity. Abstract.

Abstract

Abstract. Biochar is widely recognized as an efficient tool for carbon sequestration and soil fertility. The understanding of its chemical and physical properties, which are strongly related to the type of the initial material used and pyrolysis conditions, is crucial to identify the most suitable application of biochar in soil. A selection of organic wastes with different characteristics (e.g., rice husk (RH), rice straw (RS), wood chips of apple tree (Malus pumila) (AB), and oak tree (Quercus serrata) (OB)) were pyrolyzed at different temperatures (400, 500, 600, 700, and 800 °C) in order to optimize the physicochemical properties of biochar as a soil amendment. Low-temperature pyrolysis produced high biochar yields; in contrast, high-temperature pyrolysis led to biochars with a high C content, large surface area, and high adsorption characteristics. Biochar obtained at 600 °C leads to a high recalcitrant character, whereas that obtained at 400 °C retains volatile and easily labile compounds. The biochar obtained from rice materials (RH and RS) showed a high yield and unique chemical properties because of the incorporation of silica elements into its chemical structure. The biochar obtained from wood materials (AB and OB) showed high carbon content and a high absorption character.