An investigation into the reactions of biochar in soil

TLDR

Interactions between biochar, soil, microbes, and plant roots can occur rapidly after application, yet the extent, rates, and implications of these interactions remain poorly understood. This review seeks to describe biochar properties, propose potential post‑application reactions, and recommend experimental trials to evaluate their influence on soil amendment efficacy and carbon sequestration. The review outlines dissolution–precipitation, adsorption–desorption, acid–base, and redox reactions, emphasizing pore‑level processes and interactions with roots, microorganisms, and soil fauna. Studies of chicken‑litter, green‑waste, and paper‑mill‑sludge biochars weathered for 1–2 years in an Australian Ferrosol confirm some of these mechanisms and show that the resulting interactions are both biochar‑ and site‑specific.

Abstract

Interactions between biochar, soil, microbes, and plant roots may occur within a short period of time after application to the soil. The extent, rates, and implications of these interactions, however, are far from understood. This review describes the properties of biochars and suggests possible reactions that may occur after the addition of biochars to soil. These include dissolution–precipitation, adsorption–desorption, acid–base, and redox reactions. Attention is given to reactions occurring within pores, and to interactions with roots, microorganisms, and soil fauna. Examination of biochars (from chicken litter, greenwaste, and paper mill sludges) weathered for 1 and 2 years in an Australian Ferrosol provides evidence for some of the mechanisms described in this review and offers an insight to reactions at a molecular scale. These interactions are biochar- and site-specific. Therefore, suitable experimental trials—combining biochar types and different pedoclimatic conditions—are needed to determine the extent to which these reactions influence the potential of biochar as a soil amendment and tool for carbon sequestration.