Aging of biochar in soils and its implications

Authors: PIGNATELLO, JOSEPH - Connecticut Agricultural Experiment Station; Uchimiya, Sophie; ABIVEN, SAMUEL - University Of Zurich

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 9/6/2023
Publication Date: 6/2/2024
Citation: Pignatello, J.J., Uchimiya, M., Abiven, S. 2024. Aging of biochar in soils and its implications. In: Lehmann, J., Joseph, S., editors. Biochar for Environmental Management. 3rd edition. London: Routledge. p. 249-276. https://doi.org/10.4324/9781003297673-10.
DOI: https://doi.org/10.4324/9781003297673-10

Interpretive Summary: Numerous studies have been conducted in the past 10 years on the environmental fate of biochar. Those efforts included changes in biochar itself, and its interactions with metals and organic compounds in soils. This chapter will offer mechanistic insights and fundamental chemistry concepts for end-users interested in biochar.

Technical Abstract: This chapter will address natural or simulated natural aging processes on biochars and chars and their effects on sorption and reactivity towards organic and inorganic compounds. The subject matter was reviewed in the Chapter 10 of the second edition of this book (Pignatello et al., 2015a), and the present chapter will revise and update findings reported therein and discuss new findings. The term soil will refer to vadose zone soils unless otherwise stated. Except where indicated, the biochars referred to in this section were made by slow pyrolysis, with the final heat treatment temperature indicated where necessary. This chapter will not address mineralization of biochars and chars, the effects induced by aging on priming or organic matter decomposition, microbial communities, greenhouse gas emissions, soil-plant interactions, and C,P,N cycling. Long-term biochar stability per se is an important issue in regard to carbon sequestration potential and greenhouse gas emissions (Leng et al., 2019), but is not covered here. Since the Chapter 10 of the 2nd edition (Pignatello et al., 2015a), some aspects of the subject matter have been reviewed (Mia et al., 2017; Wang et al., 2020). The Chapter 10 of the 2nd edition concluded that an understanding of the chemical alteration of biochar in soil is constrained by the analytical methods in use. Consequently, we still do not completely understand the processes and mechanisms leading to the chemical alteration of biochar in soil, including how oxidation and functionalization happen or how biochar, how mineral and organic matter interact, and how changes induced by aging affect sorption and reactions with small molecules. Since then, the literature has expanded tremendously and many mechanistic aspects of aging and its consequences have come more closely into focus. We begin by dealing with the keystone issue of how best to determine aging effects experimentally.