Pyrogenic carbonaceous matter (PCM) is ubiquitous in the environment as a result of vegetation fires, but is also increasingly added to soil deliberately to improve its fertility, to remediate or to sequester carbon. Presence and additions of uncharred organic matter is known to change soil biogeochemistry. This contribution seeks to evaluate whether there are fundamental differences in which way charred organic matter additions change soil properties, suggests a conceptual framework of its direct and indirect influence, and discusses examples of PCM’s impact on soil carbon and nitrogen cycles. PCM defies easy categorization in terms of its effects on soil biogeochemistry, as production conditions, the type of organic matter that it was produced from and changes in the environment create a broad array of PCM properties. Nonetheless, some overarching trends exist in which way thermochemical conversion affects organic matter properties and its influence on soil. PCM from wood typically has greater surface area than the original organic matter with initially low amounts of polar groups. It therefore initially adsorbs little ammonium. Adsorption increases, however, with greater oxidation, which remains easily reversible. Although nitrate has been reported to be retained by PCM, the mechanism remains poorly studied and may relate to water retention in small pores in batch experiments and microbial immobilization in soils. Ammonia gas may interact with woody PCM, with strong effects of whether PCM is oxidized or not. PCM may increase and decrease mineralization of native organic matter in soil, and net effects depend on both soil properties and the type of PCM. In organic horizons, additions of either charred or uncharred organic matter may lead to so-called positive priming. In mineral horizons, however, PCM produced from wood typically elicits negative priming, whereas uncharred organic matter typically increases mineralization of native organic matter. Due to its persistent nature, woody PCM may on the short term decrease mineralization of existing organic matter by dilution, though long-term effects appear to be caused by surface interactions such as adsorption. Negative effects on microbial abundance do not appear to be important, though community composition may play a hitherto insufficiently explored role, albeit typically with less pronounced changes than as a result of additions of uncharred organic matter.<br/>

Pyrogenic carbonaceous matter interactions with inorganic and organic carbon and nitrogen

255th National Meeting (2018)

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