SEQUENTIAL CHEMICAL FRACTIONATION AS A TOOL FOR ACCESSING THE ORGANIC MATTER IN BIOCHAR

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This contribution is focused on in-depth characterization of biochar – one of the possible solutions how to improve soil properties and soil fertility. For these purposes a sequential chemical fractionation method to determine the organic matter content, its distribution in biochar was utilized. This sequential chemical fractionation procedure was used to reveal the content of organic matter in different biochar samples with different properties (samples with European biochar certification for usage in agriculture) which depend significantly on the source material used for biochar production as well as on the conditions used during biochar production (e.g., pyrolysis temperature and residence time). In parallel, these samples were also fractionated by classic alkaline extraction to obtain the so-called extractable fraction of organic matter (NOM). In recent years, increasing demands have been placed on crop yields which also create increased demands on soil fertility. For these reasons, various substances are often added to the soil artificially to increase fertility. They are most often classical inorganic-based fertilizers. Recently, however, research has also focused on the application of alternative additives to soils in order not only to increase fertility but also to improve the physicochemical properties of the soil and to increase the content and stabilization of soil organic matter. These additives are often included in a group called – soil supportive substances (SSS). Substances that are widely used for application include, for example, lignite fly ash, biochar, hydrosorbents, lignite and a mixture of fractions of humic substances. It is also very important to apply a suitable form with a given particle size, internal structure, and morphology (porous structure). Biochar is one of the important soil conditioners having positive effect on crop yield, soil quality, nutrient cycle, and carbon sequestration due to the transfer of organic carbon from it to the soil. It is kind of a charcoal mostly produced by pyrolysis of biomass in absence of oxygen. Biomass can be considered an excellent source material, as it is renewable and includes many things that are often considered waste. It is a stable, solid and carbon rich substance that can endure in soil for thousands of years. However, the effect depends on the properties of the biochar, its doses to the soil, but also on the properties of the soil itself. Despite of some authors pointing out a possible negative effect, it is necessary to perform its depth characterization to be able to predicts its role in soil and its optimal application dose Individual fractions obtained from sequential chemical fractionation as well as NOM samples were characterized by methods of elemental analysis (determination of organic elements content), thermogravimetry (contents of ash, organic matter, and moisture). The results showed that the method of sequential chemical fractionation gives higher yields of organic matter compared to classical alkaline extraction. Moreover, the obtained fractions divided according to solubility and strength of binding to residual inorganic matter of biochar can be better characterized by physical-chemical methods, which provides more detailed information about organic matter in biochar and its possible effect on soil properties.

Biochar; fractionation; organic matter; extraction

ŠIRŮČEK, D.; KALINA, M.; KLUČÁKOVÁ, M.

6. 8. 2023

Pontificia Universidad Católica de Chile

Jaime Guzmán Errázuriz 3300, Providencia, Santiago, Chile

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