A Deep Study on Connections Between Soil Aggregation, Pore Space, and Chemical Composition

ABSTRACT

The vast range of sizes at which aggregation occurs and the diversity of aggregation variables contribute to the lack of understanding of the relationships between soil structure and physical-chemical soil attributes. We gathered information on 127 soil samples from three European Critical Zone Observatories, including aggregate fractions, soil porosity, texture, and chemical soil parameters, to better comprehend these processes. The mechanisms connecting porosity and aggregates were first evaluated. The percentages of both DSA (dry sieved aggregates) and WSA (water stable aggregates) did not correlate with one another. Although the association between aggregate abundance and soil microporosity and micro + mesoporosity was strong for the WSA fraction, it was not as strong for the other fractions. Although the proportion of DSA had no effect on the soils total porosity, it did have an effect on the ratio of micro- to mesopores (30 kPa/0.25 kPa), indicating that micropores are mostly situated within DSA and mesopores are positioned between DSA and loose particles. Second, we looked into how chemistry and physics influence soil composition. Both the WSA and DSA fractions were only mildly affected by the soil texture, whereas the concentration of Fe- (hydr)oxide was favourably linked with the WSA fraction and with the porosity of the soil. The presence of Fe- (hydr)oxides on bigger minerals may be to blame for this phenomenon because they serve as adsorption sites for organic compounds, allowing even poorly reacting mineral particles to be absorbed by the organic network. Decreases in soil pH and increases in SOC and Fe-(hydr)oxides content led to a higher proportion of WSA. Organic coatings on particles aid in coagulation in acidic conditions, which explains this pH impact. Soil chemical characteristics, aggregate formation, and soil porosity were all shown to have mechanistic links between them in this study.

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