Associations Among Humus Substances, Exchangeable Cations, and Soil Texture Under Reduced and Conventional Soil Tillage Systems

Humus substances are an important part of stable soil organic matter, which is also influenced by the soil tillage system, particularly indirectly through the mechanisms of stabilisation. This study evaluated relationships within the humus substances–cations–soil texture system and differences between invasive and non-invasive tillage systems in four soils. The influence of exchangeable cations (K + , Na + , Ca 2+ , Mg 2+ , Fe 3+ , Al 3+ ) and particle size distribution (sand, silt, clay) on quantity (humic and fulvic acids) and quality (ratio of HA/FA, degree of humification, colour coefficients) of humus substances was studied. In reduced tillage, the humus substances interacted mainly with iron and aluminium. Higher humus substance contents were associated with higher K + ; the influence of Ca 2+ was greater in coarse-grain soils (Haplic Chernozem, Eutric Regosol); and Al 3+ was positively correlated with humic acids and negatively with fulvic acids. The statistical associations indicate that in conventional tillage, humus substances interacted mainly with Ca 2+ . Higher humic acid contents indicate an association pattern with higher Na + contents; the relationship of Ca 2+ appears more pronounced in fine-grained soils (Mollic Fluvisol, Haplic Luvisol); and Al 3+ was positively correlated with fulvic acids and negatively with humic acids. The soil tillage system influenced the humus substances indirectly by a combination of factors—cation composition and soil texture in different ways. In reduced tillage, clay and silt were statistically associated with iron and aluminium; in conventional tillage, there were two branches: clay with divalent cations and silt with trivalent cations. The soil tillage system can modify the impact of carbonates on humus substances and thus indirectly change the character of transformation processes in the soil. Depth is very important in evaluating the influence of the soil tillage system.