The Proportion of Soil Aggregates in Dependence on the Fraction Composition of Humic Substances

Humic substances (HS) are an important stabilizing element in the formation of soil aggregates. The experiment included 6 soil types (Haplic Fluvisol, Haplic Chernozem, Cutanic Luvisol, Haplic Cambisol, Haplic Planosol, Rendzic Leptosol), each in four types of ecosystems (forest, meadow, urban, and agro-ecosystems). Soil macroaggregates were separated with the sieve (dry and wet sieve) to size fractions of net aggregates; humic acids (HA) and fulvic acids (FA) were divided into 3(4) fractions: free and bound with mobile R2O3, bound with Ca2+, and bound with mineral components and stable R2O3. The influence of HA and FA fractions on the proportion of dry-sieved macroaggregates (DSA) and wet-sieved macroaggregates (WSA) was different. Mainly HA bound with polyvalent cations had a positive influence. In the case of HS, their influence depends also on the components with which HA and FA are bound. WSA of the 0.5-1 mm size fraction that is an important indicator of changes in ecosystems, had a higher proportion in the ecosystems influenced by man (agro-ecosystem > urban >) than in the ecosystems close to nature (> meadow > forest ecosystems). The influence of ecosystem was reflected in the proportion of those fractions of DSA and WSA on which the effect of soil type and HS was not shown, and vice versa.