Humus Substances and Soil Structure

Abstract In this study, the soil structure of two soil types (Haplic Chernozems and Eutric Fluvisols) in four ecosystems (forest, meadow, urban and agro-ecosystem) with dependence on humus substances were compared. The stability of dry-sieved and waterresistant macro-aggregates and micro-aggregates with a dependence on the proportion of humus substance fractions was determined. Quantity of humus substances influenced mainly water-resistant aggregates. A positive correlation was recorded between size fraction of 2.3 mm and contents of humus substances (P < 0.01; r = +0.710) and fulvic acids (P < 0.05; r = +0.634), and negative correlation between size fraction of 0.5.1 mm and contents of humus substances (P < 0.05; r = -0.613) and fulvic acids (P < 0.01; r = -0.711). Humic acids influenced mainly the formation of dry-sieved aggregates and fulvic acids played an important role in micro-aggregate formation. The quality of humus substances influenced more intensively the formation of dry-sieved aggregates. There were positive correlations between optical parameters of humus substances and humic acids and larger dry-sieved aggregates (3.7 mm) and negative correlations with smaller (0.5.3 mm). The highest proportions of larger size of water-resistant aggregates (1. 20 mm) were in forest ecosystem, but smaller (0.25.1 mm) agreggates were dominated in agro-ecosystem.