Purpose

Because the stability of soil aggregates is affected by many factors, we studied aggregates formed in forest and agricultural soils in different soil types (Cambisols, Luvisols, Chernozems). We evaluated: (1) the differences in water-stable aggregates (WSA) as related to soil type and land management and (2) the relationships between quantitative and qualitative parameters of soil organic matter (SOM), particle-size distribution and individual size classes of WSA.

Materials and methods

Soil samples were taken from three localities (Sobě?ice, Báb, Vieska nad ?itavou). Each study locality included both a forest and an agricultural soil-sampling area.

Results and discussion

We found that in forest soils, the proportion of water-stable macroaggregates (WSA_ma) relative to water-stable microaggregates (WSA_mi) was greater than in agricultural soils. When all soils were assessed together, positive statistically significant correlations were observed between the size classes WSA_ma > 1 mm and organic carbon (C_org) content; however, the WSA_mi content was negatively correlated with C_org content. Favorable humus quality positively influenced the stabilization of WSA_ma > 5 mm; however, we found it had a negative statistically significant effect on stabilization of WSA_ma 1–0.25 mm. In agricultural soils, the stabilization of WSA_ma was associated with humified, i.e., stable SOM. The WSA_ma content was highly positively influenced mainly by fulvic acids bound with clay and sesquioxides; therefore, we consider this humus fraction to be a key to macroaggregate stability in the studied agricultural soils. On the other side, all fractions of humic and fulvic acids participated on the formation of WSA_ma in forest soil, which is a major difference in organic stabilization agents of macroaggregates between studied forest and agricultural soils. Another considerable difference is that WSA_mi in agricultural soils were stabilized primarily with humic acids and in forest soils by fulvic acids. Moreover, in forest soils, a higher content of labile carbon in WSA had a positive effect on formation of WSA_mi.

Conclusions

The observed changes in individual size classes of WSA and interactions between SOM, particle-size distribution, and WSA have a negative impact on soil fertility and thereby endanger agricultural sustainability.