Stability of soil aggregates is affected by dozens different factors and their individual effects are hardly discernable. For this reason, we investigated the structure of the top layer (to a depth 0.2 m) of loamy soils (Haplic Fluvisol, Mollic Fluvisol and Calcaric Chernozem), at three sites (Šulekovo, Trakovice and Bučany) in the north-western part of the Danube Lowlands (Slovakia) in order to: (1) evaluate the differences in soil organic matter (SOM), texture, water-stable aggregates (WSA) and content of SOM in WSA; (2) determine the relationships between SOM, texture and WSA; and (3) identify the threshold limits for soil organic carbon (SOC) and the particle-size distributions for stabilization of water-stable macro-aggregates (WSAma). We found significant effects of a soil type on both SOM and WSA as well as on the content of SOM in WSA. When all loamy soils were assessed together, positive significant correlations were observed between size fractions of WSAma >2 mm and the content of SOC and hot-water soluble carbon (CHWD). The content of WSAma 1-0.25mm and water-stable micro-aggregates (WSAmi) correlated negatively with SOC and CHWD. The quality of SOM was more important than its quantity for the stabilization of WSAma at size fractions 1-0.25mm and WSAmi. The content of clay improved the aggregation in size fractions of WSAma >2 mm in the investigated top layer of loamy soils. The maximum WSAma content occurred where the ratio of organic carbon content in WSAma to that in soil was ~1.0. The threshold limits for clay and silt content for the formation of WSAma were ~20% and equal to 43%, respectively.

22.2.2017