Changes in the Ratio of Aggregate Fractions in Humus Horizons of Chernozems in Response to the Type of Their Use

Data on the aggregate-size distribution (dry sifting method) in humus horizons of chernozems were processed by principal components analysis (PCA) with the centered logratio transformation of the initial data set. The analysis of the positions of treatments in the space of principal components coupled with the analysis of eigenvector magnitudes made it possible to identify several size fractions of aggregates, whose contents in the soils reflect soil degradation or progradation processes. These groups fitted well to the partial lognormal curves of aggregate sizes. In addition, the distribution of water-stable aggregates in coarse aggregate fractions (>10, 10-7, 7-5, and 5-3 mm) was analyzed. The integral analysis of the obtained data made it possible to propose the following conceptual model of the recovery of the structure of tilled chernozems. In the course of tillage, soil particles <0.25 mm in size are formed due to comminution. These particles are unstable and may stick together to shape large (>10 mm) water-unstable aggregates (clods). With the removal of tillage loads, large aggregates interact with fresh organic matter, and the water stability of aggregates increases. At the same time, the largest aggregates (mainly >10 mm) tend to transform into aggregates of smaller sizes.