Organic Matter of the Air-Dry and Water-Stable Macroaggregates (2–1 mm) of Haplic Chernozem in Contrasting Variants of Land Use

The content and the composition of soil structural units of different hierarchical levels were studied for Haplic Chernozems (Loamic, Pachic) of Kursk region under contrasting variants of land use (steppe and bare fallow). A detailed scheme of the method used to analyze the content and composition of organic matter in granulodensimetric fractions from the soil aggregates of different sizes and different water stability was developed. The major attention was paid to the study of aggregates isolated by the wet sieving method from the air-dry aggregates of 2–1 mm in size, as the most representative agronomically valuable aggregate fraction, Regardless of the land use, the content of the 2–1 mm air-dry aggretates was approximately the same in the soils under the steppe and the bare fallow. However, their water stability differed considerably between the steppe and the bare fallow. The long-term (52 yr) fallowing of the soil led to considerable losses of organic matter both in the whole soil and in different water-stable aggregates. Minimum losses were revealed for virtually all components of organic matter localized within undestroyed water-stable macroaggregates of 2–1 mm.