The objective of the research is to investigate the main indices of soil fertility of steppe zone chernozems, such as humus content in soil profile and its qualitative composition by Tyurin’s method, pH, hydrolytic acidity, and the content of exchangeable calcium, magnesium, and sodium. The study was carried out in Voronezh region in Talovskiy and Bogucharskiy districts, city Rostov-on-Don (Botanic garden of the South Federal University), and Kushchevskiy district in Krasnodar region. It is established that potential fertility of chernozems and the depth of humus horizons are decreased while moving from the North to the South. Humus content and its changes in chernozems conform to the natural specifics, character, and duration of anthropogenic impact. Depending on the duration of plowing up, the changes in humus content agree with the pattern: the highest rate of humus content reducing is noted in the first years of chernozem use. The highest humus content was observed for the soils of fallow site in Kamennaya Steppe (9.77 %). The loss of humus was proportional to the duration of plowing up: after 20 and 50 years of using, the decrease was in 1.10 and 1.45 times, respectively. Humus content for the chernozems of Voronezh and Rostov regions was significantly lower (4.46 and 4.24 %, respectively). Soils of south facies were characterized by the higher values of pH which reach up to 8.2 in 40–50 cm soil layer. The main specifics and patterns of changes in soil exchangeable complex of chernozem soils were preserved for plowing and fallow lands; though, in arable soils of early period of use, the rise of exchangeable sodium content (up to 0.8–0.9 mmol/100 g) was observed. For fallow sites the higher values of acidity comparing to arable ones was marked. This phenomenon is provided by the impact of the little-transformed organic matter.
Keywords: chernozem, humus, exchangeable bases, medium reaction, fallow land, arable land.
