The research was carried out on an irrigated stationary crop rotation of the Federal State Budgetary Scientific Institution "Omsk Agrarian Research Center" in the southern forest-steppe of Western Siberia. The aim of the research was to establish the direction and intensity of mobilization biological processes in case of long-term irrigation, their quantitative characteristics, as well as possible adverse changes of biological (ecological) properties of meadow – black soil. The microbial

more »

... ty performs the function of maintaining soil homeostasis, therefore it quickly responds to habitat changes. The intensity of soil mineralization and humus formation processes was determined by a combination of fertilization and irrigation factors. It was found that immobilization processes prevailed in the soil under crops. The highest coefficient of organic matter transformation, i.e. transformation increase of plant residues into organic matter, was noted when introducing nitrogen-phosphorus fertilizers for barley crops. Application of mineral fertilizers promoted an increase of the number of the defined microorganisms, enhanced cellulose decomposition in the soil, potential capacity of soils to accumulate nitrate and enzyme activity, which ultimately increased the yield of cultivated crops. The yield of perennial grasses on a fertilized background was at the control level due to loss of legumes (goat's rue) and predominance of bluegrass species (awnless brome). A strong correlation was obtained between the intensity of cellulose decomposition in the soil, nitrification capacity and crop yields (r = 0.67 ± 0.28 and 0.91 ± 0.16, respectively). Long-term irrigation of meadow-black soil did not have a negative impact on its ecological state, and usage of intensive cultivation technology of crops in crop rotation stimulated an increase of soil microorganisms and their activity.