The biological activity of long-term irrigated meadow-chernozem soil under the conditions of intensive use

The article summarizes the data of long-term field experiments on irrigated meadow-chernozem soil in the southern forest-steppe zone of Omsk region. Aim of current research is to establish the direction and intensity of biological mobilization processes during long-term irrigation, their quantitative characteristics and possible adverse changes in the biological properties of meadow-chernozem soil. It was found that intensive irrigation does not affect negatively the parameters of soil biological activity. Moreover, in combination with nitrogen and phosphate fertilizers intensive irrigation stimulates the growth of microorganisms, enzyme activity, cellulose decomposition energy and other indicators, which all together increase the yield of cultivated crops. The intensity of mineralization processes and humus formation was mostly determined by combining nitrogen fertilization and irrigation. ASA/MPA ratio (ammonium starch agar/meat peptone agar) during irrigation and application of nitrogen fertilizers was greater than unity, which indicates the prevalence of mineralization processes in the soil. MPA/ASA (immobilization coefficient) equaled 0.81-0.84 units. The coefficient of organic matter transformation (Pm) increased from initial 59 units without irrigation up to 70-72 units with additional moisturization, which means the increase in conversion of plant residues into organic matter.