Microorganisms are of great importance in soil fertility improving. Their activity determines accumulation of humus in the soil, mineralization of organic matter and transformation in hard to reach compounds that available for plant form. According to approximate estimates, the soil microorganisms absorb from the air about 100 million tons of nitrogen, phosphorus and potassiuma year, improve plant nutrition. They secrete various physiologically active substances - auxin, gibberellin, vitamins, plant growth and development improves.

In natural conditions, the main source of replenishment of soil nitrogen is biological fixation of molecular nitrogen atmosphere. With intensive technology of cultivation of crops fully recover the cost of nitrogen is only possible by applying fertilizers, biological nitrogen fixation but should not be overlooked. It is known that biologically fixed nitrogen meets the needs of 20-30% of the crop in easily digestible forms of this element.

Soil microorganisms as a mandatory component of agrocenosisand have powerful enzymatic apparatus which makes it possible for microflora to carry out various functions in the soil. Plants are supplied in sufficient quantity of nutrients by mineral and organic fertilizing. However fertilizers can not only enhance but also inhibit the microbiological processes, including biological nitrogen fixation.

Studies were conducted in a stationary experimental fieldof BilaTserkva State Agrarian University during 2009-2013. 5-fields crops rotation is deployed in space and time with 40% saturation of cereals. We studied four basic soil tillage systems and four levels of fertilization.

In our studies, the biological activity of the soil assessment we spent on investigating intensity of decomposition in soil of linen fabric and the number of selected carbon dioxide. It is known that carbon dioxide is the ultimate product of organic matter mineralization and therefore respiration rate (of carbon dioxide) may serve as an indicator of biological activity of the soil.

Under winter wheat the highest biological activity of soil is marked by systematic notillage soil cultivation, the lowest – in a systematic tillage. From 15 September to 15 October and from 15 April to 15 May reduce of weight of linen fabric in the plow layer of black soil was respectively: by the systematic cultivation tillage -16.7 and 15.8% -18.4 bezpolytsevoho systematic and 17.9, differentiated -17.0 and 16.3 and a long shallow -17.1 and 16.4%.

The difference in the amount of carbon dioxide that was isolated during the day, during this period amounted to: the systematic cultivation no tillage - 454.3 and 695.9 mg /m² differentiated - 41.5 and 99.1 and for a long shallow - 52.7 and 142.5 mg/m² for systematic tillage soil cultivation in crop rotation.

The obtained data are consistent with your L.M. Barsukov, K.M. Zabavskoyi, V.R.Williams, I.B. Revut conclusions that in the lower layers, even at very high structuring of soil biological processes take place at a relatively low level.

These layers of soil are biologically less active, especially by flat tillage soil cultivation which means the slower conversion of organic matter and the formation of available nutrients for plants.

Great importance in biological activity of the soil regulating is belonging to cultivation systems. Higher soil biological activity was observed in the rotation by the no tillagesystem than the combined long and shallow. This indicator was the lowest by the tillagesystematic cultivation.

Thus, for the period (from 15 September to 30 October and from 15 April to 15 May) by the control system of cultivation the maximum biological activity of the soil was observed in the 0-10 cm layer, which earned the fertilizer and stubble, and in the 10-20, 20-30 cm layers the biological activity is decreased.

For combined long and shallow cultivation is observed the similar tendency. The highest biological activity of the 0-10 cm soil layer is clamped by the no tillagesystematic cultivation.

Key words: soil tillage, fertilizationlevel, biological activity of the soil, winter wheat.