Estimation of Soil Carbon Balance Based on СО<sub>2</sub> Emission Determination

The increased interest nowadays in quantitative assessment of soil respiration is largely due to studies of the role of various terrestrial ecosystems in changing the concentration of the most important greenhouse gas, CO2, in the atmosphere. The review considers methodological aspects of determining the actual CO2 emission from soils using chamber and absorption methods, as well as the use of the obtained data to assess the carbon balance in soils. Successful development of this topic will allow to promptly get an answer to the main question of this pressing environmental issue: what is the soil of this or that ecosystem for atmospheric CO2 – a net source or a net sink? The article analyzes the results of works devoted to comparative determination of CO2 emission from soils by these methods. It is shown that the widespread opinion about obtaining underreported data by absorption method is often based on studies in which the basic principles of the method were violated. It is concluded that it is necessary to carry out in-depth comparative studies on determination of average daily indicators of CO2 emission from soil by chamber and absorption methods. It is recognized that, regardless of the method, the main problem in using CO2 production data to estimate soil C balance is the adequate partitioning of total respiration into heterotrophic and autotrophic components, the ratio between which varies widely depending on soil and vegetation conditions. Due to imperfection and labor intensity of existing methods, this division can cause significant errors in determining the annual mineralization of soil organic matter. To reduce them, the approach to determination of mineralization losses of CO2 in bare fallow soils is considered. It is natural for soils of agrocenoses, but as a methodological technique can probably be used in natural grass ecosystems as well. Reduction of errors can be ensured due to the fact that differences in actual mineralization of organic matter in bare fallow and plant-occupied soils are several times less than changes in the ratio between heterotrophic and autotrophic components of soil respiration in different biogeocenoses.