Methodological aspects of determining the processes of organic matter mineralization↔synthesis in croplands

Aim. To determine the peculiarities of N[2]O and CO[2] soil emissions under different systems of crop fertilization. Methods. Field experiment, gas chromatography. Results. The data obtained during the permanent fi eld experiment on leached chernozem with crop rotation including potatoes, spring barley, peas and winter wheat have shown that both absolute (N[2]O) and specifi c (relative to carbon losses in the form of СО[2] ) losses of nitrogen depend on crop fertilization system. The introduction of raw organic material to the soil in the form of cattle manure or lupine (green manure) has led to the increased CO[2] emission levels. However, specifi c nitrogen losses in the form of N[2]O (g N-N[2]O/kg C-CO[2] ) have remained at the control level. The application of mineral fertilizers (under the absence of raw organic material) have triggered N[2]O emissions and more intense production of CO[2] (up to 67 % in the variant with the highest dose of mineral fertilizers (N[120]P[120]K[120] kg/ha of active ingredient), which can be caused by the mineralization of humus compounds. In organo-mineral fertilization system the specifi c losses of nitrous oxide have not exceeded the control and fallow. Based on the obtained results the authors propose the method of determining the “mineralization-synthesis” indices of organic matter in agricultural soils for estimation of the orientation of biological processes under different crop growing conditions. Conclusions. Systemic application of mineral fertilizers without introduction of raw organic material leads to the misbalance of mineralization and synthesis processes in soils. Under such conditions the mineralization of organic matter is prevailing. The use of organic and organo-mineral fertilizers has balanced these processes in the soil. The proposed methodological approach for determination of mineralization-synthesis indices is based on the emission ratio of g N-N[2]O/kg C-СО[2] compared to the reference values and can provide an objective view of the tendency of mineralization (negative ratio values) and synthesis (positive ratio values) processes in the soils. It provides grounds to the decision-making principles of agricultural crops fertilization or introduction of certain agronomic techniques.