The impact of different fertilization systems on content, composition, energy intensity of organic matter in chernozem soil

Aim. To determine the regularities of the transformation of quality and quantity composition of humus, its en- ergy intensity at long-term fertilization of soils. Methods. Long-term stationary experiments were conducted on chernozem soils of different granulometric compositions. The analytical work was done in the certifi ed laboratory in accordance with the current normative documents: preliminary treatment of samples for physi- cal and chemical analysis (DSTU ISO 11464); determination of dry substance and humidity by the mass – by the gravimetric method (DSTU ISO 11465). Mass fraction of total carbon was determined by the oxidimetric method (DSTU 4289:2004); humus group composition − by Turin’s method in the modifi cation of Ponomario- va and Plotnikova (DSTU 7828:2015); low heating value of the soil and organic material − by the calorimetric method using В-08-МА set (DSTU 7866:2015); preparations of humic substances were isolated according to DSTU 7606:2014. Results. Long-term fertilization promotes considerable changes in the quality composition of the whole system of humic substances of chernozems of different granulometric compositions. It also has a different impact on the energy accumulation both in the soil and in humic acids (HA). Conclusions. The new formation of HA in typical heavy loamy chernozem with organic and mineral fertilization systems occurs due to the second and third fractions on the background of the decrease in the fi rst and the most mobile fraction of HA. The mobility degree of the whole system of humic substances under the impact of different fertilization systems does not differ from the control considerably; the tendency towards the increase in this index was observed only for the mineral fertilization system. In the organic and mineral fertilization systems, the new formation of HA in typical weak alkali light loamy chernozem occurs due to the fi rst and second fractions. The aggravation of HA structure and the increase in the degree of condensation was registered only for the organic fertilization system. The level of mobility of the whole system of humic substances in this soil is increased compared to the control under the impact of the organic and mineral fertilization systems. A considerable dif- ference in the indices of energy, present in the soil and HA fractions, isolated from this soil, was determined. The maximal amount of energy is in labile forms of HA – in the range of 10.62−15.85 MJ/kg, the smallest amount – in the fractions, tightly connected to the mineral part of the soil (1.47−4.09 MJ/kg). The amount of energy is in direct relationship to the applied agrotechnical means, which is in good agreement with the data on the impact of different fertilization systems on the humic condition of soils.