Effect of long-term application of fertilizers on the humus substances transformation in podzolic soil

The article reflects the results of a study of the regularities of the transformation of humic substances at different levels of structural organization during long-term fertilization against the background of liming of podzolic sandy loamy soil in a field experiment in Western Polissya of Ukraine. It was found that the low content of chemically active organic substances in the humus composition of podzolic soils, caused by the zonal features of humus formation, can be positively corrected by applying fertilizers. Long-term use of organic and mineral fertilizers intensifies the process of new formation of humic acids and the formation of their mobile forms – the ratio of Cha-1 / Cfa-1 is 0.28 in the control without fertilizers and 0.33–0.88 in the variants of fertilization against the background of liming. With an organo-mineral fertilizer system, the most favorable conditions are formed for the humification of organic substances however, the type of humus remained fulvate – the Cha / Cfa ratio is 0.93 in the control variant and 0.41 – against the background of liming. Also, the application of fertilizers had an effect on the redistribution of the polydispersity of humic acids, which was characterized by a decrease in the heterogeneity of the composition of hydrophobic molecular aggregates. In a wide range of 1800 cm-1 to 2500 cm-1, a change in the direction of the line of the integral spectrum of soil humic acids under the application of CaCO3 from left to right was found, which is associated with a change in molecular parameters. Based on the results of chromatographic analysis, it was established that the profiles of the molecular distribution of humic acids podzolic soil correspond to the humus substances class. The first fraction is characterized by the formation of ion associates of larger molecules of polar composition. The recovery of humic acids occurred mainly due to high-molecular structures, which is the most sensitive to the application of fertilizers.