THE ROLE OF MINERAL FERTILIZERS IN THE TRANSFORMATION OF ORGANIC MATTER AND NITRATE NITROGEN IN DARK CHESTNUT SOILS OF THE KARAGANDA REGION

This article presents the results of an investigation into the effects of mineral fertilizers on humus content, its fractional composition, and the dynamics of nitrate nitrogen in agrocenosis of spring wheat of the 'Shortandinskaya 2012' variety under the dry-steppe conditions of the Karaganda region. It was found that no significant changes in humus content occurred during the first year of fertilizer application. The application of nitrogen fertilizer at a rate of 82 kg/ha a.i. resulted in a slight increase in humus content compared to the control. The combined use of ammophos and ammonium sulfate (P82 kg/ha a.i. + N17 mg/kg a.i.) led to a significant increase in humus content in dark chestnut soils. It was found that the concentration of nitrate nitrogen (N-NO₃) increased depending on the combined application of these fertilizers. In the treatment with preliminary phosphorus application at a rate of 82 kg/ha a.i. combined with nitrogen (17 mg/kg a.i.), the level of nitrate nitrogen was higher compared to phosphorus-only treatments without nitrogen supplementation. Under the arid conditions of 2021, enhanced accumulation of N-NO₃ was observed in the upper horizon of the soil profile. The research results indicate that, in the absence of fertilization, there is a decline in both humus and nitrogen content, as well as the degradation of not only mobile nutrient forms but also stable compounds of soil organic matter.