In the soil cover of the forest-steppe zone, typical chernozems, which occupy almost 50% of the total area of arable lands that are insufficiently fertilized with organics and minerals, prevail. Our task was to investigate the potassium content in these soils in order to gain insight into its reserves and availability for agricultural plants. For this purpose, soils of this type of different granulometric texture were investigated. The content of the fine-dispersed fraction of typical chernozems, total potassium in this fraction and in the soil as a whole is determined. Indicators on the genetic horizons were researched there. The content of hydromicaceous minerals as the most available potassium reserves of plants nutrition is shown. The reserves of potassium (after Gorbunov) in one meter-deep layer of investigated soils are calculated. All investigated soils have the same specificity of the reserves distribution in the horizons due to the common genesis processes and the same parent materials. The illuvium horizon of podzolized chernozem entraps a certain part of silt and potassium that is explained by the specifics of the formation of this horizon. Near reserve of chernozem soils contains less than 50% of potassium from the general reserve that suggests the potassium depletion of chernozems.