Abstract <p>The main physical and chemical characteristics of soils, including their particle-size and mineralogical compositions, were determined as a result of comprehensive radioecological studies on two test plots in the northeast of Stavropol krai within the Chograi-Caspian semi-desert landscape and the Chograi-Ragulinskii landscape of grass steppes. Background concentrations of natural radionuclides (NRs) ⁴⁰K, Th, and U, of technogenic radionuclides ⁹⁰Sr and ¹³⁷Cs, and of their isotopic (Sr, Cs) and non-isotopic (Ca, K) carriers were estimated in the upper (0–20 cm) soil layer. Geo-accumulation indices (<i>I</i>_geo) calculated for heavy metals Cs, Sr, Th, and U, were &lt;0 and indicated the absence of anthropogenic contamination of the soils with these elements, as well as the absence of geochemical anomalies. Based on the vertical distribution data for ⁹⁰Sr and ¹³⁷Cs in the 0–20-cm layer, the diffusion coefficients and convective transport rates were assessed, and the ecological half-life periods for ¹³⁷Cs and ⁹⁰Sr in the 0–10-cm layer were calculated (220 and 77 years, respectively). The activity concentrations of ⁴⁰K, ⁹⁰Sr, and ¹³⁷Cs radionuclides and the mass fractions of their isotopic (Sr and Cs) and non-isotopic (Ca and K) carriers, as well as the mass fractions of HNRs Th and U were estimated in a number of plant species. We calculated the main parameter of the process of biogeochemical migration of the elements in the soil-plant system: the concentration ratio (<i>F</i>_V) for the radionuclides and isotopic (Sr and Cs) and non-isotopic (Ca and K) carriers. The <i>F</i>_V values depended on the plant species and ranged from 0.08 to 0.22 for ¹³⁷Cs and from 0.54 to 1.27 for ⁹⁰Sr. The mean TF values for Th, U, Cs, K, Sr, and Ca could be arranged in the following sequence (<i>n</i> × 10^–2): U (0.005) &lt; Th (0.007) &lt; Cs&#xa0;(0.01) &lt;&lt; K (57) &lt; Ca (76) &lt; Sr (81).</p>