The dynamics of organic matter, nitrogen status, and biological activity in soils in southern Kazakhstan under various land-use systems were studied. A key feature of the research is the comprehensive comparison of humus status, nitrogen state, and biological activity of virgin and arable dark Kastanozem, Gleyic Calcisol, and Haplic Calcisol, as well as identification of their correlation with signs of functional depletion of organic component. The assessment was conducted using set of agrochemical and biological methods, including determination of humus content, available nitrogen forms, C/N ratio, microbial population, and enzymatic activity. It has been determined that the highest humus content is typical for dark chestnut soils under natural vegetation, while plowing of them is accompanied by decrease in humus content due to increased mineralization processes. Gleyic Calcisol - are characterized by more stable humus state, in some cases with increased organic matter content under arable conditions. Minimum humus values were found in Haplic Calcisol, due to arid conditions and limited supply of organic residues. It is shown that arable soils are characterized by a decreased C/N ratio and increased rates of organic matter transformation. Soil biological activity is linked to mineralization processes, as confirmed by microbial population dynamics and enzymatic activity. Additional assessment using digital tools reveals signs of functional depletion of organic component in agrocenoses. The obtained results indicate the need to consider biological indicators when assessing soil conditions and developing sustainable land management systems in arid climates.