Dilmurat Yerzhan

Increasing aridity, strong interannual variability in water availability, and limited crop diversification threaten soil organic matter in the chernozems of Northern Kazakhstan, where continuous spring wheat cultivation remains widespread. We assessed seasonal and interannual soil organic carbon (SOC) dynamics in haplic (ordinary) chernozem under conventional tillage (CT) and no-till (NT) during the completed 2023–2025 field seasons at the Karabalyk Agricultural Experimental Station. CT and NT were evaluated without fertilizer and with N30P20 fertilization; bare fallow served as an uncropped reference. In the 0–20 cm layer, SOC concentration, total nitrogen, humus, microbial biomass carbon (Cmic), soil temperature, moisture, and CO₂ flux were evaluated; humic acid carbon (HA-C) and fulvic acid carbon (FA-C) were directly measured only in 2024–2025. Mean seasonal SOC concentration was significantly affected by Year (F = 4.622, p = 0.020, partial η² = 0.278) and Fertilization (F = 4.301, p = 0.049, partial η² = 0.152), whereas the overall Tillage effect was not statistically significant (F = 0.417, p = 0.525, partial η² = 0.017), and the Year × Tillage interaction was also nonsignificant (p = 0.909). HA-C and FA-C varied markedly between seasons and years without a consistent NT advantage, while the SOC–Cmic relationship showed a strong positive trend that did not reach the predefined significance threshold (r = 0.809, R² = 0.654, p = 0.051). These results emphasize dominant interannual variability and the need to distinguish descriptive tillage differences from statistically supported management effects. These findings are relevant to sustainable soil management and the development of climate-resilient dryland wheat production under increasing climatic variability in Northern Kazakhstan. The present study evaluates SOC concentration rather than SOC stock or sequestration.

Introduction. Sustainable agriculture in the grain-producing regions of Kazakhstan requires a transition from generalized technological solutions to agroecologically differentiated land resource management. In this context, verification of productivity zones identified by NDVI is of particular importance, since remote sensing indices reflect the spatial heterogeneity of crops but do not always explain its soil-landscape and biological causes. Materials and methods. The aim of the study was to perform agroecological verification of NDVI-based productivity zones through the analysis of microrelief, soil agrochemical status, and phenological indicators of agricultural crops. The study was conducted in 2024–2025 on the territory of Olzha-Sadchikovskoye LLP, Kostanay District, Kostanay Region, covering an area of 1,500 ha, including fields No. 18, No. 33, No. 67–71, and No. 90. The study used soil-landscape survey materials, SRTM data, NDVI images, satellite images with a resolution of 2.44–30 m, results of agrochemical analysis of the 0–20 cm soil layer, and field phenological records. Results and discussion. A three-level verification scheme was proposed: the remote sensing level — NDVI; the soil-landscape level — microrelief and agrochemical indicators; and the biological level — plant density and plant height. It was established that stable productivity zones are associated with relief, moisture availability, particle-size composition, and nutrient supply. The stable area of the zones was 72% in field No. 67–71, 43% in field No. 18, and 58% in field No. 90. The content of available potassium increased from slopes to depressions, from 650 to 950 mg/kg. Conclusion. NDVI zones should be considered as a diagnostic layer requiring soil-agroecological and biological verification to substantiate differentiated crop management.

Cropping systems and agronomic practices play a critical role in regulating soil organic matter dynamics and carbon dioxide (CO₂) emissions, which are key components of the global carbon cycle and climate change mitigation. However, the combined effects of tillage practices and seasonal climatic variability on CO₂ fluxes in chernozem soils (chernozems, WRB classification; highly fertile, humus-rich soils typical of steppe regions) of Northern Kazakhstan remain insufficiently understood. The aim of this study was to quantify soil CO₂ emissions under conventional tillage, no-till, and bare fallow systems during spring wheat cultivation on ordinary chernozems. Field experiments were conducted between 2023 and 2025 in the Kostanay Region (Kazakhstan). Soil CO₂ fluxes were measured using a chamber-based method, while soil temperature, moisture, and microbial community structure were monitored simultaneously. The results revealed pronounced seasonal and interannual variability in CO₂ emissions, ranging from 2 to 27 g CO₂·m⁻²·day⁻¹. Conventional tillage resulted in higher peak emissions due to increased soil aeration and accelerated organic matter mineralization, whereas no-till systems exhibited a more stable seasonal pattern and lower temperature sensitivity of soil respiration (Q₁₀ = 2.40 for no-till and 3.25 for conventional tillage). The application of machine learning techniques (Random Forest) significantly improved the prediction accuracy of CO₂ fluxes (R² = 0.67; RMSE = 3.37 g CO₂·m⁻²·day⁻¹) compared to linear models. These findings provide a scientific basis for the development of climate-smart agricultural practices aimed at improving carbon management in semi-arid steppe agroecosystems.