This paper is the result of geological survey engineering.

Objective Taking the typical agricultural area in central Henan Province (Xinmi City) as the study area, this research explores the temporal and spatial variation patterns of soil organic carbon (SOC) in the topsoil (0～20cm) within the region, evaluates the carbon sequestration potential of different soil types, and proposes targeted suggestions for improving carbon sequestration capacity. It aims to provide a scientific basis for enhancing regional soil carbon sequestration function, promoting agricultural green transformation, and implementing the national carbon neutrality strategy.

Methods Based on the measured topsoil data from three periods: 1985 (The Second National Soil Survey), 2006 (Multi-purpose Geochemical Survey), and 2025 (The Third National Soil Survey), Ordinary Kriging Interpolation was used to analyze the spatial distribution and temporal-spatial variation characteristics of soil organic carbon density (SOCD). The carbon sequestration potential of different soil types was estimated by the soil organic carbon saturation value method (combined with clay content fitting, tillage and climate correction). Statistical analysis was used to clarify the effects of soil type and land use pattern on SOC dynamics.

Results The average SOCD in the study area showed a trend of “initial increase followed by subsequent decrease”: It increased from 2.55 kg/m² in 1985 to 3.56 kg/m² in 2006, and then decreased to 3.06 kg/m² in 2025. The average increase amplitude was 1.01 kg/m² during 1985–2006, while the average decrease amplitude was 0.66 kg/m² during 2006–2025. Spatially, the overall distribution presented a distribution pattern of “high in the central part and low in the surrounding areas”. The high-value areas were significantly affected by the distribution of Huanghuai soil and moist cinnamon soil, with obvious differences among different soil types and land use types. The total regional carbon sequestration potential reached 25.47 Tg, among which carbonate cinnamon soil (16.97 Tg) and cinnamon-like soil (5.33 Tg) were the main contributing soil types, accounting for 87.6% in total, while Huanghuai soil had the smallest carbon sequestration potential (0.31 Tg). In 2025, the SOCD of cultivated land was the highest (3.22 kg/m²), and measures such as straw returning and conservation tillage significantly improved its carbon sequestration capacity.

Conclusions Soil type, agricultural management practices (straw returning, fertilization mode), and land use change are the core factors driving the temporal and spatial variation of SOC in the study area. The study area has strong overall carbon sequestration potential. Targeted optimization of farmland management models and protection of superior carbon pools such as carbonate cinnamon soil can effectively enhance the regional carbon sequestration function. The research results can provide a reference for similar agricultural areas in the Huang-Huai-Hai Plain.