Carbon Sequestration and Aggregation Potentials of Soils Overlying Different Geological Formations in Selected Parts of Anambra State, Nigeria

Background: Soil organic carbon sequestration and aggregation play important roles in maintaining soil fertility, improving soil structural stability and mitigating climate change. Geological formations influence soil physicochemical properties, which may affect carbon storage capacity and aggregate stability. Aim: This study assessed soil carbon stocks and aggregation indices in soils developed over four geological formations in selected areas of Anambra State, Nigeria. Study Design: A comparative field and laboratory investigation was conducted across the Alluvial Plain, Ameki, Imo Shale and Ogwashi-Asaba formations. Methodology: Soil samples from secondary-forest sites were examined at three depth intervals (0–30, 30–60 and 60–90 cm). Particle-size distribution, soil organic carbon, soil carbon stock and aggregation indices were assessed using laboratory methods and statistical analyses. Results: Soil texture ranged from sandy loam in the Alluvial Plain to loamy sand in Ameki and Ogwashi-Asaba and clay loam in Imo Shale. Organic carbon was highest in the Alluvial Plain (0.97 g kg⁻¹) and lowest in Ogwashi-Asaba (0.23 g kg⁻¹). Corresponding carbon stocks were 4.40 and 1.10 t C ha⁻¹, respectively. Mean weight diameter ranged from 0.50 mm in Ameki to 0.64 mm in Imo Shale. Imo Shale recorded the highest state of aggregation (22.08%) and aggregate stability (28.04%), whereas Ogwashi-Asaba recorded the lowest values (12.13% and 14.61%, respectively). Carbon stock declined with increasing depth. Organic carbon was positively correlated with aggregate stability (r = 0.33), while state of aggregation and aggregate stability were strongly correlated (r = 0.80). Conclusion: The findings indicate differences in carbon stocks and aggregation indices among the studied geological formations and support consideration of site-specific soil management practices.