Impact of Road Construction and Agriculture on Soil Aggregate Stability and Aggregate-Soil Organic Carbon: Ultisols of Derived Savannah

The escalating demands of urbanization and population growth in Southeastern Nigeria have subjected the region’s soil to increasing pressures from both engineering works and agricultural practices. This study investigates the impact of road construction and agriculture on soil aggregate stability indices (ASI) and aggregate soil organic carbon (ASOC). Two locations, Nsukka and Neke Umo, and five land use types: grazing fallow, forest, road grading, and cultivated areas, were examined in Southeastern Nigeria. Employing the transect method, soil samples were collected at 0-15 cm depth to analyze ASI and ASOC. The findings revealed that tillage and engineering activities negatively impacted aggregation, while grazing and forests promoted soil aggregation. Clay flocculation index (0.4-0.87), aggregated silt plus clay (74-415 g kg^-1), water-dispersible clay (36-57 g kg^-1), were strongly determined by particle size distribution (PSD), while variations in meanweight diameter (0.7-1.69 mm), linked to land use and PSD was not consistent. Nevertheless,, ASOC was influenced solely by land use, with grazing land and forests displaying higher SOC storage, compared to road grading and cultivated lands. Intriguingly, cultivation was more damaging than road grading in C storage. These findings provide insights for site-specific approaches to enhance soil structure and carbon storage.