Soil-Water Relationships and Erosion Dynamics Under Different Vegetation Covers in the Anambra-Imo Gully Erosion Zone

Gully erosion in the Anambra-Imo erosion belt represents one of the most severe land degradation problems in southeastern Nigeria, causing permanent loss of agricultural land and undermining rural infrastructure. Despite the ecological significance of vegetation cover in soil stabilisation, comparative data on soil-water relationships and erosion dynamics across vegetation cover types in this zone remain limited. This study examines soil infiltration rates, erodibility indices, sediment delivery ratios, and runoff coefficients under four vegetation cover types: closed secondary forest, agroforestry plots, fallowed farmland, and bare degraded land across twelve sites in Anambra and Imo States. Rainfall simulation experiments standardised precipitation intensity across cover types. Soil physical and chemical analyses were conducted on surface and subsurface samples. Gully head retreat rates over twelve months were measured from GPS baseline surveys. Closed secondary forest produced the lowest runoff coefficients and highest infiltration rates, reducing erosion rates by 91% relative to bare land. Agroforestry plots delivered 78% erosion reduction. Fallow plots showed intermediate performance, declining significantly when cover density fell below 60%. A threshold relationship was identified between percentage vegetation cover and sediment delivery ratio, suggesting that vegetation cover targets below 70% offer sharply diminishing erosion control. The study recommends minimum 70% vegetation cover targets in erosion-prone catchments and proposes fast-growing agroforestry systems as a practical rehabilitation standard for smallholder land in the Anambra-Imo zone. Keywords: gully erosion, soil-water relations, vegetation cover, Anambra State, erosion dynamics