Soil erosion assessment at the Udi-Nsukka Cuesta (southeastern Nigeria)

Abstract

Biophysical and participatory research methods were combined to examine factors contributing to soil erosion at field plot, village and regional scale on the sandstone dominated Udi-Nsukka Cuesta in southeastern Nigeria. At field plot scale, the properties of seven pedons were related to soil erodibility. Very high infiltration rates measured with a double ring infiltrometer and permeameter, were not in accordance to reported runoff and soil loss. The effect of groundcover and canopy height was incorporated into rainfall erosivity for plots under cashew, oil palm dominated forest and secondary natural vegetation. Cropping systems and field management practices were compared for different positions along a toposequence traversing the plateau and escarpment of the Udi-Nsukka Cuesta. Soil loss, calculated by a modified version of the universal soil loss equation, was 10 to 100 times higher on escarpment than on plateau plots. Farmers are adapting to the problems of interrill and rill erosion through careful crop selection and rotation, and contour ridging. At the village and regional scale, terrain observations were compared to archival research, historical accounts by villagers and geographic analysis of 1962 aerial photographs (1:40 000). Ravine and gully formations seemed influenced by a combination of infrastructure, geohydrology, topography, vegetation and land use. Both community efforts and state measures to combat erosion tend to be crisis managed, and are concentrated on repairing damage to economically important infrastructures. A conceptual diagram has been developed to show the complex interaction between various geophysical, agroecological, socio-economic and political components influencing soil erosion at farm, village and regional scale. Copyright © 1999 John Wiley & Sons, Ltd.