Compilation of a soil map for Nigeria: a nation-wide soil resource and land form inventory

Abstract

This paper presents the results of a nation-wide soil and land form inventory of Nigeria. The data compilation was conducted in the framework of two projects with the objective to calculate agricultural production potential under different input levels and assess the water erosion hazard. The information on spatial distribution of soil and land form attributes comprises: soil unit, texture, phase, soil depth, drainage, soil erodibility, altitude, slope gradient, slope length and aspect. Soil information was obtained from existing national and regional soil surveys while the land form characteristics were derived from a Digital Elevation Model (DEM). The results of the inventory are presented in (rasterized) maps accompanied by attribute tables. The information is of diverse reliability. Especially in the Mid-Western and Northern Central part of Nigeria, the soil information depends largely on reconnaissance surveys only. The algorithm that was applied on the DEM to derive the slopes produced unexpected and probably inaccurate results. The final slope map combined information sources from the DEM, Soil Map of the World and the FDALR study. It is recommended that more soil information is collected in the poorly described areas and that an improvement of the slope map be realised through research on slope algorithms or by elaborating large scale altitude maps with contour lines.

Nigeria Journal of Soil Research Vol. 6 2005: 71-84