The use of land form-soil associations in irrigation soil surveys in northern Nigeria

The problems of soil mapping for irrigated agriculture on the savanna landscapes near Kano are discussed. Using data from a detailed soil survey, the possibility of establishing the major variations in soil properties relevant to irrigation by landform-soil association mapping is considered. In the landform classes identified, some soil textural and colour properties have within-class variances somewhat lower than their between-class variances, and moderate interclass correlations. The magnitude of the between-class differences in these properties is great enough to indicate whether the soils can be irrigated successfully and to help determine the irrigation method. Other soil properties including infiltration rate and topsoil available water capacity also differ significantly between landform classes, but their within-class variabdity is still relatively high, indicating the need for further investigations. The variability of most soil chemical properties across the area is not successfully accounted for by landform-soil association mapping. The results suggest that landform-soil association mapping can be a useful means of establishing imgability a feasibility survey level.