Quality of land facets as soil mapping units in an area of Northern Nigeria

Abstract

This study examines the quality of land facets as soil mapping units in agricultural soil surveys. This involves sampling the textural and chemical properties of the first two horizons of the land facets in two land systems in a sparsely populated area of northern Nigeria, and assessing whether or not the variances in soil properties between the land facets are significantly greater than the variances that can be observed within each land facet. The size of the variances between the land facets in relation to the variances within the facets (the intraclass correlation), provides the basis for assessing whether or not land facets are homogeneous enough for making predictions about soil and land use potentials. For the top horizons, sand and exchangeable sodium are significantly different between land facets, while clay, pH, exchangeable sodium, potassium and magnesium and cation exchange capacity, total nitrogen and organic carbon have moderate to large intraclass correlations. Only pH and exchangeable magnesium are significantly different between land facets for the second horizons and, except for silt and pH, significantly less than half of the second horizon properties are due to differences between land facets. This suggests that land facets may be useful in evaluating the broad chemical potentials of this sparsely populated environment. Some implications of the results are discussed for soil surveys and agricultural land use planning.