Surface Soil Variability of a Map Unit on Niger River Alluvium

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Abstract
Examination of an adequate number of sample points is a prerequisite for valid generalizations in soil surveys. The number of sample points required depends upon a host of factors, including the spatial variability of the properties under investigation. This study examines the spatial variability of textural and chemical soil properties in the surface horizon of two sample areas mapped as Ozugbi series (Typic Humaquepts). From a knowledge of the dispersion characteristics of the soil properties, the number of sample points required to estimate each property at different levels of precision was determined. There were marked contrasts in the variability levels of the soil properties, and, hence, in the number of samples required to estimate each property, between the sample sites and within the map unit as a whole. The pH is the least variable of the properties examined and, hence, needs the smallest number of samples for estimation.