Spatial variability of expansive soil properties at different scales within Kibaha (Tanzania)

Abstract

This paper applies statistical and geostatistical procedures to analyse the spatial distribution of several soil properties and use the contribution of ge ostatistics to plan optimal soil sampling and management schemes in
Kibaha, Tanzania. Particle-size distribution, Atterberg limits and potential swell were analysed. Variogram models for clay content which is strongly correlated to the swell are constructed using the means of the soil properties. The variograms show that the distributions of all variables were not random but spatially-dependent as their estimated variogram values increased with increasing distance. The variograms predicted significantly slower horizontal variation and faster vertical variation of the clay content. The average range values vary between 20 and 30 m in horizontal separation and 1.0 m and 1.5m in depths for particle-size distribution. It implies that if wishing to reduce the need for expensive and intensive sampling, then grid soil sampling will generally have to be performed at interval of less than half the range of spatial dependence of clay content depending on the attribute of interest.