An assessment of the influence of slope segments on soil properties in the Mua Hills, Machakos County

Abstract

As a factor that is involved in soil formation, topography mediates the interaction of soil and geomorphological processes on a hillslope and this essentially influences the soil properties in a location. Soil properties of depth and texture are not randomly distributed and in a local setting where soil forming factors are fairly constant, soils have a close relationship with topography and geomorphic setting. The objective of this study was to investigate the spatial distribution of soil properties of depth and texture in relation to slope position. Soil depth influences soil moisture storage and texture is a key soil property that influences water drainage and susceptibility to erosion. The soil depth as a measure of erosive geomorphic process was thinnest at 15cm on the transportational slope and thickest at 244cm on the toeslope. Clay soil composition was at an average of 4% along the slope with the highest clay composition being recorded on the river channel at 8% while silt soil composition was at an average of 30% along the slope, with the highest concentration of 47% being recorded on the river channel. The river was a seasonal channel and at the time of this field work, it was dry. Sand soil composition was generally high along the hillslope with an average of 58% along the slope, with the backslope having the largest sand content at 77%. The highest concentration of gravel was on the transportational unit at 45%. Stratified sampling technique was applied to identify the seven geomorphic units used in the study. From the seven identified geomorphic units, purposive sampling method was consequently applied to choose the twenty sampling points which were deemed to be inclusive of the study population. The study findings indicated that the soil properties of depth and texture had been influenced by the slope position in the Mua Hills. The thinnest soils were in the middle steep slopes, which also recorded the coarsest soil textures. To this, it is recommended that when soil property variations are matched to the slope segment on the hill, then it is possible to conduct area specific land management on similar landscapes.