Spatial variability of two selected soil properties in a semi- arid subcatchment of the Lower Great Fish River

Abstract

The variability of the soluble salt content and the textural composition of the soil were investigated in a 28-ha sub-catchment of the Ecca River, a tributary of the Great Fish River. The frequency distribution of the soluble salts in the 0–300 mm depth layer, is log-normal, with the untransformed data having a coefficient of variation (CV) of 60%. The silt plus clay content of the soils also follows a lognormal distribution and has a CV that ranges between 32% (left slope) and 41% (right slope). No spatial structure is evident in the properties of the soil samples collected in the traverses parallel to the river. However, on both sides of the river channel, the mean salt content of the top-slope positions is higher than that of the foot-slope positions. A Student's t test shows that some of these differences are statistically significant. On the left slope no differences can be detected in the silt plus clay content of the various slope positions, but on the right slope the percentage of fine material at the foot-slope is significantly higher than at the top-slope. Indications are that these trends in the spatial structure of the two soil properties might be related not only to the type of, but also to the dip of the geological strata.