Influence of intensive irrigation and cultivation on selected soil properties: Arid southern Namibia

Abstract

The effect of long-term (25 years) intensive irrigation on selected soil properties of the Hardap Irrigation Scheme was determined by comparing soil profiles in irrigated and adjacent non-irrigated areas. The major differences detected between five soil pairs were rubification of the irrigated soils, increase of the mean sand grain size and the sand fraction becoming more poorly sorted, changes in extractable cation composition and an increase in weathering shown by the disappearance of calcite from the clay-size fraction of certain samples. A comparison of electrical conductivity and pH of 470 soil samples measured during a recent soil survey with corresponding values from a 1957 soil survey, signified an improvement in soil salinity. This would seem to indicate that the human impact could be of benefit to soil productivity for the scheme as a whole.

Keywords:

• Calcite
• human impact on soil
• rubification
• salinity level
• weathering processes