Effect of irrigation on soil salinity profiles along the Lower Vaal River, South Africa

Abstract

The impact of long-term irrigation on semi-arid soils along the Lower Vaal River in central South Africa was assessed. Irri gated sandy and clayey soils representative of relatively homogeneous agro-ecosystems were sampled at 200 mm intervals to a depth of 2 m wherever possible. To serve as a reference, adjacent virgin soils were sampled wherever possible. All the samples were analysed for common salinity indicators. Soils irrigated for more than 20 years with water varying in electrical conductivity (EC) from 52 to 74 mS·m-1 and sodium adsorption ration (SAR) of < 5 reacted differently. Salts were generally less and more evenly distributed in the virgin profiles than in their irrigated equivalents. In the irrigated clayey soil at Spitskop the salt content increased with depth. In the irrigated sandy soil at Vaalharts maximum salt accumulation occurred above the water table, whereas in the centre pivot irrigated sandy soil at Wildeklawer it occurred at 400 to 800 mm depth.

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