Appraisal of ground water quality and its impact on irrigation soils in Khartoum State, Sudan

A study was undertaken to appraise the quality and impact of well waters on irrigated soils of fifty farms widely spread in Khartoum State, Sudan. Water quality indicators and pertinent soil properties were measured by standard procedures. The determinations were electrical conductivity of water (ECW) and soil saturation extracts (ECe) and soluble Na**+, K**+, Ca**+ Mg**++, C1, RC03 and SO4. Sodium adsorption ratio (SAR), residual sodium carbonate (RSC), theoretical pH (pHc) and Langeleirs saturation index (LSI) were computed. A questionnaire including pertinent well and farm data and information was filled. ECw ranged between 0.4 to 4.8 dS/m. According to the United States Salinity Laboratory (USSL) classification system, 30% of the water samples lied within the medium salinity class, 62% lied within the high salinity class and 8% within the very high salinity class. In agreement with USSL, highly significant linear correlations between ECw and total salt concentration of water expressed in mmole**+/l or mg/l with 99% accountability were found. Ninety-eight percent of the water samples were non-sodic. Only one water sample gave a SAR value equal to 19.1 and the remaining waters had SAR ranging between 1.1 and 9.4. RSC was negative for all water samples with the exception of two samples (4%) that gave RSC values 0.6 and thus within the safe level. In general, LSI data agreed with RSC data. The well waters were predominantly Ca-N/SO4=C1 waters. The results showed that 70% of the top layer of the irrigated soil had ECe values that ranged between 0 and 2 dS/m, 14 ranged between 2 and 4 dS/m and 16% had ECe values greater than 4dS/m.Comparison between irrigated and non-irrigated top soil samples indicated that thirty-four (68%) soil samples were leached, thirteen (26%) management. were salinized and three (6%) were not affected by irrigation with ground water. The soils, which were salinized, had the following texture classes: four clays, two clay loams, five sandy clay loams, one sandy clay and one sandy loam. The leached soils also included different types of textures, which indicates that salinization resulted from poor soil and water management