Evaluation of suitability of Notwane river water for vegetable irrigation and its impact on the soils and drip irrigation facilities: a case study of Kgatleng district, Botswana

The study was carried out to assess the suitability of Notwane river water for crop irrigation and its impact on irrigated soils and drip irrigation system. Water sampled from four farmer abstraction points along the river was analyzed for the physio-chemical parameters using standard methods for water and wastewater. Irrigated soil was sampled from the four farms and analyzed using standard soil analysis methods. It was observed that water pH, Total Suspended Solids and E.Coli were not within the recommended irrigation water quality guidelines by Botswana government. Notwane river water indicated slight pollution giving Comprehensive Pollution Index (CPI) of 0.69. Comparison of analyzed soil parameters with FAO standards indicated that soil pH in 50% of sampled locations was above the FAO recommended pH of 6.5. The computation of Langelier and Ryznar stability indices (LSI and RSI) indicated intolerable corrosion of irrigation pipes by river water at all sampled locations with LSI and RSI values in range -4.31 to -2.11 and 12.82 to 15.01, respectively. Based on the analyzed physio-chemical parameters, Notwane river water is suitable for vegetable irrigation except for the pH, which has to be adjusted to a stable condition by adding lime and/or sulphuric to prevent nutritional imbalances and potential for intolerable corrosion of piped water distribution systems. To prevent the severe pollution of E.Coli in river water the government of Botswana must set a regulation control that indiscriminate water use along the river. The use of filters is recommended to control TSS which might up blocking drip system.