An evaluation of the influence of water quality and irrigation management on soil properties of some selected irrigation farms in Kiboko and Makindu

Abstract

Three irrigation farms were studied. Two in Makindu and one in Kiboko. Representative soil sampling sites were selected to represent irrigated and non-irrigated soils. The physical and chemical properties were determined in the laboratory. This was done to study the influence of water quality and management on soil properties. Water samples used for irrigation were analysed to determine their chemical characteristics and their suitability for irrigation. From irrigation point of view, all the waters may be regarded as being unsafe for irrigation particularly on heavy textured soils, unless sufficient drainage is provided and the necessary soil amendments are adopted or salt tolerant crops are grown . .This study has indicated that poor quality irrigation water have little impact on light textured soils. The criteria used to classify soils as well as irrigation waters as having high salinity hazard are not tenable for well drained light textured soils and therefore need modification. Due consideration should be given to soil type, drainage characteristics, topography and irrigation management when judging the suitability of irrigation water. Sufficient drainage should be provided to lower Muhindi farm in order to reduce the groundwater level to below the zone of toot penetration. The waterlogging condition experienced in Makwatta farm is attributable to the dispersed clay colloids brought about by high ESP of the soils. The dispersed colloids moved and blocked the pores through which water flows thus diminishing the hydraulic conductivity of these soils. The pH of these soils is more then 8.5 due to the hydrolysis of adsorbed sodium. Soil amendments would be of doubtful value in correcting the high exchangeable sodium status of the subsoils due to their extremely low permeabilities. Ploughing under of farmyard manure or greenmanuring crops might help improve drainage. The irrigated surface soils of Musengya farm in Makindu are well drained and no appreciable increase in salt accumulation has been experienced despite the use of high salinity water of Makindu river for irrigation. Sufficient drainage should be provided to the fine textured soils of Museng'ya farm in order to reduce the groundwater level to below the root zone and prevent the occurrence of waterlogging condition. Single correlations between irrigation water and soil characteristics were not significant to be of any prediction value suggesting that the soil solution is not in equilibrium with irrigation water.