INVESTIGATIONS ON SOIL AND WATER QUALITY AS AFFECTED BY IRRIGATION IN TURKANA DISTRICT, KENYA
Keywords:Irrigation, soil salinisation, water quality, food security, sustainability
Irrigation technology can ensure food security in arid and semi-arid regions. However, its adoption requires efficient systems that ensure sustainable agricultural production. The aim of this study was to investigate soil and water quality as affected by irrigation in the Turkwel Scheme of the semi-arid Turkana District of Kenya. Soil samples were collected spatially and with depth from intensively, moderately and non-irrigated fields and analysed for physical and chemical properties. Irrigation and ground waters were also collected and analysed for quality determination. Phreatic water levels of shallow wells were determined through inspection pits and open shallow wells dug in the scheme. Results of non-irrigated fields indicated a non-saline soil surface with ECe of 1.31 ds/m, which turned saline at depth of 0.20 m with ECe of 5.57 ds/m, indicating salt deposits at this depth. Periodically irrigated fields were strongly saline on the soil surface with ECe of 8.86 ds/m, but decreased to non-saline level of 3.41 ds/m at 0.40 m. However, intensively irrigated fields had low salinity with depth due to frequent leaching of salts. Irrigation and groundwater were of acceptable quality with ECw of 0.13 and 0.33 ds/m, while sodicity hazard was low at SAR of 1.50 and 3.89, respectively. Water table depth had risen from about 1.80 m to 0.70 m from the soil surface between 1982 and 2006, respectively. Soil salinisation in non-irrigated and periodically irrigated fields was therefore attributed to direct phreatic evapotranspiration. Leaching of salts from the root zone, lowering the water table through drainage, and shortening the long fallow period through agronomic practices such as growing drought-resistant vegetable crops can mitigate this land degradation. These would improve food security and living standards of farmers in the scheme.