Influence of irrigation water quality on soil salinization in semi-arid areas: a case study of Makutopora, Dodoma-Tanzania

Abstract

This research was carried out in Dodoma, at Makutopora Agricultural Research Institute. The main objective was to determine the influence of irrigation water on soil salinization in semi-arid areas. A total of 80 representative soil samples were randomly collected from study area. Two water samples were also collected from the study area. The samples were treated and analyzed for physical and chemical related indices. The results are grouped into general quality parameters, which included salinity and salt inducing cations and anions. The findings indicated that the mean pH was 7.53 while the mean EC value was 944.5 μS/cm. The mean cations in the water were 3.97, 4.32, 2.57, and 11.39 meq/l for Ca2+, Mg2+, K+, and Na+, respectively. The Sodium Adsorption Ratio (SAR) was 5.60. The mean carbonates concentration detected in the irrigation water was 9.05 meq/l, while the mean chloride and sulfide were 17.20 and 3.6 meq/l, respectively. Soil samples were grouped into three major groups namely non-irrigated, half irrigated, and full irrigated soils. For the non-irrigated, half irrigated, and full irrigated soils: the mean pH in the soil was 6.59, 6.89 and 7.04, respectively; the mean ECe were 94.35, 338.5, and 344.72, mS/cm, respectively; SAR was 0.76, 2.64, and 4.82, respectively; exchangeable cations and anions as shown in Table 4, 6 and 8. The results reveal that water may have the potential to be hazardous to the soil as well as to the crop grown because most parameters were above safe limits. The linear regression model showed high correlation of soil salinity with exchangeable bases with R2 =0.776 and significant at p≤0.04 for non-irrigated soil, R2=0.627 at p≤0.001 for half irrigated soil, and R2=0.597 at p≤0.003 for full irrigated soil. For all soil samples the linear regression model shows strong relationships that exist between the soil salinity and exchangeable bases present in the soil. It is recommended that adequate drainage with emphasis on surface drainage should be provided and salt and sodium build up should be monitored regularly