Assessment of seasonal variations in groundwater quality and its suitability for agricultural use in Keffi, Nigeria

Abstract Groundwater within the Basement Complex terrain of Keffi and its environs were assessed for its quality and suitability for agriculture. A total of about sixty-three groundwater samples were collected during wet and dry season, where physical and chemical parameters were measured. Results obtained show that values of analyzed parameters are within WHO permissible limit, except NO3−. Groundwater in the study area is of good to excellent quality. Major cation constituents during both seasons occur in order Ca2+ > Na+ > Mg2+ > K+. In the wet season, major anions in the groundwater occur in the order NO3− > HCO3− > Cl− > SO42−, while in the dry season it is NO3− > Cl− > SO42− > HCO3−. During weathering processes, dissolution may be responsible for the release of these major ions into the groundwater system owing to the rock-water interaction. Also, groundwater in the study area is suitable for agriculture based on the indices: total hardness, residual sodium carbonate, percent sodium, sodium absorption ratio, magnesium hazard and permeability index. Correlation suggests that anthropogenic sources contribute the excess NO3− in the groundwater through the application of fertilizer and pesticide, improper disposal of refuse and even indiscriminate open defecation over time. Majority of the groundwater samples analyzed for both season were classified as; ‘very good to good’ and ‘good to permissible’, using the Wilcox Plot. Similarly, the plot of sodium hazard against salinity hazard has classified the groundwater samples analyzed as ‘good’.