Evaluation of Koga irrigation water in Mecha district, Amhara Region, as an example of irrigation water quality in Northwestern Ethiopia

Irrigation water quality impacts plant growth, crop production, and public health. Thus, understanding the trends in irrigation water quality is important to manage public health, and optimize crop production. The Koga region in Ethiopia is a developing area where crops are an important food source for a growing population, and irrigation is critical to supply additional food crops and secure food insecurity issues. This study measures physiochemical and biological parameters to assess the suitability of Koga irrigation water for crops intended for human consumption. In March 2022, irrigation water samples were collected and analyzed for physicochemical and biological qualities. Kelley’s ratio, magnesium danger, and sodium absorption ratio were calculated from the data obtained. Results showed that the turbidity (174.33–259.00 NTU), total suspended solids (80.33–175.00 mg/L), total alkalinity (143.33–195.33 mg/L), total hardness (150.67–224.6 mg/L), SO42−(43.96–73.00 mg/L), PO43−(56.27–87.43 mg/L), and BOD5 (63.23–95.40 mg/L) levels surpassed the recommended limit of FAO(35 NTU,50 mg/L,100 mg/L,100–150 mg/L,20 mg/L,3 mg/L and 30 mg/L, respectively). BOD5 levels of the tested water samples exceeded the permissible limit set by the EU (10 mg/L). The coliform and fecal coliform levels in all sampled waters were higher than the zero/100 mL limits of the EU and WHO set for irrigation water. The studied water samples were found to be unsuitable for the cultivation of crops and vegetables since TA, PO4−3, and NO3− levels exceeded the tolerance limit of the crops and vegetables cultivated in the site, while the coliform and BOD5 levels surpassed their tolerable limits. Consequently, it is not recommended to eat crops and vegetables without first properly preparing them. The results showed improper ratio of Mg2+:Ca2+ and Na+:Ca+2, and a magnesium hazard was foreseen. This study showed that the turbidity, total suspended solids, total alkalinity, total hardness, SO42−, PO43−, BOD5, and the coliform levels of the studied irrigation water samples of the Koga irrigation project were not found within the safe limits of FAO, WHO, EU, and irrigation water quality limits of different nations, even though additional samples evaluating seasonal fluctuations are needed to fully assess the water quality.