Study of Copper Phytotoxicity on Maize Plants (Zea mays L.) Irrigated by Water Treated with Copper Sulfate as Algaecide

The phytotoxicity of Copper Sulfate used as algaecide in irrigation water on maize plants tissues (Zea mays L. ) and its accumulation in soil has been studied, using two irrigation modes Basin Irrigation and Sprinkler Irrigation. Disinfected seeds were inoculated in plastic columns containing clay loam soil. Experimental plants in columns were irrigated with water treated by copper sulfate (CuSO4, 1ppm), and control crops by tap water. The morphological effect of copper (Cu) on the growth of maize plants was followed weekly during two months in comparison with control plants. Experimental plants showed a decrease of leaves surfaces by 8 %, without any foliar toxicity symptoms or significant effect on shoot height. However, the use of copper sulfate in irrigation water have decreased the total dry mass by a value greater than 11 %, which is closer to 10 %, This latest occurs when the element is at the critical toxic concentration in plant tissues. The bioaccumulation of copper in maize tissues (roots, shoots, and leaves) was measured in both irrigation modes. Average total masses of Cu in plants irrigated by basin and sprinklers modes showed an increase of Cu masses by 35 % and 46 %, respectively, compared to their corresponding control plants. In basin, copper bioaccumulation has occurred in root tissues through roots uptake, whereas by sprinkler method, the bioaccumulation has occurred in roots and leaves through roots uptake and leaves diffusion. Furthermore, the deposition of copper on leaves and shoots by sprinkler irrigation reduces greater than 8 % the growth of plants in comparison with basin irrigation mode, and thus, increased further the phytotoxicity rate. The vertical distribution of total copper in soils irrigated by copper treated water was also examined. At the end of irrigation period (two months), retention profiles showed that the concentrations of retained copper in the upper 0.2 cm of the soil are 28.23 ppm and 22.35 ppm when basin and sprinkler irrigation are applied respectively, and then decrease for the following depths. Therefore, this study has confirmed that the use of copper sulfate in irrigation water leads to copper bioaccumulation in plant tissues and with time, to its accumulation in soil. Consequently, this entails an increase of phytotoxicity rate. It proved as well the impact of irrigation modes on copper bioaccumulation rate and uptake pathways. Finally, this document showed the need to look for another alternative of copper sulfate as algaecide.