Potable underground water supplies, which are currently the largest source of water for irrigation, are limited in our country, so it would be reasonable to think about alternative sources of water for irrigation in the future, such as treated wastewater (TWW). In an experiment conducted from May to September 2020 on 30 lysimeters in the Central wastewater treatment plant of Ajdovščina, we wanted to find out how irrigation with TWW and TWW to which modern contaminants have been added (SWW) affects the yield and quality parameters of tomato fruits. The plants in the control treatment were irrigated with potable water (PW). Lysimeters that were not planted with plants were also included in the experiment in order to determine the influence of the plants present on the parameters of the leachate (pH and electroconductivity (EC)). Fruit harvesting took place from the beginning of August to mid-September. At each harvest date, the number of fruits per plant was counted and their weight were weighed. Fruit sampling for the analysis of quality parameters took place in three periods (August 4, August 28 and September 11, 2020), as we wanted to investigate whether prolonged exposure of the plants to modern pollutants affects the content of sugars, organic acids, vitamin C and carotenoids. Results showed that the use of TWW, with or without the addition of modern contaminants, had no significant effect on yield. Irrigation with TWW and SWW had no significant effect on sugar, vitamin C and carotenoids content compared to the control plants. However, the content of malic acid was higher in the fruit of the plants irrigated with TWW and SWW compared to the control plants, which was irrigated with PW. The results of pH and EC measurements in the leachate showed that irrigation with TWW and SWW did not affect the pH and EC of the leachate from the lysimeters compared to the control treatment. However, a higher EC of the leachate from the TWW and SWW treatments without plants was observed compared to the lysimeters of the same treatments with plants.
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