Evaluation of the effect of different wastewater qualities on some biochemical and morphological traits of tomato plant under deficit irrigation

With the increase of population, migration to cities and expansion of urbanization, improvement of living standards, and expansion of industries have caused a large volume of sewage to be produced in limited areas that the environment can not be refined. However, this high volume of wastewater can be considered a source of water, materials, and energy. Today, many countries make optimal use of water resources and advance their national development programs by recycling them. The use of wastewater in agriculture should not be based on a general rule. Still, it should be based on water, soil, and environment characteristics and establish a proportion between the quality of the wastewater and the type of wastewater application according to economic issues. This subject requires access to executable standards, instructions, and criteria for each of the different sections to be used to observe environmental standards. Of course, wastewater as a stable water source in irrigation of agricultural products and obedience to ecological considerations should be considered part of sound management for the water crisis.

A factorial experiment was conducted in a complete randomized design with 15 treatments and four replications in the research greenhouse of the Faculty of Agriculture, Ferdowsi University of Mashhad. For this experiment, 60 pots, 6 kg containing sandy loam soil were used. Treatments include urban water (W), treated wastewater (TWS), untreated wastewater (WS), combined urban water and treated wastewater ratio of 50:50 (W + TWS), and combined urban water and untreated wastewater (W + WS) (50:50) as irrigation water and three levels of irrigation were 100, 70 and 40% of the plant's water requirement. First, treated wastewater samples, untreated wastewater, and urban water were taken to the laboratory for water quality analysis. The seedlings were transferred to the desired pots in the three or four-leaf stage. After 150 days, the plants were harvested from the pools, and traits such as leaf number, leaf area, chlorophyll a, chlorophyll b, carotenoids, and proline were measured.

According to the analysis of variance tables, the results show that the simple effect of water quality treatment on the leaf number, leaf area, chlorophyll a and b at the level of one percent probability have a significant difference, but there was no significant difference in proline and carotenoid traits. In simple effect of deficit irrigation treatment, all measured characteristics have a considerable difference at the level of one percent probability. But, in the interaction effect of water quality and deficit irrigation, leaf number, leaf area, chlorophyll a and b, and carotenoids trait were significant at the level of one percent probability, and proline trait was not significantly different. Therefore, due to the interaction of water quality and deficit irrigation treatments, the most leaf number related to the treatment of 100% of the plant's water requirement with untreated wastewater, and the least leaf number belongs to the treatment of 40% of the plant's water requirement with urban water. In the leaf area, the most amount is related to 100% of the plant's water requirement with untreated wastewater. The least amount is related to 40% of the plant's water requirement with urban water. In chlorophyll-a trait, the most amount of chlorophyll a is associated with the treatment of 100% of the plant's water requirement with untreated wastewater. The least amount of chlorophyll is associated with 100% of the plant's water requirement with treated wastewater. In chlorophyll b, the most amount is related to the interaction treatment of 100% of the plant's water requirement, and the combination of urban water and untreated wastewater in the ratio of 50:50 and the least number is related to the treatment of 100% of the plant's water requirement with treated wastewater. Also, in the carotenoid trait, most carotenoids were related to 100% of the plant's water requirement with untreated sewage. The least amount of carotenoid was linked to 40% of the plant's water requirement with untreated wastewater.

According to the results, it can be concluded that the leaf number, leaf area, chlorophyll a, and chlorophyll b in the treatment of urban water with untreated wastewater was more than the control, and the quality of irrigation water on proline was not significantly different. Also, it is concluded that the plant's natural response to drought stress depends on the amount of water and can be short-term or long-term physiological responses. Thus, the lack of access of tomato plants to enough water reduces physiological traits such as leaf number, leaf area, and photochemical traits such as chlorophyll a, chlorophyll b, and carotenoids. But deficit irrigation increases the amount of proline, and with the drought stress intensifies, the number of proline increases. Thus, in conditions of deficit irrigation, the plant reduces its osmotic potential to absorb more water by accumulating potential osmotic regulators such as proline and soluble carbohydrates in the leaf.