Introduction: The sharp decline of surface freshwater and groundwater resources in recent decades in most parts of the country are the most important issues of Iran today. One of the serious problems of the plains of Iran is the lowering of the water level of the wells the drying of the Qanats and the salinization of their water followed by the salinization of valuable soil of agricultural lands especially in dry and arid areas. Therefore appropriate strategies for exploiting unconventional water resources such as saline groundwater and seawater and agricultural drains can help reduce the negative effects of depletion of water resources. In this study one of the ways to exploit saline water resources was investigated. Due to its location in an arid and semi-arid region Iran has a high potential in the solar energy. Desalination of saline water by evaporation and condensation with the help of solar energy for the use of plants (distillation irrigation) is one of the simplest methods to produce fresh water that can be used in agriculture.

Materials and Methods: In this study by implementing plastic and polycarbonate structures the effect of material and size of different distillation surfaces in the distillation irrigation method on the yield and water use efficiency of tomato plants were investigated. This research was conducted in the research farm of Shahrekord University and from June to October 2016. Experiment in 7 treatments and 4 replications as a factorial experiment in a completely randomized design with two types of distillation surface materials including transparent plastic plate (P) and polycarbonate plate (PC) with two transparent walls and three external surface sizes (0.48 72 0. and 0.96 square meters) were done. The salt water used was also supplied from the salt water spring of Ardal city of Chaharmahal and Bakhtiari province. To compare the results a treatment with subsurface drip irrigation (fresh water irrigation) was also considered as a control treatment. In this experiment the parameters of fruit number fruit weight shoot weight and dryness fresh water volume produced in each treatment ion leakage rate leaf surface temperature and water use efficiency were measured.

Results: The results showed that P3 treatment (plastic plate with external surface of 0.96 square meters) had the highest amount of fresh water production during the experiment (21 liters). In contrast PC3 treatment (polycarbonate plate with external surface of 0.48 square meters) produced the lowest freshwater (16.5 liters). Transparency of the plastic treatments and consequently more light passing into the structure than polycarbonate treatments can be the reason for the difference in fresh water production. The maximum light transmission through the transparent plastic and double-walled polycarbonate is about 91 and 80% respectively.

Due to the production of the highest amount of fresh water in P3 treatment the highest number of fruits heavier fruits and heavier and drier plants were also observed in this treatment. In contrast the lowest amount of fresh and dry plants in PC3 treatment and the lowest number and weight of fruit were observed in PC3 P1 and P2 treatments which did not show a significant difference. The lowest amount of ion leakage and leaf surface temperature were observed in the control treatment which indicates that this treatment was not under water stress.

Among other treatments the lowest amount of ion leakage was observed in P3 treatment which produced the highest amount of fresh water. The highest amount of ion leakage and leaf surface temperature were also observed in PC3 treatment this treatment had the lowest amount of sweet water production. Therefore it can be said that this treatment was under water stress. The lowest amount of fruit and plant material production in this treatment is also shows this issue. The highest water use efficiency in terms of fresh weight of fruit was about 11 g/l in P3 treatment which is not statistically significant with PC1 and PC2 treatments. The lowest value is related to PC3 treatment with a value of about 4 g/l which is not significantly different from P2 treatment. The control treatment had the lowest water use efficiency compare than the other treatments because it receives water based on its water requirement and part of the water is also lost by gravity. The P3 treatment with transparent plastic produces more fresh water and its water use efficiency is higher than the other treatments.