Evaluation the Effects of the Irrigation Water Salinity and Water Stress on Yield Components of Cherry Tomato

The largest share of water consumption in Iran is related to the agricultural sector. Therefore, in order to save water resources, priority is given to reducing irrigation water consumption. On the other hand, reducing of water quality and salinization are the main problems which are commonly found in the areas with limited water resources. One of the most important effects of salinity is the reduction of yield and its inhibitory effects on plant growth and metabolism. Also, increasing salinity can reduce potassium, calcium and magnesium ions. One of the significant points regarding the effects of salinity stress is a significant decrease in the hydraulic conductivity of the roots, which leads to a decrease in the water use efficiency index. According to the food and agriculture organization (FAO), more than 40 percent of Iran's irrigated lands are affected by salinity stress, which is generally found in dry and semi-arid areas. Therefore, studying the combined effect of stress caused by salinity and water stress can be used to provide management solutions for irrigation and crop production.

This study was conducted in greenhouse laboratory at University of Mohaghegh Ardabili, Ardabil, Iran during August to November 2016. In this research, the effects of saline water on cherry tomato yield under water stress conditions were investigated. The applied treatments included irrigation with saline water (in two levels: S1=4ds/m and S2=7ds/m) and water stress (in three levels, irrigation at 40, 50 and 65% field capacity, respectively, I1, I2,I3). The experimental design used in this research was a completely randomized block design with four replications. On the other hand, in order to compare the plant yield under water stress and salinity conditions with non-stress conditions, control treatment with salinity characteristics less than 1ds/m and irrigation without water stress were used in three replications. In this experiment, cherry tomatoes were cultivated in the pots with diameter and height of 26 and 27 centimeters, respectively. The moisture meter (Model: PMS-714) was also used to measure soil moisture and determine the irrigation time. The most important parameters included cherry tomato yield, total evapotranspiration and water use efficiency index. It should be mentioned that analyses of the results were done by MSTATC software (Version: 2.10).

The results of this study showed that the interaction between two factors of water and salinity stress on the parameters was not significant, but the effects of salinity stress on yield, total evapotranspiration and water use efficiency (in two levels: 2% and 5%) are significant. Also, the greatest effect of salinity stress on cherry tomato yield was observed, so that by increasing the amount of irrigation water salinity from 4 to 7 ds/m, the yield was decreased by 27%. Also, the performance in salinity treatments of S1 and S2 decreased by 27.2% and 46.7%, respectively, compared to the controled treatment. Probably the reason for the yield reduction caused by decreasing in plant evapotranspiration and plant growth and metabolism. In addition, water use efficiency index in treatments of S1 and S2 decreased by 3.4% and 22.3%, respectively, compared to the controlled treatment. As it can be seen, the differences in water use efficiency between the control and S1 treatments were not significant. In this study, the average values of Ky (plant response coefficient to salinity and water stresses) were achieved 1.39, which was higher than the value that was reported by FAO for tomato plant under water stress conditions (equal to 1.05). This can be due to the significant effect of saline irrigation water on the yield of the tomato plants. Finally, based on the results of this research, it can be said that although salinity decreased yield significantly at 1% confidence level, in the coming years, with severe water resource constraints and increased costs for its preparation, this yield loss can be economical and feasible.

In this research, the effect of saline water on cherry tomato yield under water stress conditions was investigated. According to the results of this study, with increasing salinity of irrigation water from 4 to 7 ds /m, total evapotranspiration decreased by 10%. On the other hand, due to salinity stress, tomato yield was decreased to 27% in the most salinity levels of irrigation water compared to control treatment; one of the main reasons of which could be the reduction of total evapotranspiration in the growing season. In the end, the important point to note is that although, based on the results of this study, utilization of irrigation saline water decreased the yield, total evapotranspiration and water use efficiency by 27%, 8.9% and 19.2%, respectively compared to the control treatment, but in the near future, by increasing the water production costs and the quantitative reduction of water resources, even use of saline water is economically feasible and justifiable.