کارایی ‌مصرف آب و عملکرد گیاه فلفل قلمی در روش شیرین سازی آب شور به روش میعان با نور خورشید (آبیاری تقطیری)

Introduction: Freshwater resources are fundamental for agriculture and food production. The increasing demands for water and climate changes cause shortage of freshwater on the planet. The water shortage can also limit the agricultural production, which can endanger the human food security. Due to the restriction of freshwater resources in the recent decades, many researchers have focused on the use of new methods for sweetening saline water. The sweetening saline water needs energy and this causes restriction use of these processes. Use of renewable energy sources is one of the best solutions for this problem. Solar energy is an environmentally responsible method of generating power, and also makes financially sense. In addition to being renewable, solar energy is typically labeled as a green source of energy due to the lack of harmful environmental side effects associated with its use. Iran has a high solar energy potential, because it is located in mid-latitude and also arid region of the earth. Sweetening saline water by using solar energy is one of the methods in which saline water first evaporates and then converts to fresh water by condensation. It is called condensation irrigation when it is used for irrigation purposes. Condensation Irrigation (CI) is a combined system for solar desalination and irrigation. The CI system presented in this research uses solar thermal energy to evaporate saline water. At the first, the saline water converts to vapor by solar energy and then, the vapor is being cooled and precipitates as freshwater on the distillation container walls.
Methods: In this study, CI method was used for irrigating chili pepper in Shahrekord. This experiment was arranged as factorial experiment based on completely randomized design with four types of water (distilled water, drinking water and water with salinity of 4 and 6.5 dS/m) and three types of distillation container including transparent and dark plastic hemisphere, and pyramidal glass, as distillation areas. Two types of saline water used in this research were obtained from two regions of Naein in Isfahan province. The regions are desertic regions located on the margin of the desert areas of Iran and their groundwaters  are generally salty. After preparing the culture medium, the chili pepper seedlings were transferred to the field.
Some growth related characteristics and physiological parameters such as, total fresh and dry weight of the Shoots, total fresh weight of fruit, plant height, number of fruits, leaf relative water content and chemical indices including chlorophyll a, b and total chlorophyll, ion leakage, carotenoids, and water use efficiency and the volume of consumed water were measured and evaluated. In order to analyze the results, SAS software (version 1/9) was used. Mean comparison was also performed by LSD test.
Results: The results showed that, with increasing the salinity of water, the fruit’s fresh and dry weight, shoot weight, relative water content, carotenoids, water volume and water use efficiency decrease in comparison with distilled and drinking water, so that the water with salinity of 6.5 dS/m showed the most decrease in the studied indices. By increasing the salinity of the water inside the containers, the amount of evaporation decreases, resulting in decreased amount of fresh water produced on the distillation containers. In other words, the amount of available water to the plant decreases. Indices such as ion leakage, which indicates plant damage due to water stress, was also higher in the two saline water treatments (water with salinity of 4 and 6.5 dS/m). Also, the amount of carotenoids in the two saline water treatments was lower. By reducing available water for the plant (in other words, the more water stress for the plant) these indices become lower. Among the distillation containers, the highest values of the mentioned indices were observed in the pyramidal glass. The highest amount of water use efficiency was obtained in the two types of fresh water with an average of 4.4 kg/m3, and the lowest value of 1.6 kg/m3 was obtained in the water treatment with salinity of 6.5 dS/m. Finally, the results showed that if the distilled irrigation with water treatment with salinity of 4 and 6.5 dS/m and glass pyramid distillation was used, this method can supplies 24 to 27% of water requirement and the rest of the water has to be provided by supplemental irrigation.