Evaluation of evaporation from solar stills for crop water requirement of Maize in South East Tehran

In recent years in the field of agriculture and drinking water, Condensation Irrigation system combining with a solar desalination system and an irrigation system has been proposed. Condensation Irrigation system is a new idea in the field of fresh water supply. The importance of providing fresh water in the critical situation, using solar energy in purification of saline water, reduces the costs and supply of water. Considering the important issues of environmental pollution control in the form of fresh water resources indicates the need of further studies in this field. Desalination by solar radiation is one of the efficient ways to filter sea water and regarding the renewable solar radiation energy application as a way to provide sweetwater is regarded in line with sustainable development and adaptable to the environment. Since the ultimate goal of an irrigation system with any type of operational procedures is the preparation of crop water requirement, Therefore, evaluation of water supply by the irrigation system and crop water requirements is essential and is a criteria for acceptance or rejection the proposed system.
Solar Still is the major component in compression condensation system that is responsible for providing water. Solar Stills utilize solar radiation for sea water desalination. In this study, the potential of Solar Stills evaporation and crop water requirement of Maize were evaluated at different growth stages. This project studies were carried out in the South East of Tehran (Pakdasht). Accordingly four designs of Solar Stills were used. The Solar Stills dimensions were 30*30, 34*34, 40*40 and 45*45 centimeter. The material of the Solar Stills walls was made of Plexiglass sheets. To compare between crop water requirement and evaporation from Solar Still, Spring Maize plant is considered as the sample plant due to its row cultivating and it will be irrigated by condensation irrigation system. In the Cultivation period (125 days), the Maize evapotranspiration was calculated in CROPWAT 8.0 by using meteorological data of the study area. In this software, all calculations related to reference evapotranspiration are based on the FAO 56 principles and Penman-Monteith method. Information about plants characteristics such as plant name, date of planting, during periods of growth, the crop coefficient of different growth stages, characteristics of the depth of the root and management information for each stage of growth were entered in software according to the recommendations FAO56 publication and consultation with local experts. Finally, the crop coefficient and average of the plant evapotranspiration were calculated using software in millimeters per day and also millimeters per several decades of plant growth. Based on the observations, the maximum daily evaporation of the Solar Still occurred in late July (about 8.5 mm per day). The results of the Solar Still evaporation measurements showed high efficiency of this system in the study area and the positive influence of climatic conditions on the Solar Still.
The results indicate that evaporation rate of the Solar Still at all periods of growth is more than crop water requirement and in some growth stages, a square meter of Solar Still is able to supply about three meters of maize water requirement. Evaporation Variations in Solar Still follow the same process as crop water requirement variations and it has influenced atmospheric parameters and environmental conditions during growth period similar to crop water requirement. The amount of water vapor in the Solar Still is one of the most effective parameters on controlling the evaporation that achieving the optimum point to discharge water vapor in the Solar Still can significantly increases the power of Solar Still evaporation. The results of the present study in terms of evaluating Solar Stills evaporation potential compared with spring maize water requirement and it is noteworthy that in spite of the simplicity of the Solar Still in this project, evaporation from Solar Stills is higher than maize water requirement at all stages of significant growth and in some stages its ratio increased to three times. So regarding the performance of the compression system used in salt water, potential of solar stills was remarkable and the need for further studies in the field of promotion of evaporation potential of the Solar Stills reveal. By increasing the potential of Solar Still evaporation with new technologies, it is predicted that the amount of water produced by this system can be increased to an acceptable level.