عنوان مقاله [English]
نویسندگان [English]چکیده [English]
A significant reduction in the quantity and quality of available water resources and locating Iran in arid and semi-arid area lead to pay attention to modern irrigation systems to increase irrigation efficiency and water use efficiency. Subsurface Drip Irrigation (SDI) is one of these methods which bring losses to a minimum value. The success of a drip irrigation system depends on its design and implementation. The aim of this study was to evaluate the efficiency of subsurface drip irrigation systems implemented in citrus orchards of Kordkuy city and assess the strengths and weaknesses of the system and provide corrective measures for improving its efficiency. The study area covers 6 hectares of Citrus groves and 3 hectares of Peach orchards. In order to evaluation and monitoring the irrigation system in the studied garden, a manifold system was randomly selected and four lateral lines located at the first, in one third and in two thirds of the length from the derivation line and in the last lateral line were selected. Then four points (the first, in one third and in two-thirds of the length of the lateral line and in the last) were selected according to ASAE standard. In the next step, the soil around each side removed enough to allow measure emitter discharges. The volume of water that discharged from all emitters during one minute were measured. The pressure at the inlet and last of lateral tubes were measured by Manometer. For evaluating the performance of the SDI system, the ASAE evaluation criteria (i.e. coefficient of variation of discharge, statistical uniformity coefficient, coefficient of variation of pressure, coefficient of variation of discharge considering the flow hydraulics and the overall performance of the emitter) were calculated. Measurements were performed twice during the season and at the end of the season.
The results of the measurements showed that the discharge rate and emitter’s pressure is not uniform, this difference in values can be occurred due to the following factors: the friction losses, emitters clogging due to soil particles and roots or mineral deposits. The second factor that is a great concern of evaluated system design is connecting the lateral tubes at the end of each block like a circuit, so that the water circulates in each block. This causes the pressure distribution disoriented in the entire of irrigation system. According to the calculated indicators presented in the tables in this article, the coefficient of variation of the evaluated system is unacceptable. The main reason of high coefficient of variation of discharge (25%) is emitter malfunctions. The mean value of emitter discharge is less than the nominal amount (4 liters per hour) which approve above mentioned claim. The average hydraulic pressure of systems for citrus groves and peach orchards were 23 m and 33 m, respectively, which these values are very high for a drip irrigation system. The main reason for the high average hydraulic pressure was removing the disk filters by operator two years after start of system operation. The operator has felt the system cannot provide the required water for trees during the irrigation time and the moisture does not appear at the soil surface. Therefore, he wanted to increase the pressure of the system to increase the emitter discharge by removing disk filters. Although this slightly influenced on emitter discharges, but since the emitters are adjustable, this will only waste the energy. The emitters used in this project are adjustable type and increasing of pressure does not affect on the emitter discharge rate. Therefore, by increasing the pressure up to 5 bar, the discharge of the emitter will not increase more than 5.4 liters per hour. Another flaw in designing of this irrigation system was the installation of filtration station outside the garden. The height difference between the filtration station and the garden is about 15 meters, which is one of the main reasons of non-uniform distribution of pressure in the irrigation system.
Generally, the evaluation results indicated that the observed defects in this system caused by three main factors in the design, implementation and operation of the system. The most important factor causing non-uniformity of emitter discharge is clogging of emitters which is about 80% in this system that caused by several reasons. In design of the system, circuiting of tubes at the end of the blocks in the garden, leads to pressure fluctuations and non-uniformity of pressure distribution in the system.