Considering the climatic conditions of Iran, the most leading barrier for production boost is the limitation in water resources. Since the major part of
the water attained is utilized in the agricultural sector and on the other hand the 'Nater use efficiency on the farm is only about 30 to 35 percent, the most
proper use of water resources must be considered as the main axis of progress. The possibility of extending the area under cultivation up to three times the present area, provided that water is supplied, adds to the importance of the
subject to a agreat extentSince microirrigation system is an ideal potential in efficient water application, it is considered to be a promising way in the
direction of the best usage of water resources. The need for development of the area under cultivation in conditions of limited water resources expresses
the necessity of attention to be paid to the development of such systems. In the direction of quantity improvement one must also pay attention to the way
projects are performed. In this study, the determination of evaluation factors such as potential and actual efficiencies of water application as well as
uniformity coefficients were the main objectives. To carry out the research objectives, five existing micro-irrigation systems in Semnan province were
taken into account from the view point of planning, performance and management. Each system was evaluated four times during the irrigation
season. The evaluation parameters were measured on the basis of Soil Conservation Services (SCS) method and the system designs were controlled
against design measures. By measuring eight pressures and the discharge of 32 emitters in one unit of irrigation and controlling the pressure in the whole
irrigation system in operation, the uniformity and potential efficiency of water
application were determined. System "A" with an average manifold emission uniformity (EUm) of 91.8 percent, average efficiency reduction factor (ERF) of 0.89 and an average system emission uniformity (EUs) of 81. 7 percent,
possessed the best performance among the selected systems evaluated. System liB" with EUm of 81.7 percent, ERF of 0.69 and EUs of 57.2 percent had the
lowest performance. Average EUm on all the manifolds under investigation was about 87.3 percent with an ERF of 0.79 . The amount of EUm, in fact,
shows the ability of a micro-irrigation system unit from the view point of uniform distribution of water. The low amount of ERF indicates the problem
of unfamiliarity of farmers and the necessity for education of system management. The average measured EUs and PELQ were about 69.42 and
62.48 percent, respectively. The amount of PELQ, on the one hand, is related to manufactures coefficient of variation for individual emitters and on the
other to the management of the system.
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