نشریه آب و خاک
سال بیست و ششم شماره 6 (پیاپی 26، بهمن و اسفند 1391)

In recent decades، using drip irrigation has been developed because of water resources deficiency. As irrigation system design and its installation is expensive and time consuming، so its designing should be in a way which the system can supply plant water requirement. Nowadays، there are models that can simulate the soil moisture، according to different conditions. In this study، the performance of HYDRUS-2D has been assessed، by considering temporal variability of soil hydraulic properties. In a field under corn crop and irrigated with tape in south of France، soil moisture at every 10 cm depth until 150 cm of soil measured by a neutron probe was compared to simulated moistures by model according to two statistic indices، i. e. Root Mean Square Error (RMSE) and efficiency factor (EF). By considering soil hydraulic properties variation، RMSE values reduced from 0. 061 to 0. 022 cm3/cm3 and efficiency factor of model increased from 8% to 88%. Significant effect of these differences has been evaluated by using SPSS software and the result showed that the variation of soil hydraulic parameters in first irrigation was considerable and HYDRUS-2D model has a good performance in simulating the soil moisture at different depths. It is suggested that before installing system or implement of irrigation management، the system performance was evaluated by this model، and the best system management and design would be chosen.

The low irrigation application efficiency is the major problem of surface irrigation systems due to weak management and poor design. In this research، in order to analyze the performance of furrow irrigation system، a field experiment was conducted during maize growing season. Three furrow irrigation methods; conventional furrow irrigation، fixed alternate furrow irrigation and variable alternate furrow irrigation were considered to collect field data and، then، to evaluate the performance of WinSRFR (surface irrigation model). This model was calibrated and evaluated based on the experimental data with Zero-Inertia (ZI) and Kinematic Wave (KW) solutions. The sensitivity analysis of WinSRFR showed that the most sensitive parameters were inflow rate، cutoff time and parameters of the infiltration equation، respectively. There was a small difference between ZI and KW to estimate advance time، runoff and infiltration due to high field slope. The minimum absolute error for estimation of advance times was obtained about 1. 5% (0. 8 minute). The minimum absolute error in estimating runoff and infiltration were 5. 7 and 5. 0%، respectively. Using operations analysis of WinSRFR، the iso-performance contour plots of furrow irrigation system was obtained to optimize cutoff time and inflow rate under maximizing of application efficiency and distribution uniformity and minimizing of runoff and deep percolation. Application efficiency iso-performance contour plot of fixed alternate furrow irrigation، indicated by managing of cutoff time and inflow rate، application efficiency could be increasing from 54. 5% in current evaluation to 74%، provided water supply of Dreq. Also based on this contour plot، increasing of application efficiency more than 74% was impossible provided water supply of Dreq، under current furrow geometry parameters and it was possible with changing furrow geometry parameters.