Bakhtiyar Karimi; Fariba Alinazari
Abstract
Estimation of wetting front dimensions enhances the water use efficiency and optimal use of water. Since, globally, most of the cultivated lands are not flat, full recognition of the moisture advance front is essential for proper management and operation of surface drip irrigation in these areas. In ...
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Estimation of wetting front dimensions enhances the water use efficiency and optimal use of water. Since, globally, most of the cultivated lands are not flat, full recognition of the moisture advance front is essential for proper management and operation of surface drip irrigation in these areas. In this study, two physical rectangular cubic models were constructed to measure the soil moisture advance front. The smaller model was used for experiments with lower discharge and the larger model was used for experiments with higher discharge. The experiments were carried out in four different slopes (0, 10%, 20%, and 30%), three soil types with different textures (light, medium, heavy), with three emitter discharges (2, 4 and 6 liters per hour). The results showed that the moisture distribution (for upstream and downstream of the emitter) was different in sloping lands (for different flow rates and different soil texture). Therefore, in relation to the position of the emitter and plant, drip system should be designed differently in the sloping land in comparison to flat lands. According to the nature of the sloping lands, the plant position was downwardly shifted and its exact positions are suggested for different scenarios (for different discharge rates, slopes, and soils) in this study. The results showed that the percent of downstream wetted radius in sloping lands for the three types of heavy, medium, and light textured soils were between 49.2-81.5%, 49.2-76%, and 48.3-70.7%, respectively. These values for the percent of the upstream wetted radius of the emitter ranged between 18.5-50.8%, 24-50.8%, and 29.3-49.7%, respectively. The results of this study can be used as a general guide in the design of drip irrigation systems in sloping land to determine the plant and emitter position relatively accurately.
Bakhtiyar Karimi; Fariba Alinazari
Abstract
The wetted profile pattern is an important factor to consider when designing and managing a surface and subsurface drip irrigation systems. The knowledge of the pattern dimensions is imperative in choosing the suitable spacing between emitters and the correct distance between laterals. The experiments ...
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The wetted profile pattern is an important factor to consider when designing and managing a surface and subsurface drip irrigation systems. The knowledge of the pattern dimensions is imperative in choosing the suitable spacing between emitters and the correct distance between laterals. The experiments were carried out in a transparent plexiglass tank (0.5 *1.22 *3 m) using three different soil textures (sandy clay, sand clay loam, and sandy loam). The drippers were installed at 3 different soil depths (15, 30 and 45 cm). The emitter outflows were 2.4, 4 and 6 Lhr-1 with irrigation duration of 6 hr. In this study, using the data obtained from the laboratory experiments and conducting the nonlinear regression analysis using Microsoft Excel Solver tool 2010, an empirical model was developed to predict the horizontal distribution of the wetting front for different application times. The suggested model includes estimation of the wetted radius at the top and bottom of the emitter horizontal axis as a function of emitter discharge, saturated hydraulic conductivity, water application time, soil bulk density, emitter installation depth, initial soil moisture content, and the percentages of sand, silt, and clay in the soil. We pursued a similar procedure in developing empirical formulas for estimating the wetted radius at different soil depths (by optimizing the coefficients of Equations) to predict the full shape of the wetting pattern. The best performance of the model was related to the depth of zero (on the emitter positioning axis), where the values of RMSE, MAE, and R2 were 2.15, 1.7 cm, 14.85 % and 0.92, respectively. The lowest performance of the model was related to the depth of 20 cm from the emitter, where values of RMSE, MAE, and R2 were 3.93, 3.26 cm, 37.55% and 0.75, respectively (R2 coefficient was significant at 5% level). The results of this research showed that the suggested model predicted the full shape of wetting pattern with acceptable accuracy. Considering these models in designing subsurface drip irrigation systems could improve system performance.