Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Modeling and laboratory evaluation of evaporation and moisture redistribution for drip/trickle and "sand tube irrigation" using undisturbed and reconstructed soils

Auteur : Meshkat, Masoud

Université de soutenance : University of Kentucky

Grade : Doctor of Philosophy (PhD) 1997

Résumé
Drip irrigation is one of the most efficient systems in delivering water to the plant root zone. Research has shown that the saturated or nearly saturated surface beneath the emitter may contribute to significant amount of evaporation. In a dry and hot climate the wet surface significantly contributes to evaporation. To increase the efficiency of surface applied drip irrigation on permanent tree crops a "Sand Tube Irrigation, STI" method was developed tested on large reconstructed and undisturbed Maury silt loam cores. The sand tube method consists of removing a soil core beneath the emitter and filling the void with coarse sand. A large (1 m in diameter by 0.7 m high), counter balanced, weighing lysimeter was designed and instrumented to directly measure temporal evaporation. Integrating the water tank as part of the lysimeter resulted in measurement of evaporation with an accuracy of 20 g (0.04 lb) for the 800 kg (1764 lb) soil cores used. A fabricated heater was used to create day and night temperatures. Evaporation was continuously measured during irrigation and for a period of three days after irrigation ceased. Thermocouples were used throughout the soil profile to detect the temperature variation and also to determine temporal movement of the wetting front. Twelve experiments were completed consisting of three replications of reconstructed and undisturbed soil cores to contrast traditional surface drip irrigation and the STI method. The result of the reconstructed soil tests indicated that for the surface applied drip irrigation method, on the average 30% of the applied water evaporated during the four day period after irrigation. The STI method, during the same time period, resulted in approximately 3.7% of the applied water being evaporated. Statistical analysis of the undisturbed soil samples showed that significant differences exist between evaporation of the surface applied irrigation and the STI method. A finite element, two-dimensional model, SWMS$\sb-$2D, capable of simulating unsaturated/saturated flow in porous media was used to model the sand tube method in the reconstructed soil. SWMS$\sb-$2D, implemented in a three-dimensional axisymmetric form, was used to simulate the infiltration, moisture redistribution, evaporation from the soil surface and rise of water inside the sand tube. Model simulations were compared to laboratory measurements. The simulated values of water height inside the sand tube and temporal position of the wetting front in both lateral and upward directions closely matched the experimental data. Evaporation simulations were approximately in agreement with measured values.

Mots clés : Agronomy, Applied sciences, Soil sciences, Environmental engineering, Biological sciences, irrigation Agricultural engineering

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