Evaporation Reduction Potential in an Undisturbed Soil Irrigated With Surface Drip and Sand Tube Irrigation

The efficiency of drip irrigation is highly dependent on evaporation losses occurring from the constantlysaturated soil beneath emitters. Advent of subsurface drip irrigation is in part an approach to curb this inefficiency. Anirrigation method, Sand Tube Irrigation (STI), is proposed to increase the efficiency of Normal surface applied dripIrrigation (NI method) on permanent tree crops without the need for burying the irrigation tubing. The sand tube consistsof removing a soil core beneath the emitter and filling the void with coarse sand. A weighing lysimeter was constructed inthe laboratory and instrumented to directly measure temporal evaporation from large, undisturbed soil columns, 0.7 m indiameter and 0.8 m in height. Experiments were performed on six replicated soil monoliths to compare the two methods.The results indicated that, for four consecutive days after irrigation, there was a significant difference at the 95%confidence level between evaporation occurring from the NI and STI methods. After four days of evaporation, comparisonof water contents indicated that a higher amount of water existed between the depths of 0.2 to 0.55 m in the STI versus theNI method. Although drainage occurred from the macropore structure of the undisturbed soil monoliths, the STI methodshowed potential in retaining more water in the micropore structure of the lower depths, that would be available for plantuse rather than potential evaporation.