2022 Volume 32 Issue 3 Pages 82
Recently, global warming and desertification have become critical environmental problems. The authors have been working in the dryland of Mongolia to develop technologies of efficient irrigation and greening systems by planting local medicinal plants with local materials and biomass. Field studies in the targeted areas have shown that rainfall and irrigation water is not retained in the soil and percolates downwards, resulting in insufficient moisture for plant growth.
This research aims at developing a water retention technology utilizing the capillary barrier concept for irrigated ground in drylands using local geo-materials. To optimize the system, clarifying the ground conditions including the layers’ thicknesses ratio (fine/coarse), grain size distributions, and watering method to maximize the water retention efficiency through experimental and numerical approaches is considered.
In the experiment and numerical analysis, the water retention efficiency of the capillary barrier system was evaluated based on the volumetric water content distribution to reflect the water availability. Various thickness ratios of double-layered soil profiles comprised of sandy soil in the upper layer (fine layer) and soil with a relatively larger grain size in the lower layer (coarse layer) were adopted. The variations and redistribution of the volumetric water content with time through the ground was measured, while a predetermined amount of water was supplied from the top at specific intervals. The main findings are delineated as follows:
1. The experimental testing of the capillary barrier with drip irrigation revealed that the volumetric water content at depth of 200 mm exceeded the target value of at least 0.1 on the third day of the experiment when watering twice a week with 1000 mL per irrigation is carried out.
2. From the numerical analysis, supplying water twice a week was enough to maintain the volumetric water content within a depth of 200 mm higher than the targeted value of 0.1. Consequently, maintaining these conditions of the assumed drylands is expected to ensure that plants can grow and survive.
3. Based on the numerical analysis, to maintain at least a volumetric water content of 0.1 extending up to 200 mm depth with supplying 1000 mL water twice a week, an optimum configuration with an effective grain size ratio RD10=5.2, mean grain size ratio RD50=3.9, and a thickness ratio X/L=0.1 of coarse and fine layers utilizing the adopted sandy soil materials was confirmed.
