The impact of textural layering on water retention in sand profiles was evaluated through a series of laboratory column tests and numerical modeling. Alternating horizontal layers of coarse and medium sand were placed in 100-cm-long soil columns with three different layer thicknesses (5, 10, and 25 cm). A fourth column was constructed with a homogeneous mixture composed of equal amounts of coarse and medium sand. The soil columns were completely saturated and then allowed to drain to a water table boundary at the base of the columns. The changes of water storage with time were measured by weighing the columns during drainage and by measuring the soil water content profile after 120 h of drainage. The hydraulic properties of the coarse, medium, and the mixed sand were measured in the laboratory and also optimized using numerical simulations of the column tests. These properties were then used to simulate the longer-term drainage of deeper profiles, more typical of field conditions. The long-term simulations considered a 320-cm deep soil profile in which the upper 100 cm was composed of layers of the two sands or was a homogeneous profile of each sand or a mixture of the two. The lower 220 cm of the column was always coarse sand. A 320-cm homogeneous medium sand profile was also simulated. The laboratory tests suggested that, after 96 h of drainage, the 5- and 10-cm layered columns exhibited similar water retention that was higher than the 25-cm layered column or the mixture. The numerical modeling presented the same trends as the experimental results. Field capacity (FC) was assumed to have been attained in the simulations when the drainage rate reached 0.3 mm/d (10% of the mean daily potential evapotranspiration) at a depth of 100 cm. The water stored at FC was found to be 143, 145, 138, and 111 mm for the 5-, 10-, 25-, and 50-cm layered columns, respectively, much higher than that observed for the homogeneous medium (47 mm) and coarse (46 mm) sand columns. The time to reach FC after a large rainfall pulse (50 mm) was 100, 99, 72, and 45 days for the 5-, 10-, 25-, and 50-cm layered columns, respectively; again, a much longer time than that required for the homogeneous medium (24 days) and coarse (28 days) sand columns. These results highlight the role of textural layering in not only increasing FC but extending the time frame during which this water is available for plant growth.
1Department of Civil and Geological Engineering, University of Saskatchewan, Saskatoon, Saskatchewan.
2State Key Laboratory of Soil Erosion and Dryland Farming on Loess Plateau, Institute of Soil and Water Conservation, Northwest A&F University, Yangling, Shaanxi, China.
3Department of Soil Science, University of Saskatchewan, Saskatoon, Saskatchewan.
Address for correspondence: Dr. S. Lee Barbour, Department of Civil and Geological Engineering, 57 Campus Dr, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5A9. E-mail: firstname.lastname@example.org
Financial Disclosures/Conflicts of Interest: This study was funded by the Cumulative Environmental Management Association and by the Natural Sciences and Engineering Research Council. The authors report no conflicts of interest.
Received June 27, 2013.
Accepted for publication October 1, 2013.