The researchers used observations of water movement in the laboratory and in a field experiment to help create a model that describes the final position of the fingers as a function of measurable soil retention and hydraulic functions, plus relationships describing finger size and spatial frequency.
The model assumes that all soils are unstable during redistribution, but shows that only coarse-textured soils containing a lot of sand will form fingers capable of moving more than a few inches deeper than the rest of the infiltrating water.
Laboratory experiments in a sandy soil showed that as little as 5 cm (2 inches) of water added to a dry soil would create fingers that could move more than 1 m (3.2 ft) during redistribution. In addition, the wetted pathways formed by the fingers persisted in soil for long periods of time, and were able to channel subsequent water applications as long as a month later.
"These findings help explain field observations of deep chemical movement in soils without cracks or holes that have baffled other scientists and myself for over 20 years" said William Jury, Distinguished Professor of Soil Physics in the department of environmental sciences at UC Riverside and Principal Investigator on the project.
The research discovery has serious implications for agricultural water management in coarse-textured soils. Fingering can move water and agricultural chemicals below the crop root zone, which is costly and inefficient, and can increase the possibility of ground water contamination. The researchers suggest that longer and less frequent water applications might decrease the possibility of fingering near the surface.
The research, conducted in 2000-2002, was sponsored by the US-Israel Binational Agricultural Research and Development Fund.
Vadose Zone Journal is published by the Soil Science Society of America and is an outlet for interdisciplinary research and assessment of the vadose zone, the mostly unsaturated zone between the soil surface and the permanent groundwater table.
The UC Riverside Department of Environmental Sciences offers B.S. and B.A. degrees in Environmental Sciences, and M.S. and Ph.D. degrees in Soil and Water Sciences. The department is part of the College of Natural and Agricultural Sciences. The forerunner of the department was an agricultural chemistry research unit in the world-renowned California Citrus Research Center and Agricultural Experiment Station established in Riverside in 1907.
The University of California, Riverside offers undergraduate and graduate education to nearly 16,000 students and has a projected enrollment of 21,000 students by 2010. It is the fastest growing and most ethnically diverse campus of the preeminent ten-campus University of California system, the largest public research university system in the world. The picturesque 1,200-acre campus is located at the foot of the Box Springs Mountains near downtown Riverside in Southern California. More information about UC Riverside is available at www.ucr.edu or by calling 909-787-5185. For a listing of faculty experts on a variety of topics, please visit http://mmr.ucr.edu/experts/.
Journal
Vadose Zone Journal