These researchers used observations of water movement from laboratory and field experiments over the last three years to create a model to predict the redistribution of water in the soil following irrigation or rainfall. They specifically studied what causes the water to break up into narrow channels called fingers that can move much deeper into the soil, even when there are no apparent cracks or holes in the soil.
The model assumes all soils are unstable during this redistribution of water, but only coarse-textured soils will form fingers capable of moving significant distances. For example, laboratory experiments in coarse sandy soil showed that as little as 2 inches (5cm) of water added to dry soil would create fingers that could move more than 3.2 feet (1m). In addition, the wetted pathways formed by the fingers remained 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, professor, University of California-Riverside, and principal investigator on the project, which was sponsored by the U.S.-Israel Bi-national Agricultural Research and Development Fund (BARD).
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 watering might decrease the possibility of fingering near the surface.
Vadose Zone Journal, www.vadosezonejournal.org, is an electronic, peer-reviewed, international publication published by the Soil Science Society of America (SSSA), with the Geological Society of America as cooperator. The research and assessment needs of the vadose zone have grown in response to the pressure of increasing human impacts, prompting this new publication for a diverse range of scientists and engineers. The mission of the Vadose Zone Journal is to disseminate information about the physical, chemical and biological processes operating in this zone and to facilitate science-based decision making and sustainable management of the vadose zone.
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Vadose Zone Journal