|Van Genuchten, M. Th.|
Submitted to: Vadose Zone Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/19/2009
Publication Date: 5/14/2010
Citation: Siyal, A.A., Skaggs, T.H., Van Genuchten, M. 2010. Reclamation of saline soils by partial ponding: Simulations for different soils. Vadose Zone Journal. 9(2):486-495. Interpretive Summary: An unavoidable side effect of irrigation is that over time farmland becomes increasingly saline, resulting in reduced crop growth. To maintain productivity, it is necessary to periodically apply excess irrigation water so that accumulated salts are leached from the soil. It is desirable that this leaching be accomplished as efficiently as possible, using a minimum amount of water. A common obstacle to efficient leaching is that some sections of a field may leach more easily than others. In this research, we studied a leaching strategy called “partial ponding” in which a system of small ridges is used to control the application of water to different parts of the field, such that more easily leached sections are leached for a shorter period of time than other parts of the field. Our theoretical analyses found that by applying partial ponding to a sandy soil, it was possible to achieve water and time savings of 95% and 91%, respectively. The analyses also indicated water savings of 84% when applied to a loam soil, 99% for a layered sand over loam soil, but only 13% for a layered loam over sand soil. This research will benefit scientists, engineers, extension specialists, and growers seeking to develop more water efficient strategies for managing salinity in irrigated agriculture.
Technical Abstract: A traditional method of reclaiming salt-affected soils involves ponding water on a field and leaching salts from the soil through a subsurface tile drainage system. Because water and salts move more slowly in areas midway between drain lines than in areas near the drains, achieving a desired level of desalinization across the entire field requires that ponding continue long after areas close to the drains are already free of salts, thus causing an inefficient leaching process that wastes water. A partial ponding method of leaching was recently suggested to improve the leaching efficiency by up to 85%. In this study, we tested the partial ponding method for its potential to save water and time by simulating the leaching of salts from salt-affected profiles with various soil textures, tile-drain depths, and soil depths. Simulations for laboratory sand tanks and field conditions both showed that transport velocities midway between drains are greater under partial ponding than under total ponding because the local hydraulic head gradient is larger under partial ponding conditions. As the ponded area increases toward the drain, water originating from areas near the drain moves faster than water from midway between the drains. By adopting partial ponding, water and time savings of 95 and 91%, respectively, were found possible for a sandy soil. The method also showed water savings of 84% when applied to a loam soil and 99% for a layered sand over loam soil but only 13% when applied to a layered loam over sand soil.