WATER TABLE MANAGEMENT is the practice used to control the volume of water within the root zone in the soil profile. This is used to provide a soil moisture condition that will not only maximize crop yield, but also minimize the impact on water quality. Water table management provide both economic and environmental benefit. The economic benefits result from increased yield. The environmental benefits are a result of reduced loss of nutrients and fertilizer, especially nitrogen, from the field.
Controlled drainage provides important environmental benefits. It reduces soil compaction by heavy agricultural equipment and reduce surface runoff of over saturated soils as well as loss in highly important topsoil. Because of the solubility of nitrogen, uncontrolled subsurface drainage will increase the transport of the applied nitrogen from the field. The increase in nitrogen in natural water sources may have a negative impact on water quality. However, when the subsurface drains can be controlled, the loss in nitrogen can be greatly reduced.
Controlled drainage has been used in the Midwest of the United States of America from as early as the 1930’s. Since then, it became common practice throughout the world including countries like Canada, Australia, Italy, Spain and even Egypt. Subsurface drainage as well as water table management have enjoyed an abundance of attention from various academic institutions such as Ohio State University, USA, and Michigan State University, USA.
WATER TABLE is a term used to describe the surface of a saturated zone of soil above which the soil is not saturated and below it is saturated. This means that all the soil pore spaces of the soil below the water table will completely be filled with water. When the water table is too high, it minimizes the root zone, and reduce yield.
When water table management is done, the water table will be maintained near the bottom of the crop root zone, from where the water will move by capillary forces into the root zone. This will provide a continuous supply of readily available moisture to the roots of the crop. During periods of high rainfall, the system will be operated in drainage mode to prevent a sudden rise of the water table into the root zone and during drier time the system will be closed in order to store soil water.
Fields where the water table can be managed are accessible for farm equipment much sooner after a rainfall event than fields without. Drained soils have a well aerated root environment an enhanced availability of plant nutrients. It also reduces surface runoff and extend the growing season. Fields with water table management have shown increased yields and improved long term yield stability. Where conventional subsurface drainage systems may increase edge of field loss of some agricultural chemicals, such as fertilizer applied nitrate-nitrogen, in a water table management system the loss of these chemical can be lowered.
Soils with a stable water table will have a lower percentage of salinity in the topsoil. The improved movement of water thought the soil profile and the reduction of water logging, will result in the leaching of sodium out of the topsoil, into the subsoil from where the drainage pipes can transport the suspended salt away from the root zone of the crop.
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