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Managing Soil Water (07/25/19)

This spring was a particularly tough time for many crop producers.

This spring was a particularly tough time for many crop pplsc.1 2roducers. They were unable to plant at the appropriate time due to wet field conditions. One way to manage excess water in the soil profile is with subsurface drainage (tile). Tile drainage does not remove “plant available” water from the soil; it removes “gravitational” water that would drain naturally if unimpeded by confining layers in the soil. The greatest benefits of tile drainage typically are realized in wet years. Drainage promotes deep root development and crops often have better access to soil moisture in dry years.

The installation and management of tile drainage is increasing in many parts of North Dakota, especially in the Red River Valley, due to seasonal, high water tables and soil salinity (soluble salts).  The salinity problem is related to naturally occurring salts lower in the soil profile. Soil salinity in the Red River Valley may potentially be an issue on more than 1.5 million acres. Other parts of the state also have salt issues, especially near field edges.

Tile drainage is a management practice that offers the potential to control and reduce salinity in poorly drained soils. Tile drainage has been successfully utilized on a wide range of soil textures, from sandy to clayey. Level fields can be drained as long as minimum grades of 0.08 to 0.1 percent are maintained for tile laterals and mains. A tile at 0.1 percent grade has 1 foot of fall per 1,000 feet. On level ground, this means that the tile depth would vary by 1 foot over 1,000 feet. Where topography or depth of the outlet ditch does not allow for a gravity outlet, pumped outlets are used, provided a surface waterway exists to discharge the drainage water.

Pipe depth and grade, pipe size and field layout are all extremely important in design and will determine the quality of performance of a tile system. The tile system must be designed and installed properly so it will perform well for many years.

Controlled, or managed, drainage systems incorporate structures that allow the producer/manager to raise the outlet elevation at strategic locations in the drainage system to control the release of drainage water and potentially maintain a shallower water table. Controlled drainage systems offer the potential to conserve soil water in the root zone after crop emergence. Managed drainage can reduce flows thus reducing the loss of dissolved nutrients (nitrogen and phosphorus) from the field. If the timing of rainfall is favorable, controlled drainage creates the potential to store water for drier periods during the growing season. “Subirrigation” is the practice of using the tile system to provide water to the root zone during the dry part of the summer. If a source of irrigation water is available and the drainage system is designed appropriately, water can be introduced into control structures, special inlets, or the sump of a pumped outlet to raise the water table and make water available to the crop.

 

Hans Kandel

Extension Agronomist Broadleaf Crops

 

     Tom Scherer

Extension Engineer

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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