Managing The Farm Drainage Outlet Year-Round

The benefits of farm drainage do come with some challenges.  Soluble forms of plant nutrients are able to move with soil drainage water and enter streams, rivers and lakes.  In sufficient concentration, these nutrients can cause harmful algae blooms that interfere with aquatic life and human uses of the fresh water supply.  One technology that can be used to limit the total annual load of soluble plant nutrients exiting farm drainage is controlled drainage.  Controlled drainage involves an in-line structure added to the outlet of a subsurface drainage system.  The structure allows the farm manager to artificially raise the outlet elevation and thus retain water in the field subsurface.  The outlet is not plugged nor is the outlet elevation raised to retain water up to the soil surface.  Controlled drainage structures can be adjusted to incrementally raise the elevation from the bottom of the field main to within 12-24 inches of the soil surface, depending on the time of year.

Controlled drainage is flexible and allows for management options year-round.   Farmers need dry soils during planting and other spring field operations, thus the controlled drainage structure would be set to free drainage 30-40 days prior to planting through the completion of spring field operations.  After spring operations are complete, the control structure would be set to conserve/retain water in the subsoil from rainfall to be used during dry periods of the summer, leaving 12-24 inches of drained soil at the surface available for rainfall.  If excess soil water is anticipated or received during the summer, farmers can lower the water level in the field by adjusting the control structure.  As harvest nears, the growing crop may have used all the retained water or farmers may need to return the structure to free drainage to lower the water level in the field.  Following harvest and fall field operations, farmers would raise the outlet elevation to 12-18 inches below the soil surface and hold it there until 30-40 days prior to spring planting.

Ohio data collected by Ohio State University and USDA-ARS shows modest crop yield increases resulting from controlled drainage when rainfall/soil moisture is retained and utilized by corn and soybeans.  Controlled drainage has also been shown to significantly reduce the total annual load of soluble plant nutrients exiting farm drainage, documenting that managing the farm drainage outlet year-round positively contributes to improved water quality from today’s production agriculture.

Source : osu.edu