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United States Department of Agriculture

Agricultural Research Service

DARA Controlled Drainage Research Facility
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Summary:  Subsurface drainage pipe systems are used in agriculture, especially in the Midwest U.S., to remove excess water from soil, thereby improving crop growth conditions and field trafficability for heavy farm equipment.  A 1985 economic survey showed that the states comprising the Midwest U.S. (Illinois, Indiana, Iowa, Ohio, Minnesota, Michigan, Missouri, and Wisconsin) had by that year approximately 31 million acres (12.5 million hectares) that contained subsurface drainage systems.  The magnitude of the area involved indicates how important subsurface drainage is to the Midwest U.S. farm economy, without which, current crop production levels would be impossible to achieve.  While agricultural subsurface drainage systems provide important economic benefits, they also produce adverse environmental impacts, because the excess soil water intercepted by the buried agricultural drainage pipes often contains nutrients (nitrate/phosphate) and pesticides, which are discharged with the drainage waters into local streams, rivers, and lakes.
In order to mitigate the adverse environmental impacts of subsurface drainage, various onsite water management or treatment options need to be considered, evaluated, and implemented.  The practice of controlled drainage is one option that shows promise.  Controlled drainage is commonly employed in situations where the subsurface drainage system pipe network has a single outlet pipe.  A hydraulic control structure is then installed at some location along this outlet pipe. The hydraulic control structure allows the water table in the adjacent field containing the subsurface drainage system to be managed at a higher level than would otherwise be possible with conventional, unrestricted subsurface drainage.  A weir enclosed within the hydraulic control structure is what typically is used to regulate the water table level.  Studies in Midwest U.S. agricultural settings have found that controlled drainage can reduce the amount of nitrate (NO3-) released offsite by 15% to 75%, and these reductions are due to a decrease in subsurface drainage flow and not changes in drainage water NO3- concentrations.
More field test sites are needed to document the environmental benefits of controlled drainage.  To meet this need, a field research facility was installed in 2005 near the airport at the town of Defiance within northwest Ohio.  The site itself is located on farmland administered by the Defiance Agricultural Research Association (DARA).  Construction of this new research facility resulted, in part, due to a planned airport expansion, which will eventually encroach on northern portions of pre-existing test plots.  Much of the subsurface drainage pipe infrastructure was already in place, and with limited modifications (Figure 1), a research facility was produced having two pairs of replicated test plots (four total).  All four test plots have an area of 2.5 acres (1 hectare).  The drainage pipe infrastructure characteristics described in both older and more recent construction reports are listed as follows for all four test plots.

Test Plot 2 – drainage pipe diameter = 2 inches (5 cm); drain line spacing distance =
10 and 20 ft. (3 and 6 m); drainage pipe depth = 20 to 24 inches (0.51 to 0.61 m).

Test Plot 3 – drainage pipe diameter = 4 inches (10 cm); drain line spacing distance =
20 and 40 ft. (6 and 12 m); drainage pipe depth = 30 to 36 inches (0.76 to 0.91 m).

Test Plot 4 – drainage pipe diameter = 2 inches (5 cm); drain line spacing distance =
10 and 20 ft. (3 and 6 m); drainage pipe depth = 20 to 24 inches (0.51 to 0.61 m).
(Same as Test Plot 2.)

Test Plot 5 – drainage pipe diameter = 4 inches (10 cm); drain line spacing distance =
20 and 40 ft (6 and 12 m); drainage pipe depth = 30 to 36 inches (0.76 to 0.91 m).
(Same as Test Plot 3.)
   
Test Plots 2 and 4 are a replicated pair, and likewise, Test Plots 3 and 5 are also a replicated pair.  Every test plot is divided into two water table management zones, with each water table management zone having its own hydraulic control structure.  Figure 2 is a schematic of the facility showing drainage pipe, main conveyance pipe, and hydraulic control structure locations.

Figure 1.  Installation of 2 inch (5 cm) drain line at DARA site

 

Figure 2.  Field research facility schematic.  The four test plots are shaded in pink.  Blue lines represent pre-existing drainage pipes or main conveyance pipes.  Red lines represent recently installed drainage pipes or main conveyance pipes.  Small yellow boxes mark positions of hydraulic control structures.
 Crop production activities are the responsibility of DARA.  Corn and soybeans are alternated yearly, but the same crop is grown on all four test plots each year.  An initial site investigation, with elevation measurements, near-surface geophysical surveys, and a soil sampling/analysis program (Figure 3), was carried out to evaluate similarities and differences between the test plots in regard to topography, subsurface drainage system infrastructure, and soil properties.  The subsurface drainage flow and water quality are monitored at each hydraulic control structure.  Water quality measurements are obtained for nitrate, ammonia, filtered total nitrogen, phosphate, filtered total phosphorous, salinity, and total suspended solids.  Sixteen monitoring wells with pressure transducer sensors continuously measure water table depths within the test plots.  Baseline hydrologic data was collected beginning in Summer 2007 through Spring 2009 with all four plots having the same water table management strategy.  Beginning in the 2009 growing season, for each pair of replicated test plots, one of the test plots will employ controlled subsurface drainage, while the other will utilize conventional, unrestricted subsurface drainage.  The long term research goals for this field site include the following.

1.  Quantify the water quality impact and crop yield differences between conventional, unrestricted drainage and controlled drainage under similar field conditions.

2.  Measure the effects of drainage pipe diameter, drainage pipe depth, and drainage pipe spacing distance on environmental benefits and crop yields for both controlled and conventional, unrestricted drainage systems.  (This data will primarily be employed to develop design criteria for controlled subsurface drainage systems.)

3.  Determine the controlled drainage operational strategies that will optimize environmental benefits and crop yields.

 


Figure 3.  Site investigation equipment, (a) Trimble Navigation Limited, AgGPS 432 receiver, (b) Sensors & Software Inc., Nogginplus GPR unit with 250 MHz center frequency antennas, (c) Veris Technologies Inc., Veris 3100 Soil EC Mapping System, and (d) Giddings Machine Company, #25-SCT Model HDGSRPST trailer mounted drilling rig used for obtaining soil samples.



Last Modified: 7/20/2009
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