What it is
Drainage Water Management (DWM) is an NRCS-approved conservation engineering practice that manages water discharges from surface and/or subsurface agricultural drainage systems. DWM holds water in root zones when crops need it and drains it when there’s too much. There are multiple structures that can be used based on each site. An inline control structure is usually placed at the end of a tile system or at a property line and contains boards that can be manipulated inside the structure to control the water level. Additionally, a water gate valve can be installed below ground when there is significant elevation change and the inline control structure cannot impact this area.
How it helps
It manages the timing and amount of water discharged from agricultural drainage systems. Research shows that DWM as a Best Management Practice can significantly decrease nitrogen and phosphorus loads in subsurface drainage by reducing the overall volume of tile discharge. Unnecessary subsurface drainage and nitrate amounts leaving farm fields are reduced, improving water quality. A secondary benefit of DWM can be obtained when applying manure to crop fields. The structure can prevent accidental spills from reaching downstream bodies of water and impacting aquatic life.
The first step is to determine if DWM is right for your farm. DWM can be installed on existing subsurface drainage systems or on new systems. However, DWM is not suitable for every field and situation based on soil type and topography. Work with your local conservation office and tile contractor to determine proper placement and feasibility.
With appropriate management, DWM systems may also retain water needed for late-season crop production. To truly manage water table levels, they simply retrofit an existing tile system with a water control structure. Each structure controls an elevation-defined area, based on lay of the land and the tile system layout already in place. Structures are small, reasonably priced, and operating instructions are fairly simple:
- Before tillage, remove riser boards to drop water table levels about 10 days prior to planting fieldwork/operations.
- During the growing season, stack riser boards to potentially raise the water table high enough to provide capillary water to the crop root zone.
- Before harvest, if needed, remove boards to the lower the water table 10 days before fall fieldwork.
- After harvest, install riser boards to potentially raise the water table up even further – near the ground surface – to hold water and nutrients in the field/soil over winter.
- The drain outlet shall be raised prior to and during liquid manure applications to prevent direct leakage of manure from drainage pipes through soil macropores (cracks, wormholes, root channels).
Drainage Water Management (DWM) is an NRCS-approved conservation engineering practice that manages water discharges from subsurface agricultural drainage systems. A DWM structure holds water in root zones when crops need it while also allowing it to drain when there’s too much. It manages the timing and amount of water discharged from agricultural drainage systems and may also retain water needed for late-season crop production.