There’s more to drainage than just removing water (Keeping the Farm)
(Editor’s note: Ann Baldwin is a state conservation engineer with NRCS-Delaware.)
Delmarva farmers have historically depended on drainage to aid in successful crop production.
Drainage, whether surface (ditches) or subsurface (tiles), benefits farmers in several ways.
Removal of excess water after rainfall events in poorly drained soils protects crops from inundation damage. Drainage allows access to fields for timely planting and reduces the potential for soil compaction due to excess soil moisture.
While drainage practices provide many benefits to farmers, still, there are concerns about impacts to water quality.
When nutrients, such as nitrogen and phosphorus are applied to crops, even under prescribed nutrient management plans, any nutrients not utilized by the crops could be transported through the soil to the drainage system as excess water leaves the fields.
The drainage systems can carry nutrient-laden water to streams and ditches which could eventually reach our estuaries such as the Chesapeake and Delaware Bays.
Conservation drainage may be the solution that can give farmers proper drainage while also improving water quality.
The USDA Natural Resources Conservation Service and conservation partners are encouraging and promoting innovative practices associated with drainage that further reduce the potential for nutrients to enter receiving waters thus improving water quality.
One such conservation drainage practice is a denitrifying bioreactor.
What is a Denitrifying Bioreactor?
A denitrifying bioreactor is a buried trench filled with a carbon source — usually wood chips — installed at the edge of a field.
It is used to treat nitrogen in the drainage water.
A portion of the drainage water coming from tile drains or ditches is diverted through a water control structure to the bioreactor.
Microorganisms living in the woodchips consume nitrates in the water and expel it as nitrogen gas.
Paired with nutrient management and soil health practices, denitrifying bioreactors are proving effective in the efforts to further reduce nitrogen leaving crop fields.
Performance varies depending on size, location and a variety of other factors, but the average bioreactor on Delmarva has been found to remove at least 30-50 percent of nitrates from the water which flows through the bioreactor.
Additionally, bioreactors have no adverse effects on crop production and do not restrict drainage.
Delaware farmer, Edwin Alexander, worked with NRCS and ShoreRivers, a non-profit that helps protect and restore Eastern Shore waterways, to install a 24-foot-100-foot-by-3-foot deep bioreactor on the edge of his farm.
He has noticed a difference in the water that is diverted into the bioreactor and leaving it.
“So far, it works. When it gets down to other side, it’s clear.”
“Denitrifying bioreactors are part of a larger effort to change the perception of our agricultural drainage networks as only intended to remove excess water, to systems that can be used to manage water to reduce nutrient losses, boost crop production, and remove excess nutrients in drainage water,” said Tim Rosen, Director of Agriculture and Restoration for ShoreRivers. “As we try to make our farms more resilient to uncertain weather conditions, conservation drainage and denitrifying bioreactors, provide the necessary tools to manage water, improve water quality, and achieve crop production goals.”
Rosen also emphasized that denitrifying bioreactors are generally installed at the end of a tile or adjacent to a ditch system, which means they do not take much, if any, land out of production because they are small and fit within most buffers.
NRCS promotes coordinated conservation practices that help producers avoid loss, and control and trap nutrients and sediment at the edge of farm fields.
Denitrifying bioreactors hold great promise as a nutrient trap, reducing the flow of excess nitrates into local bodies of water, a significant water quality concern throughout the Chesapeake Bay Watershed.
ShoreRivers received an NRCS conservation grant to design conservation drainage practices for farmers at no cost throughout Delaware and are actively engaged in providing drainage design assistance for farmers throughout Delmarva. Farmers with designs can speak with their local NRCS conservationist about potential funding for certain components of the conservation drainage system.
For more information on conservation drainage, contact your local USDA Service Center.
To find your office, visit www.nrcs.usda.gov/contact and search the map by state.
1-800-634-5021 410-822-3965 Fax- 410-822-5068
P.O. Box 2026 Easton, MD 21601-8925