Two-stage ditches with flood plains on either side of a ditch channel help slow down water flow and encourage sediment with nutrient particles attached to settle out on the flood plains created on either side of the channel. Water control structures that can be adjusted to keep tile line water in the field in the winter months instead of letting the water with nutrients and sediment flow out into the ditch also help keep down environmental issues.
There is no one answer, but instead practices that can be used to improve water quality, says Otto Doering, Purdue University Extension ag economist.
Another practice that can be a tool in the toolkit are biological reactors.
"The idea is to create an area where tile water must go through that is filled with a biological material, like wood chips, so that nitrates can be denitrifed there," says Jane Frankenberger, Extension specialist with Purdue Ag Engineering.
Other states have been examining this practice longer than Indiana. At the Farm Progress Show site near Decatur, Ill., University of Illinois researchers have studied bioreactors made of pits filled with corn cobs for several years. Early work with various bioreactors show positive results for reducing nitrates that eventually leave the field and wind up in water channels.
"It's not the wood chips that do the job," Frankenberger says. "It's bacteria that live on the wood chips that actually denitrify the substances. The key is to keep the area contained in the bio-reactor wet so that the process of bacteria doing their work can continue for as long as possible."
A bio-reactor was installed along with a two-stage ditch at Purdue's Throckmorton Farm near Romney by the Indiana Land Contractor's Association last summer. Frankenberger hopes to take measurements there in the coming years to gain knowledge about how effective these bioreactors can be.