Hold on to nitrates

Installing pattern tile systems in wet fields with suitable outlets is a paying proposition. If farmers didn’t believe it before, the advent of yield monitors in 1992 drove the point home. Maps typically indicate yield is reduced not only in the obvious wet spot, but also much farther out than many suspected.

The newest thing in tile installation is water control structures. They allow you to control the level of water beneath the surface throughout the year. While there could be some benefit to yield, the big advantage is in reducing the amount of nitrates in tile water.

“It’s a fairly new practice here, and it does require management,” says Mike Cox of the Natural Resources Conservation Service. He helped supervise installation of three structures at an Indiana Land Improvement Contractors Association project on land owned by the Southeast Purdue Ag Center.

“The idea is to reduce the amount of nitrates flowing out of tile lines into streams,” he says. “Control structures allow farmers to determine the level of water below the surface anytime during the year.”

Key Points

• Water control structures are a new practice in Indiana.

• The goal is to reduce nitrate losses through tile lines.

• Crops may benefit from extra water in some years.

Drainage becomes high-tech

“Controlled drainage is helping change the way we think about drainage,” says Jane Frankenberger, a Purdue Extension ag engineer and drainage specialist. GPS, RTK and autoguidance systems are helping installers do a more accurate job of laying tile. Then water control structures, each controlling up to 20 acres, put the farmer in control of managing water levels during the year.

“The big deal is that it affects water quality,” Frankenberger says. What people considering these structures need to realize, she notes, is that it’s about regulating water intake, not irrigation. The goal is to manage water levels in the field through use of the structures to minimize nitrate loss through tile lines during the year.

A typical management plan consists of closing the tile and keeping water in the field during the late fall and winter months, Cox says. Otherwise, without crops growing, nitrates are more likely to exit in tile water. Since the nitrates still eventually leave by other routes, you still need to apply the same amount of N per acre for corn.

Irrigation benefits?

A couple of weeks before the spring and fall work seasons, experts recommend letting the tile work. During the growing season, the current recommendation is to maintain the water level about 2 feet below the surface to provide adequate aeration for roots, yet capture some water that would normally flow out.

While it may be possible in some years to manipulate the system to help crops, Frankenberger stresses that this isn’t subirrigation, which requires closer tile spacing. Her goal is managing for water quality, although crops may benefit in the process.

Cost for a water control structure varies from $20 to $110 per acre served. There may be cost share available from the Farm Service Agency, depending upon rules in your county. For more information, contact your local soil and water conservation district office.


Man with a plan: Mike Cox supervises installation of two water control structures almost side by side in a field in Jennings County. Each structure serves a different drainage zone.

This article published in the September, 2010 edition of INDIANA PRAIRIE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2010.