Recently Dennis Bowman told farmers in west-central Indiana that one way to reduce nitrate flow out of tile lines is to install water control structures. Bowman, an Extension commercial agronomist with the University of Illinois, says this is just one of 10 possible ways researchers proposed to limit nitrate flow into tile lines after a recent study.

Once nitrates enter streams, they can wind up in the Gulf of Mexico. Farm fertilizer is one factor blamed for creating a dead zone in the Gulf.

Recently, farmers at an annual no-till breakfast in southeast Indiana engaged in a panel discussion about water control structures. Some of the discussion led to more questions than answers. Here are comments from two panelists: Brent Peak with Advanced Drainage Systems and Joel Wahlman, superintendent of the Southeast Purdue Ag Center (SEPAC) near Butlerville.

Question: What is the purpose of water control structures in a pattern tile system?

Peak: We’re trying to keep nutrients in the ground. The idea is to use a control box with gates to regulate water levels within the field. In the winter, you can allow the water table to rise instead of letting it drain out. That keeps nitrates left after the season in the field. Then you can adjust the gates in the spring to lower the water table so you can complete spring fieldwork.

Question: So do you raise the water table again in the summer after planting?

Peak: Yes. You keep it at a level where roots can grow down and get to water. So besides keeping nitrates from exiting the field through tile lines, you also provide water in the summer when crops need it.

Question: How many of these water control structures must be installed in a field?

Peak: We typically figure that you can control the water level on about 40 acres with one water control structure. If you have a larger field, say 120 acres, then you will need additional water control structures.

Question: What is a tile system going to cost per acre?

Peak: That is very difficult to say without knowing all the facts. It depends upon the size of tile to be installed, size of the main that the laterals drain into, and spacing. Are you going to space lines at 30 feet apart? Fifty feet apart? You can’t get a handle on estimated cost until you work out those details.

Question: Wasn’t a tile system with a water control structure installed at SEPAC?

Wahlman: Yes. In 2009 the Indiana Land Improvement Contractors Association installed a pattern tile system with a water control box in a small field on land that we acquired from the Indiana Department of Natural Resources. The installation over two days was a field day, so different types of tile machines were used to show how the various methods work.

Question: Is that field used for research on how tile systems work?

Wahlman: It has not been to this point. It is part of the land that we manage as farm ground. However, we have a long-standing tile line project going back three decades. Water is collected and tested for nutrient content at various points in the field. It has yielded information about farming practices related to nutrient loss. We’ve learned that nitrate losses through tile lines are typically much less if nitrogen is sidedressed instead of all applied in the spring.