Tile removes water from your fields, but that water takes excess nitrogen along with it. That can add to higher nitrate levels in streams. And the closer the tile spacing, the more water and nitrate that will leave your fields.

Those are facts you must live with, says Eileen Kladivko, Purdue University agronomist. She has research data to back it up. A good portion of her data was collected on a field at the Southeast Purdue Agricultural Center near Butlerville, Ind., where tile was installed at different spacings on poorly drained Clermont soil in 1983, with an experiment beginning in 1984. The trial, spanning four decades, continues today. Tile drainage water from three spacings ­— 16, 33 and 66 feet — can be sampled, collected and measured. There is no collection point for a plot with tile at 132 feet. It’s the control plot.

Kladivko’s work in recent years shows there are ways to cut down on nitrogen loss that would otherwise leave in tile water. “That’s where cover crops come in,” she says. “Keeping a growing crop on the land during the months it’s not in cash crops makes a big difference.”

More N loss

Looking back over four decades, Kladivko notes the amount of water leaving tile lines varies greatly from year to year, depending on rainfall. In general, the site has received more rain during the past decade.

Related:Tile drainage can improve fieldwork timeliness, yields

“Concentrations of nitrates leaving in tile water didn’t vary among spacings, because crop yield differences among the three spacings were relatively small,” Kladivko says. “Since the volume of water, or drainage flow, differed greatly, total nitrate loss did differ with spacings. More water and nitrate loss occurred with narrower spacing due to greater drainage intensity.”

Originally, the field was in continuous corn and chisel-plowed for the first 10 years. Today, it’s no-tilled, and cover crops are included. Overall nitrate losses in pounds of nitrogen exiting in tile water today are significantly less than at times of peak loss in the 1980s, she observes.

Cover crops help

“The bottom line is that drain spacing matters in terms of potential nitrogen loss,” Kladivko says. “Rainfall amount matters too, especially when we have excessive rains.”

Nitrogen fertilizer rate and form of nitrogen applied also factor into how much nitrogen loss you can expect through tile lines.

“Cover crops reduce nitrate-nitrogen concentrations loads in tile water — that’s the good news,” Kladivko says. “There may be some development of this soil from drain installation, no-till or other effects over time. That is something we’re studying now. We don’t have an answer yet.”  

Related:Tile drainage benefits reach beyond yield increase

Cover crops can help reduce nitrate losses, especially during the months when there isn’t a growing cash crop in the field. “The cover crop takes up some of the nitrate that would otherwise leach out and leave the field through tile water,” she says.

In fact, results from the Southeast Purdue Ag Center indicate an average of 64% of tile drain flow and subsequent N loss occurs from November through March at this site. Include April, and it’s 80%.

“If we intensify drainage, we should also intensify management of that system — adding cover crops and perhaps considering controlled drainage — to reduce the ‘leakiness’ of the system for nitrates,” Kladivko concludes.