Curious Iowa: What’s the purpose of field tiling?

Brian Carlson grew up familiar with Iowa agriculture as his father and grandfather farmed in Benton County.

Carlson, who farms corn and soybeans just south of Garrison, remembers his grandfather digging up parts of the family’s fields to site tile and remembers his dad installing tile himself when Carlson was young.

Tiling is an agricultural practice that involves installing a network of pipes underground to help remove excess water from the soil and improve field drainage.

Since he started farming in 1988, Carlson has been adding drainage tile to his own farmland, too.

“As I was able to buy a little bit of ground and had the financial ability, I tried to put in tile as often and as quickly as what I could afford to do,” he said.

Carlson estimates that about 80 percent of his 600 acres of land is tiled.

Carlson said using field tiling has helped him curb the erosion he sees in his fields.

On top of that, he said adding drainage tiles has boosted his yields. This past growing year specifically, he said the tile supported his soybean yields.

“You could actually see the higher yielding areas of the field in the area that was pattern tiled, versus the part of the farm that was not,” Carlson said.

Field tiling has been a common agricultural practice for decades, dating back a century.

In fact, remnants of 100-year-old clay field tiles can still be found throughout the state.

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But how did the practice start, how does it work and why is it so widespread? That’s what one reader asked Curious Iowa, a series from The Gazette that answers Iowans’ questions about the state and how it works.

What is field tiling?

More than 6 million acres of cropland in Iowa have moisture levels that affect agriculture’s productivity, according to Iowa State University Extension and Outreach.

When tiling is installed in fields, the pipes underground carry water away from the field, which helps prevent soil saturation and lowers the water table in the soil.

With less soil saturation, farmers and producers can plant their crops earlier, harvest later, reduce soil erosion in their fields, and improve soil health, resulting in better crop yields.

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Matt Helmers, professor of agricultural and biosystems engineering at Iowa State University, said the practice has been used for generations.

“A lot of our land was settled over 100 years ago, and many areas of Iowa were pretty wet. What was done at that time was to alter the hydrology in some cases, (like) digging drainage ditches and then putting in subsurface tile,” said Helmers, who also is director of the Iowa Nutrient Research Center. “When we first put in some of this drainage system, it was so that we could crop the pasture areas and pasture the swamp areas.”

Helmers said the practice is particularly important during wetter times of the year, like spring months, when fields are more saturated.

“We put in that drainage so that we drain the excess water,” he said. “We're only draining a portion of the water from the system.”

Helmers said the practice only drains the “drainable porosity,” or the volume of water released from the soil when the water table drops, which he said is about 5 percent of the total volume of the soil.

“We're trying to drain that so that we get air back into the soil, so that we don't negatively impact that crop production,” he said.

In its early days, Helmers said, drainage tile was often made of clay. Now, he said the drainage systems are made of corrugated plastic pipes, which is more efficient and easier to install.

He said the plastic pipes have small slits that allow water in, but are small enough to keep soil out of the pipes.

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Tiling can affect water quality

Although the practice is popular throughout Iowa — and much of the Corn Belt — because it can help curb erosion and increase yields, there can be environmental drawbacks to the practice.

Keith Schilling, a state geologist and the director of the Iowa Geographical Survey, which is housed at the University of Iowa, said these drawbacks mainly pertain to the tiles creating a path for nutrients to make their way into streams and rivers.

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Schilling said that “just about every field” in Iowa has these drainage systems, which typically use perforated pipes about four feet underground.

He said that field tile serves as the main pathway for contaminants — like nitrate — to make their way into Iowa’s streams.

The “water comes in (the pipes) and then the tiles are the primary way that water with nitrate is delivered to our streams,” he said.

Nitrate contamination in Iowa’s waterways has been a persistent issue in recent years, as the level of nitrate in the state’s water has risen due to more fertilizer use and nutrients entering waterways.

Ingesting water with nitrate in it — even at levels of 3 to 5 milligrams per liter — has been linked to several cancers. Iowa has one of the highest cancer rates in the country.

Schilling said there are some regions of the state where farming isn’t possible without these drainage systems. However, he said there also are parts of the state where tile has been installed and isn’t needed.

“I do see places where tile is going in, where I wonder why they're putting it in the first place. Because the water table would be plenty deep there,” Schilling said. “But I'd say in some areas, I see tile going in, I just wonder why they're putting it in the first place, because I can't see it doing a whole lot of good.”

He pointed to sloping ground in parts of the state where the tile is being installed.

“I can tell you that the water table is probably 10 or 15 feet below ground there,” Schilling said. “I just don't know why they're putting it in. So, it tends to be put in areas that are seasonally or perennially wet.”

Schilling said tiling work still is very prevalent in Iowa and in the greater Midwest, more than 100 years after it was first introduced in the early 20th century.

“And now we see new tile going in,” he said. “Oftentimes it's replacing the old tile that was there before. So, it's probably plugged, or it's not doing very well, or too many fields have hooked on to the drainage system, and it's just too much water and it can't handle it. So oftentimes, tile fields that have already been tiled once before.”

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Back in Benton County, Carlson said he hasn’t installed more tile on his land because of the financial commitment it requires. Carlson said he typically pays about $1,000 per acre for tiling.

But when he does pay for it, he has no regrets about installing it.

“I'm not sure I've ever heard of anybody that regretted that they did it after the fact,” Carlson said. “ It’s most people would ask why they hadn't done it sooner.”

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Olivia Cohen covers energy and environment for The Gazette and is a corps member with Report for America, a national service program that places journalists in local newsrooms to report on under-covered issues. She is also a contributing writer for the Ag and Water Desk, an independent journalism collaborative focusing on the Mississippi River Basin.

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Comments: olivia.cohen@thegazette.com