Clark Porter has spent years studying sustainable agriculture practices. Over the last decade, he’s implemented some of them on his farm near Reinbeck in rural Grundy County in central Iowa.

Porter has planted cover crops, installed saturated buffers and practiced no-till farming on his 310-acre farm.

More recently, Porter — who recently retired from the Iowa Department of Agriculture and Land Stewardship, where he was an environmental specialist — volunteered his farm to be testing ground for a new practice that could improve water quality and curb soil erosion.

Porter “serendipitously” met State Geologist Keith Schilling, director of the Iowa Geological Survey and a University of Iowa researcher, through a farmer they both know.

Last fall, Schilling and his team of researchers installed a saturated grass waterway on the Porter family farm to test its ability to slow the flow of nutrient-rich water, allowing it to pass through sediment before it exits a field, cleaner than when it started out.

The research

Keith Schilling, a University of Iowa research engineer, speaks in July 2023 about underground core samples taken across Iowa. He is now investigating the use of a saturated grass waterway in a Grundy County farm to see if it reduces nutrient runoff. (The Gazette)

Twenty years ago, Schilling was involved in a water quality study at the Neal Smith National Wildlife Refuge near Prairie City that investigated the benefits of converting row crop fields to native prairie. While conducting pre-conversion monitoring, Schilling said he observed that nitrates in a cornfield’s groundwater were “essentially removed.”

Years later, Schilling revisited the research at Kirkwood Community College, looking at the reduction of nitrates in the groundwater beneath the cornfields.

“We saw how nitrate concentrations in groundwater beneath the cornfields were greatly reduced when water flowed through the drainage way sediments,” Schilling said. “That was the foundation to say, ‘Hey, these sediments have a great capacity to remove groundwater nitrate. How come we’re not making use of that?’ ”

Through a partnership between the University of Iowa and Iowa State University, researchers are using a “stair-stepping” technique that slows water’s flow through tile under the grassway on Porter’s farm.

Schilling said the water goes through “check dams” that suppress the flow so it doesn’t “free flow” down the drainage tile. Those dams slow the movement of groundwater so the water loses nitrates before reaching the next check dam.

Schilling said grass waterways in fields are typically drained with underground tile, which prevents moisture from building up, which can contribute to “gullying” — what happens when soil erosion creates a drainage pipe.

Schilling said the stair-stepped water system is passive, but the operator can override the system by removing the gates in a control box.

Part of the research looks at ways water moves through different soil textures, comparing denser clay soil to a finer silt soil.

Real-world scenarios

Antonio Arenas, ISU assistant professor of civil, construction and environmental engineering, has been working with Schilling and the research team, collecting data to determine how the system would perform in real-world scenarios.

Arenas said when water’s flow slows down, it loses capacity to transport chemicals and properties along with it.

“There are many benefits that can be derived from slowing water down. By slowing water down well, you allow those sediments to be settled down, as opposed to continue traveling down the stream along with the water,” Arenas said. “So that’s the key. In hydrology, we use that concept quite a bit.“

Arenas said water slows when it flows through grass instead of soil, or when it flows over other vegetation or through forests.

In the system being tested by Schilling’s team, a gate at the bottom of the flow can adjust the water levels, allowing researchers to drain the system.

Schilling said the grass waterways are specifically used in rolling fields, like those often found in eastern and southern Iowa.

“Every time you see a rolling countryside field, you’re going to see these linear stretches of grass and those are going to be in the low areas for that purpose, for reducing soil erosion,” Schilling said.

The research is continuing through testing at additional sites and conducting a “robust economic analysis.”

“We will be looking to test the practice at other sites in the next few years, primarily focused in the eastern and southern portions of Iowa where grass waterways are a common conservation practice,” Schilling said. And “we will continue to monitor the practices at the Porter farm and document its performance in the next couple of years.”

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.