Hidden potential

In farming, water can be a friend or foe.

Crops depend on it to thrive, but standing water can drown plants and delay fieldwork. On the other hand, when rain flows too quickly off a field, it can strip soil, nutrients and pesticides along the way.

Terraced-tiled systems have long been recognized as an effective solution to address both problems, reducing runoff and erosion while moving excess water off fields in a more controlled manner. Terraces act like speed bumps across a hillside, slowing and directing water into drainage tile—corrugated pipes buried beneath the soil surface. In Missouri, this type of drainage commonly relies on plastic risers at the intake, connecting surface water to the underground drainage pipe.

While effective at moving water, those open systems offer little protection against what the runoff carries into ditches, streams and waterways.

Now, University of Missouri researchers are rethinking drainage by replacing the traditional upright pipes with “blind” inlets, which sit below ground and filter rainwater through layers of gravel before entering the tile line. Considered a conservation drainage practice, the blind inlet—also known as a French drain—helps trap sediment and decrease nutrient and chemical loss while still removing water from the field as quickly as possible.

“Blind inlets have been tested in other states such as Minnesota and Indiana, but that research has focused on closed depressions and prairie potholes,” said Kelly Nelson, agronomy professor at the University of Missouri’s Greenley Research Farm near Novelty. “This is the first study I’m aware of in the Midwest that’s looked at blind inlets in a terraced-tile system. The soil types and drainage challenges in Missouri make it an important place to test this technology.”

Nelson and Dr. Gurbir Singh installed the first blind inlet on the Grace Greenley Conservation Showcase Farm in 2022, comparing this novel system to the traditional Hickenbottom risers and water-quality inlets. Looking at these systems under real-world conditions, MU’s work is evaluating best management practices in using them in a conservation setting, comparing their performance and measuring how much sediment, nutrients and chemicals leave the field.

In addition to Greenley Farm research, MU is also studying blind inlets on other demonstration sites in Nodaway, Shelby, Knox, Callaway and Montgomery counties.

So far, the findings support previous research from other states that show blind inlets greatly reduce sediment loads, 79%, and decreased phosphorus loads, 65%-85%, compared to a surface inlet riser. In addition, blind inlets also reduced the loss of herbicides such as 2,4-D, glyphosate, atrazine and S-metolachlor from 11% to 58%.

Along with water-quality benefits, blind inlets increase farming efficiency by removing interference from above-ground risers. Instead of having to steer equipment clear of those bright orange Hickenbottom pipes, growers can farm right through a blind inlet—planting, combining and even applying anhydrous ammonia.

“Farmability is important,” said Jeremy Redden, environmental program supervisor with the Missouri Department of Natural Resources’ (DNR) Soil and Water Conservation Program. “It’s going to be hard to change what farmers do in their everyday operation if it’s more of a hindrance than a help.”

Missouri DNR is partnering with Nelson’s team to expand the initiative at the farm level. Plans are to construct 20 on-farm blind inlets across northern Missouri, where more than 40% of the land is considered highly erodible and terraces are a crucial infrastructure. Agreements are still being finalized, but Redden said he hopes those installations can begin this fall.

“Our goal is to do whatever we can to provide better water quality across the state, and we believe that teaming up with Kelly Nelson and his team on these blind inlets can clean our water more effectively,” Redden said. “From the numbers we’ve already seen, blind inlets reduce sediment that’s going down the creeks, rivers and streams. And it reduces phosphorus and other nutrients that are also tied to the sediment.”

At all these sites, research will examine how blind inlets perform under Missouri conditions, including how quickly they drain water; how effectively they capture sediment, nutrients and crop protectants; and how different filter materials influence long-term performance. The work will also identify practical considerations for farmers, including cost of construction, maintenance needs, lifespan and compatibility with existing terrace systems.

“We’re still working on that agreement, but we want to get as many of these installed across the state as possible so we can continue the research as well as learn about the everyday farmability of these conservation practices in the field,” Redden said. “We want to get feedback from the growers who are farming with these inlets versus the old Hickenbottom-style risers.”

Though Missouri only has a few years of data from blind inlets, research in other states has shown they have a lifespan of at least eight to 10 years under tillage conditions. Nelson said the longevity is likely greater under no-till and conservation tillage, which is part of MU’s studies. Maintenance needs are minimal, typically only requiring occasional removal of accumulated sediment above the aggregate layer.

A blind inlet can be installed as new construction or in an existing terraced-tile system, as demonstrated in an on-farm example in northern Missouri. There, the process involved:

·    Excavating a trench that measures 5 feet wide, 60 feet long and 24 inches deep in the bottom of the terrace channel.

·    Lining the trench with geotextile fabric.

·    Adding 6-inch-diameter PVC pipe that has half-inch holes drilled every 5.25 inches facing downward.

·    Connecting the pipe to the main tile network.

·    Backfilling 70% of the trench with large, 3-inch clean aggregate (rock).

·    Covering the larger rock with small, 1-inch aggregate to ground level.

The size of the trench and pipe is based on the drainage area of the terrace and the desired water removal speed. Nelson said a sizing tool is being developed specifically for Missouri farms.

As far as expense, Nelson said this particular blind inlet was estimated to be around $2,500, but part of the ongoing research is to find the most cost-effective method and materials. Indiana’s Natural Resources Conservation Service adopted blind inlets in its conservation practice standards more than a decade ago, making them available for cost-share funds. Redden hopes that will soon be the case in Missouri.

“At DNR, we follow all of Missouri NRCS’s standard and specifications, but there is not a standard currently that has a blind inlet tied to a tile-terrace system,” Redden said. “This research is hopefully going to support adding that as a standard so we can someday assist landowners with the cost to implement these practices.”

Nelson emphasizes that conservation drainage is only one piece of the puzzle. Stacked practices are needed to fully address conservation and crop production goals. MU’s research is combining 4R nutrient management, no-till, terraces, cover crops and other practices that can allow farmers to maintain highly productive and flexible cropping systems while protecting natural resources.

“It’s not one thing or another. It’s a systems approach,” Nelson said. “The first goal is best management practices in the field. We’re synergistically looking at other practices to enhance our stewardship. I don’t think one can replace the other. Blind inlets, like these other practices, are a tool in our toolbox that can be used to help meet water-quality goals.”

Much of the work happens out of sight—beneath the soil, beneath the surface. But Redden said its impact could extend far beyond the field.

“Even though our primary goal is to improve water quality across Missouri, the benefits don’t stop there,” he said. “If blind inlets continue to deliver results, they could reduce sediment flowing into the Mississippi River and, ultimately, help shrink the hypoxic zone in the Gulf. These practices may make a small change at the field level, but they have the potential to make a much bigger difference.”

For more information, email greenleyfarm@missouri.edu and sign up for the center’s monthly newsletter at bit.ly/nm-reec_newsletter.