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Tiling and nutrient runoff: An uneasy relationship

Phosphorus runoff can be a big issue in tiled fields.

Chris Torres, Editor, American Agriculturist

May 9, 2023

5 Min Read
machinery sits in field waiting to dig for tile installation
READY TO TILE: Field tiling is an obvious solution for some producers who work fields that are constantly flood prone.Photos courtesy of Joshua Faulkner

When Josh Faulkner talks to farmers about climate change, he understands some people have questions about the science.

“But everyone agrees that storms are heavier, more frequent, and they want to know what to do,” he said.

Field tiling is an obvious solution for some producers, especially those who work fields that are constantly flood prone. But it can also lead to more nutrient losses, potentially costing a producers’ bottom line and leading to more water-quality problems.

Speaking at a recent tile drainage event presented by Cornell Cooperative Extension, University of Vermont Extension, Partners for Healthy Watersheds and others, Faulkner said that documented nutrient impacts from tiling are concerning.

“It took a while for science to catch up to what’s happening here,” he said.

In Vermont and other states across the Northeast and mid-Atlantic, phosphorus is a big issue because too much of it flowing into waterways can lead to excess algae growth and too little dissolved oxygen in water that can kill fish and other wildlife.

It was once thought that phosphorus runoff in tiled fields was not an issue because phosphorus normally binds tightly to soil and stays in place, especially in fields with best management practices installed. But research from New York in the 1990s, and the western Lake Erie basin, has found excessive amounts of phosphorus leaving tiled fields, he said.

One reason: timing. Phosphorus loads increase from big storm events, Faulkner said, especially during the non-growing season as plants are not there to take up nutrients. He cited the 2017 Fourth National Climate Assessment that stated that from 1958 to 2016, the number of very heavy precipitation events increased 55% in the Northeast.

No-tilled fields, especially clay soils, are prone to phosphorus runoff, he said, because there are more root channels for water to flow — especially fast-flowing water — leading to more potential nutrient runoff.

“It’s the tillage in a tiled system that breaks up those channels,” Faulkner said.

And when the water table is high, oxygen in the soil gets depleted, and the soil will release more phosphorus. “These are years when drainage tile just can’t keep up,” he said.

Manure, rather than synthetic fertilizer, can cause bigger issues because it releases nutrients slower. Data show that phosphorus losses in tiled fields tends to be higher, Faulkner said, except in fields where the nutrients are injected. “Because when injecting, it has a better chance to bind with the soil,” he said.

Deeper dive

Laura Klaiber, a research assistant at Miner Institute — a 500-cow, 1,250-acre research facility in northern New York — has been doing research on tiling since 2013.

“Despite drainage not being a new invention, there really has been minimal water-quality research, not just in the Northeast, but including the Midwest," Klaiber said.

Of the research done, most of it has only looked at tile-drained fields and what's coming out of those tiles.

“But when you drain a field, a lot of that water that would have come from the surface is now going through the tiles,” Klaiber said. “If you measure a tile-drained field and measure what's coming out of the tiled end versus what's coming out of the surface, that doesn't necessarily tell you what the field is doing.”

In 2013, four research plots were installed at the institute. The plots were on 5% sloped fields, 75 feet wide by 150 feet long. Two tiled fields and two undrained fields were monitored for almost two years. At the base of the slopes, a cut PVC pipe collected surface water and delivered it to manholes for collection.

In a saturation or snowmelt runoff event, Klaiber said the system could collect 130 samples.

On average, the study found an 86% decrease in surface runoff in the tiled plots but 67% more overall water flow.

Despite there being more water flow, 50% less phosphorus — 0.06 pounds per acre in tiled fields compared with 0.12 pounds per acre in untiled fields — came out of the tiled fields. But the type of phosphorus is key to understand, Klaiber said.

The study showed that the amount of soluble reactive phosphorus, the stuff that plants take up and can also cause algae blooms in water, averaged 84.2 grams per hectare. But the amount of particulate phosphorus, the stuff that sticks to dirt, was higher in tile-drained fields.

An even larger field-scale study was done across two 6-acre fields. Tile drainage was installed in one field at 4 feet deep, 25 feet lateral spacing. Spring manure and fertilizer applications were done with immediate incorporation.

The surface runoff and tile drainage were measured year-round using a flow-based sampling method.

Five years of data were collected, Klaiber said, which showed that tile-drained fields released more water. Consistently, though, while the tile-drained fields had a much smaller fraction of total phosphorus load, more of it came from sediment and organic sources — manure — about a quarter-pound-per-acre loss.

Klaiber said research like this will eventually help producers manage their nutrients better not only for the environment, but also for their bottom lines.

“Drainage research and monitoring is challenging,” she said. "Point sources, you’ve got water treatment locations; you know where that water is coming out of that you need to sample. With the fields, you see very different situations related to weather, manure, other things.”

Future research, Klaiber said, will look at the incorporation of a winter rye cover crop in no-till corn and looking at specific practices and their impacts in tiled fields.

Possible fix 

Faulkner said that tile drain filters could offer a possible solution to treating tile drainage water.

The idea is to use a filter media — one example is a media consisting of 8% metal shavings, the rest pea gravel — and force water through it to catch dissolved phosphorus.

Initial studies, Faulkner said, of a 10-by-12-foot filter 24 inches thick removed 97% of soluble phosphorus. “So it has worked really well,” he said, adding that the practice has been approved as a Natural Resources Conservation Service interim conservation practice in Vermont.

“We’re excited about this,” he said.

About the Author(s)

Chris Torres

Editor, American Agriculturist

Chris Torres, editor of American Agriculturist, previously worked at Lancaster Farming, where he started in 2006 as a staff writer and later became regional editor. Torres is a seven-time winner of the Keystone Press Awards, handed out by the Pennsylvania Press Association, and he is a Pennsylvania State University graduate.

Torres says he wants American Agriculturist to be farmers' "go-to product, continuing the legacy and high standard (former American Agriculturist editor) John Vogel has set." Torres succeeds Vogel, who retired after 47 years with Farm Progress and its related publications.

"The news business is a challenging job," Torres says. "It makes you think outside your small box, and you have to formulate what the reader wants to see from the overall product. It's rewarding to see a nice product in the end."

Torres' family is based in Lebanon County, Pa. His wife grew up on a small farm in Berks County, Pa., where they raised corn, soybeans, feeder cattle and more. Torres and his wife are parents to three young boys.

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