New tiling technique stores water, nutrients in soil

Farm Forum

LUVERNE, Minn. – Farmers across the country use nitrogen and phosphorus to build nutrient-rich soil to maximize crop yields, but those same nutrients are being blamed on the growing dead zone around the base of the Mississippi River in the Gulf of Mexico.

Low oxygen levels in the gulf — referred to as gulf hypoxia — have grown to such a massive area that the northern Gulf of Mexico is said to be the world’s second largest dead zone for marine life. Scientists point to the nutrients washed from farm lands and through the Mississippi River watershed as the cause.

While farmers would prefer to keep the nitrogen on their fields to maximize crop yields, the nutrients often get washed into tiling systems, then carried into waterways, streams and rivers during rain events.

“By adding tile to the fields to increase production, what we’ve created is a leaky system,” explained Doug Bos, assistant director of the Rock County Land Management office in Luverne. “Nitrates are very mobile in the soil, and when you drain the soil, you’re pulling any extra nitrogen out and it ends up in the water.”

Bos said the demand for tile installation to help drain crop land in southwest Minnesota “has been exponential” in recent years.

“It’s just unbelievable as far as tiling requests,” he said. “If we don’t find ways to (reduce nutrient loss through tile lines) on our own, it is possible we could see new rules or regulations on it. Every drainage meeting I’ve been to, the speakers talk about the issues at hand.”

Just as it took years for gulf hypoxia to reach the level it’s at today, it may also take years to reduce the amount of nutrients getting into the river system and being carried downstream. Relatively new technology in Minnesota is hoped to help farmers capture those nutrients before they have a chance to escape.

The Rock River Watershed was recently awarded a grant from the Clean Water Fund, offered through the Board of Soil and Water, to establish a controlled drainage demonstration site along the Rock River, near Luverne. The project is a four-county effort, including Rock, Nobles, Pipestone and Murray.

Controlling drainage

Controlled drainage structures have been used in field tile systems across Iowa for at least 15 years, but the concept is just starting to spread through Minnesota. In fact, Bos said there are fewer than a dozen controlled drainage structures in place in farm fields across the state.

“Iowa’s really caught on by putting these in,” he said. “Minnesota and South Dakota are still in the demonstration and learning phase.”

Controlled drainage structures have the ability to hold water back in the field when production is unaffected, such as during planting and harvest. At the same time, they help during periods of drought by maintaining the water table and providing moisture and nutrients to growing crops.

“By holding water back, we also hold the nitrates in the soil,” Bos explained. “It’s a multiple-benefit practice — we prevent nitrates from ending up in the water, and we hold them in the field for the crops to utilize them.”

While controlled drainage structures may look different in each field based on the number of acres served, Bos said the structure at the demonstration site is about 5 to 6 feet deep.

“It’s like having four file cabinets together,” he said. “Given the size of the tile, there’s going to be four of these chambers connected in one box.”

The chambers hold water back until the farmer chooses to remove boards from the structure, thereby allowing water to be drained from the land.