Research Highlights

Water Table Data May Help Manage Drainage

By Laura Temple

Soil moisture flows from the water table toward plant root zones, according to Brian Leib, associate professor of biosystems engineering at the University of Tennessee. He focuses on irrigation research to help farmers use water efficiently, but he recently expanded his research to look at drainage, as well.

“After several dry years, Tennessee farmers added irrigation to many fields about a decade ago,” he explains. “Then more recently, after a few very wet years, they have started adding tile drainage to fields along creeks and in other areas prone to waterlogging.”

He notes that most of that tiling in the region usually is installed at a much shallower depth than is common in the Midwest, about 24 to 30 inches below the soil surface. However, it has helped farmers get into historically wet fields for spring field work and planting much earlier, which supports soybean yields.

“Farmers noted that their tiled fields yielded well, even without irrigation,” Leib says. “This observation, along with the ability to open and close the drainage tiles with a swivel pipe, raised questions about how best to manage drainage in Tennessee soybeans to avoid waterlogging and dryness.” 

The Tennessee Soybean Promotion Board funded Leib’s efforts to provide initial answers to those questions. 

“I remembered my master’s thesis research in Colorado, where I learned that a high water table provided moisture crops needed, even without rain or irrigation,” he says

He hypothesized that understanding the water table depth in these Tennessee fields could help farmers optimize water use. Allowing tiles to drain when the water table is high, usually in the spring, could manage against waterlogged soils. Then, closing the drains to preserve water as the water table drops could support crop yield later in the season, when weather is often dry.

Leib had developed an app that provides real-time soil moisture data from sensors in the field and separated water from rainfall and irrigation. With the addition of one piece of information, he added the ability to monitor the water table in the app. 

Through a few years of research and monitoring, he observed that the water table stays low in the fall. Opening drains several weeks to a month before planting allows fields to dry out, creating conditions that encourage strong crop root development. As the crop grows and requires more water, closing the drains keeps tiling from impacting soil moisture levels. 

“During one year of the project, major rain events caused the water table to jump up during the summer, so opening the drains again could have helped manage waterlogged soils,” he says.

He also noted that keeping drains closed during the winter helps limit water movement when soils are most prone to losing nutrients. 

“We saw drainage improve soybean yields in wet fields,” Leib reports. “However, I hope to continue monitoring water table depths in both tiled and irrigated fields to better understand the interaction between the water table, crop water use at different growth stages and yield.”

He says more data is needed to validate the drainage management observations. He also believes the water table information could improve irrigation timing management. 

Published: Mar 18, 2024