Tiling isn’t the best solution to managing excess water on all cropland, advises Jeff Hemenway, a South Dakota Natural Resources Conservation Service soil health specialist.

Tiling is most effective in a couple of situations:

On fairly flat fields where the water table rises nearly to the surface.

On fields where there’s a heavy clay layer below the topsoil that keeps nearly all the moisture that accumulates during the year in the upper layers of the soil.

But on other fields with other types of soils and in rolling fields, tiling may only treat the symptoms of ineffective water management.

INSTALLATION: A crew rolls a drain tile main line. Tiling will improve water management in some fields and in some soils, but it has its limitations.

“Our Web Soil Survey provides an evaluation tool to determine if drain tile is really necessary,” Hemenway says. “In some cases, water may sit on top of the soil, but moisture isn’t excessive. It’s just not properly infiltrating the soil.”

Water ponding often occurs when soil structure is degraded by tillage. Ideally, soil is half solid materials such as sand, silt, clay, nutrients, etc. The other half should be pore space. Half the pore space should be occupied by water and half by air.

“Before tile is installed, evaluate the soil structure,” Hemenway advises. “Another issue in rolling landscape is the movement of water from where it falls. It may appear that there’s excess water in a field’s low spots when what’s really happening is loss of water on hills and ridges. Tiling can cost $1,000 per acre or more and, depending on the reason for water ponding, that water may not even reach the tile.”

Since nutrients also move off a field when water leaves, effective water management can significantly impact an operation’s bottom line, Hemenway says.

“In an Ames, Iowa, study, researchers found as much as 30 pounds of nitrogen per acre was lost through their tile lines each year,” Hemenway says. “Priced at around $15 per acre, that can really add up. Water quality also becomes an issue.”

Some saline areas may also contain excessive levels of sodium, causing them to react as saline-sodic. Sodium causes clay and soil organic matter to disperse, limiting or completely stopping water movement through the soil profile. Tiling these areas could cause a loss of calcium and result in a gradual increase of sodium, which in turn increases the sodium absorption ratio. This process, known as sodification, can result in yield reductions that can be difficult, if not impossible, to recover from.

“Those soil conditions could be irreversible,” Hemenway says. “We have some saline-sodic sites in the Jim River Valley, so test your soils before you start, as pulling water out of them could further damage soil structure.”

No-till improves soil structure, but each no-till site has its own characteristics. Improved water infiltration is typically seen in a no-till system. However, infiltration rates can vary with the crop rotation. At a site with a diverse crop rotation, water from a heavy rain shower may soak into the ground in as little as two minutes. In a no-till field without a diverse rotation, it may take 15 minutes for the water to disappear.

If you see water standing for 15 minutes, you may conclude that the soil is too wet when, in fact, that’s not the case at all.

In a conventionally tilled field, it may take up to eight hours for 1 inch of water to infiltrate into the soil. During that time, excessive runoff, erosion, nutrient loss and water pollution may all occur.

“For decades, tillage was seen as a beneficial farming practice,” Hemenway says. “Now we see the damage it causes. Somehow we need to come around to a different approach to crop production.”

Sorenson writes from Yankton, S.D.

See "How he stopped saline soil losses"