Research shows that tiling farm land also helps control runoff

By W. Doral Kemper

----

EDITOR'S NOTE:  For more information on the research this article was based on, visit the Journal of Soil and Water Conservation online, at this link to the article: http://www.jswconline.org/content/67/1/11A.extract 

The U.S. Midwest is one of the most productive areas on Earth because the average annual rainfall is close to the water requirements of most grain crops. When there is higher than average rainfall, water accumulates in the soil, raising water tables near the surface and reducing growth of roots, which need oxygen to thrive.

Decades ago, owners of the fertile bottom lands dug ditches to drain the excess water away and increase productivity of their land. Some of these lowlanders brought tile drainage technology from Holland and made fired clay, or concrete tiles, which they placed in tile lines 3 or 4 feet deep to drain water from the soil. This drainage lowered the water table, but required a lot of labor and material.

Development of perforated polyethylene tubing and laser-guided equipment that can slip this into the ground, precisely where needed, has reduced costs of tile drainage to a small fraction of its costs compared to 70 years ago.

The shift from moldboard plows to chisels and no-till has enabled farmers to leave more crop residue on the surface, which also has increased infiltration and decreased evaporation and erosion. These changes have been generally beneficial to Midwest soils and crop production.

However, leaving more water in the soils has increased the water table heights. In areas where most of the runoff 70 years ago was a result of rainfall rates exceeding infiltration rates, most of the runoff is now a result of high water tables, leaving little room for storage of water in the soil. Thus, only an inch or so of rain often initiates runoff. On these lands with high water tables and rapid infiltration rates, tile drainage can substantially increase the water detention capacity of the soil.

A colleague and I measured the outflow of six tile drainage systems serving known acreages and found that tile drainage increased the stormwater detention capacity of those fields by an average amount of about 3 inches deep across. The original purpose of installing the tile was to increase crop production and the efficiency of farm operations. However, we also concluded that the tile produces a byproduct of considerable value to the community - i.e., increased stormwater detention capacity.

One way of assessing the value of stormwater detention capacity is to compare the cost of stormwater detention in reservoirs commonly constructed for this purpose. Of several such reservoirs built or under construction in Winnebago County, Wis., the lowest cost was 60 cents per cubic foot of detention capacity.

The total cost of tile drainage is about $1,000 per acre, or about 10 cents per cubic foot if all of this cost is ascribed to stormwater detention.

We have recommended to the city of Oshkosh - which needs more detention capacity in its Sawyer Creek watershed - that instead of building reservoirs and taking land by eminent domain, they offer tile to farmers in that watershed. With the farmers paying the $700 per acre installation cost, and the city paying $300 per acre for the tile, the cost to the city of increased stormwater detention capacity would be 3 cents per cubic foot.

The city's engineers have agreed to consider putting this project in the 2013 budget plan and farmers are signing up to participate.

W. Doral Kemper of Oshkosh, Wis., has 50 years' experience as a soil scientist. He consults with the Pakistan Council for Research on Water Resources and conducts research on water management with farmers in Wisconsin. Comments: ddoralida@aol.com