Tile drains are pipes made of perforated plastic, burned clay, concrete, or similar material, buried about three feet below the surface of a field and at a slope designed to collect and carry excess water from the soil. In soils that tend hold a lot of water or have a water table that is close to the surface, drainage allows crops to be planted earlier in the spring and keeps water from pooling on the surface or saturating the root zone so much that the crops 'drown'.
The use of tile drains (and other drainage measures) have have allowed the North Central U.S. region, which has fertile soils that are often stay too wet and cold in the spring for most crops, to become one of the most productive agricultural areas in the world.
However, while enhanced drainage of cropland has produced higher yields economically, there are environmental costs. Large areas of wetlands have been lost and there is great concern over about the rapid, direct transport of excess nitrates and pesticides to surface waters. Most of the work at the Experimental Drainage Plots at SEPAC, as well as some of the projects at the Water Quality Field Station have focused on these concerns.