As a reader has pointed out, I should have used a better article to illustrate that field tiling is used for both drainage and sub-irrigation. I had downloaded several on the subject at the same time from agriculture.com.
It does not change the context of the post however. We have two systems for horticultural education, one for professionals and a dumbed down version for consumers. The use of the words sub-irrigation (professionals) and "self-watering" (consumers) is a prime indicator of this split.
Sub-irrigation is used productively in commercial agriculture in both greenhouses and fields. The same benefits of water conservation, higher productivity and labor savings are also available to individuals who use sub-irrigation. Why isn't this information widely publicized to all of us as consumers and amateur gardeners?
This controlled drainage system can also be used to subirrigate a field. By pumping water from a pond or well back into the buried pipes, water can be pushed back toward plant roots. “Our research in subirrigation mode used only 25% as much water as an overhead irrigation system would use,” says Nelson.
At the University of Missouri Greenley Memorial Research Center near Novelty in northeast Missouri, they've been testing a tile drainage system that controls the flow of water during the course of a season. This isn't like most tile drainage systems. With a gate at the discharge point, this system controls the flow of water rather than draining wide open year-round.
System managers can let water drain in the spring to dry out the soil for planting, then they can close a gate in the discharge pipe in the summer to back water up to the root zone of thirsty corn or soybeans. The gates can be opened again in the fall for harvest, then closed again in the winter to limit leaching and to conserve fertilizer.
“Our research and other research show up to a 75% reduction in the nitrate load in drain water with this type of managed drainage,” says Kelly Nelson, a research agronomist at the Greeley Center, who operates this drainage system. Read more...