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Controlled tile drainage

02/16/2012 @ 3:17pm

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 Greenley Center, who operates this drainage system.

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.

There are fewer moving parts than pivot irrigation, and the water doesn't have to be pressurized to get it on fields, another cost savings. For the claypan soil, researchers needed lateral lines on about 20-foot centers to subirrigate, while in a drainage-only system, they could usually get by with fewer laterals spaced farther apart.

Of course, the yield payoff for managed drainage combined with subirrigation is going to depend on the weather. In a wet year, drainage alone will give a big bang. In a dry year, the payoff will come from subirrigation. Some years, there's a combination effect.

Nelson now has yield data for 10 years of work on this project. “Over those 10 years, drainage alone gave a 22-bushel corn yield response,” he says. “In wet summers only, drainage alone will get up to a 40-bushel increase in corn yields.

“Add in the subirrigation, and we've seen up to a 60-bushel-average yield increase. In the very dry summer of 2005, we got an 83-bushel yield increase from drainage and subirrigation. That was essentially a doubling of yields,” Nelson says.

In one five-year comparison of overhead irrigation to subirrigation, the overhead system gave about 10 more bushels an acre on average (195 vs. 185). Overhead irrigation, however, took four times the volume of water.

As for 2011 crops, Nelson says yield results will confirm the long-term trends. Subsurface drainage alone will get a 20% yield response; combine that with subsurface irrigation and get a 40% yield improvement over the long term.

“Drainage in the spring gives a drier seedbed and about a three-day earlier planting date, and an additional advantage in the form of a better stand,” he says. “Irrigation then helps fill the crop out when it gets dry in July and August.

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