rows of corn
KEEP IT GREEN: Subirrigation can help put water back into the field when corn needs it by sending water through tile lines.

Subirrigation still exists but hasn’t caught on

Corn Illustrated: Study shows using subirrigation can increase corn yield over the long haul.

Subirrigation is not a new concept. Stories about farmers using subirrigation to supply water to crops in the driest part of the summer appeared in farm publications 30 years ago, and occasionally since then. A USDA researcher who was one of the first to hit 100 bushels of soybeans per acre in research plots some three decades ago in Ohio included subirrigation as part of the process to produce high yields.

Back then the researcher explained that the concept was simple: Use the same tile lines that remove drainage water in the spring to put water back into the soil during the dry months. The catch, of course, is that it requires a catch basin or pond of some sort to hold and supply water when crops need it in the summer. That’s likely one reason the adoption of this technology has a hard time getting off the ground.

Test results
Beck’s has included subirrigation in corn in Practical Farm Research tests near Atlanta, Ind., for the past seven years. “We’ve proven that it works at that site, so we’re not continuing the study there,” says Alexandra Knight, with Beck’s PFR. “However, we’re continuing to look at it at our PFR site near Effingham, Ill.”

The seven-year average advantage in corn yield at the Indiana location is 22.5 bushels per acre, according to Beck’s 2018 plot trial book. At $3.50 corn, that’s $78.75 average extra gross income per acre per year.

If you only look at 2017, however, subirrigation didn’t see better results than just tile drainage. Knight says that’s because in 2017, with a wet spring and plenty of moisture available during the summer from rain events, the advantage was for getting water out of the ground in the spring through tile drainage. There wasn’t necessarily an advantage for putting water back into silt-loam soils last year.

During the past two years, when data from both sites is combined, the top yield advantage came from subirrigation using moisture sensors to determine when to allow water back into the tile system. Contour drainage alone also produced slightly better yields than manual subirrigation over the past two years.

Drainage matters
Jonathan Perkins, a Beck’s agronomist and PFR location lead, says contour drainage is important at the PFR site in Illinois. Located near Interstate 70 in south-central Illinois, wet soils in the spring are often an issue there.

Contour tiling involves following the slope with tile lines rather than installing a pattern-tiling system where every tile line runs straight, Perkins explains. The tile contractor who designed the system determines how close tile lines need to be in various locations in the field based on slope and soil type. At some points, tile lines may only be 15 feet apart, Perkins says.

The result is a system that provides good drainage so farmers can get in the field sooner in the spring. In drier years, being able to add water back through tile lines helps, he adds. In years like 2017, when rain continues throughout the growing season, there is minimal advantage, if any, for adding water back during the summer.

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