The recent Shelby County Soils Judging contest sponsored by Shelby County Extension proved to be another dramatic illustration of how soils interacted with the drought and heat to make a huge difference in corn yields this year. The contest was held on a farm in western Shelby County.
The first hole was on an outwash plain coming up from a major waterway. It formed over sand and gravel, but the gravel was more than four feet deep, too deep to affect corn roots. Instead, it's a poorly drained soil, the same soil that produced decent corn in the 2012 Crop Watch field. Corn growing near the hole not yet harvested was about normal height. A rough estimate would place yields around 100 bushels per acre.
On the other end of the spectrum, the length of the field farther back on the uplands, corn was very short in one spot. A quick look at barren stalks and nubbin ears formed a guess of around 20 bushels per acre.
"I wanted to find out why the corn looked so poor there, so we dug it as a pit," says Scott Gabbard, Shelby County Extension ag educator. He's also a former soil judger for Gary Steinhardt at Purdue University. Jerry Shively, a retired soil scientist, also assisted in judging the contest.
The soil on a position with no slope but a bit of a bubble, known as a swell, would be expected to somewhat poorly drained, and it was. However, the problem was a few inches deeper. This was a soil formed by glacial till. In this case the till was deposited in tight layers, referred to as dense till. You could argue about exactly where it started, from 18 to 25 inches, but that's a high position for dense till to start. Soil scientists doing septic system appraisals want to know about it, because water is slow to percolate through dense till.
Gabbard concluded it's why the crop looked so short and poor at that location. The plants only had 15 to 25 inches to work with. The rest of the soil, once it dried out this year, was so hard that roots would have found it very difficult to penetrate. In effect, there is about 20 inches of water-holding capacity. When corn was using up water at alarming rates in the heat of early July and no rain fell, it was simply too much to keep the crop supplied and functioning properly.