The plot that Indiana Prairie Farmer and the Tippecanoe County Extension Service and Throckmorton Research Center cooperated on in 2013 compared downforce settings at two different planting depths. Because the plot couldn't be planted until early June, the crop shifted from corn to soybeans. Typically corn is thought to be more sensitive to downforce effects. However, while results weren't significant, there was some indication that downforce affected soybean planting as well.
The planter was equipped with Precision Planting's Air Force unit which adjusts planter units as a group to meet the specified downforce level. Within a one-inch and two-inch planting depth, four downforce pressures were specified. The system then met those specifications.
The two depths were not done side-by-side. Instead, one block contained all the downforce replications on that depth. The next block contained the downforce replications at the other depth.
Within a given depth, the heaviest downforce produced the highest yield both times, notes Jeff Phillips, Tippecanoe County Extension ag educator who coordinated the plot. However, even in the deeper depth, the results were not significantly different at 0.1 level of least significant difference. At the 0.2 level, which allows for more experimental error wiggle room, the heaviest downforce was likely significantly higher yielding than the lowest downforce, Phillips says.
"It appears that this year planting into very dry soil, the deeper downforce setting helped the seed contact moisture and helped on emergence," he says. "It's important to remember that this was one test in one year."
There was a couple of tenths of rain the day before planting, and about four tenths a couple of days after planting – otherwise soil was very dry, Phillips notes. The rain falling after planting may have helped the shallow planted beans, especially at the lightest downforce setting, he speculates.
The main observation was that downforce can make a difference, even in soybeans, at least in very dry soil conditions, the extension educator concludes.