The populations of 30,000 plants per acre or more seemed fine in the Corn Illustrated plots of the past two years- until it turned very dry. In '07 it happened early and stayed that way. In '08 it was wet early, but turned dry alter on. Both years led to less than top yields, with '07 being by far the worst.
Soils for some of the plots were underlain with gravel at three feet. "You really see the signs of drought stress quickly on these types of soils," says Dave Nanda, president of Bird Hybrids, Tiffin, Ohio and former consultant for Corn Illustrated. The plots were sponsored by Farm Progress Companies.
This year the signs of drought stress may mean more than your soils have gravel at three feet, Nanda notes. If it turns dry here at mid-season, drought stress is possible, even on dark, level, naturally wet soils. The biggest culprit this year may be soil compaction. Just to get a crop in the ground, many people had to work soils wet. Either big tractor tires created soil compaction, or opener disks, creating sidewall compaction in the seed trench, or both.
If it keeps raining, these effects may not show up this year, Nanda observes. But if something else stresses plants, such as dry weather and a lack of abundant moisture where the roots can get to it, then soil compaction could become important. It's even possible that it could reduce crop yields in some fields.
Sometimes the stress is just the population itself, Nanda adds. Obviously, 30,000 plants per acre on a soil underlain by gravel is too much in a dry year. What about someone growing corn literally in a sandbox, with near zero organic matter and no loam topsoil at all?
Eric Wappel finds himself in that situation. He farms with his dad and mom, Larry and Debbie, and brother, Larry Jr., in Starke County. Only some of their soils are sandy. But it's helped lead him to changing seeding rates on-the-go. He programs in rates for various soils in various parts of the field by creating a prescription map that when inserted into a computer in the tractor cab, directs the computer about how to control machines so that different rates of seed are dropped in different parts of the field.
If it turns dry and those sand hills are at 30,000 or more plants per acre, the stress will be horrific, Wappel notes. In fact, it may be difficult for plants to produce anything at all under that stress. But it's a certainly that the stress will reveal itself quickly on those kinds of soils, he observes.