Farmers who planted corn after mid-May said they usually set it two inches deep. Some wondered if that was too deep, but reports say that it came up quickly and uniformly.
That's not a surprise to Jeff Phillips, the Tippecanoe County Extension ag educator who has helped coordinate plot trials for Indiana Prairie Farmer and Precision Planting over the past few years. For two years in a row, corn planted at the 4 inch deep – that's four full inches into the soil below the surface – emerged well and in about the same time as corn planted at 2- and 3-inch depths. The only caveat is that soils were warm. Their trial theory has still not been tested on very cool soils.
So if you're planting now, don't hesitate to go as deep as you want. The corn can push up through the soil and emerge. Going deeper guarantees that you access moisture, and the temperature at that level now is far over the 55 degrees F needed for corn to germinate.
What you don't want to do now is plant too shallow, and risk issues with the soil drying out. Phillips notes that in one year, the planting at one-inch depth had erratic emergence all year and wound up yielding about 20 bushels less than the other three planting depths. For that year in that location, that was a significant reduction in yield for planting too shallow. The differences in the other three depths were not significant.
In that year, the soil was dry at planting, and then it didn't rain for about a week. Phillips theorized that the corn planted one inch deep started to germinate, but some kernels didn't have enough moisture to finish the job. What was surprising was that depth, emergence ran about two growth stages behind the other planting depths all season long.