Take the following info for what it is worth. I have been trying to figure out the affect of frost remaining in the ground on the soil temperature at the 2 inch depth where the corn seed is placed. The fall worked soybean in the charts was soybean stubble that was worked last fall. With all the wind we had over the winter there was not much of any snow cover on it. I checked the frost depth this spring and was at about 57 inches deep.
 The 3x3 bare spot and old rye residue treatments were close to standing spring wheat stubble so they had snow cover most of the winter and i calculated the depth of the frost using soil temps and came up with 33-36 inches deep.
The frost had left those two treatments earlier, while the frost line was 32 inches down from the surface in fall worked on 4/25.
 Notice that durning  the late afternoon and overnight hours the fall worked temps drop below the other two treatments. I am thinking that those temps might have a bad influence, if low enough, on the corn  seedling.

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