If someone tells you that having cover crops on the surface, either burned down or still growing, will lower the soil temperature, you can tell them they're right … sort of. It depends upon when you check.
Recently, Larry Huffmeyer, a Syngenta rep and farmer in Ripley County, checked soil temperature in various situations on his farm. He made the checks in mid-May. The lowest soil temperature at the four-inch depth at noon was 65 degrees F in corn already emerging. The crimson clover cover crop was burned off after planting, and was still covering a good part of the surface.
Agronomists say corn normally needs 55 degrees minimum to germinate and emerge. At 65 degrees there was plenty of warmth for germination.
The temperature was the highest, above 70 degrees, where a cover crop of wheat was burned down in very early April. The field was not yet planted, and the cover had not been disturbed. The cover was so broken down that it wasn't immediately obvious that a cover crop had been planted there.
The temperature fell in between those marks in two other situations. One of them was standing rye in an area where the rye was not burned down. It was at least three feet tall and flowering. Huffmeyer burnt rye down at about knee-high, but left this patch to protect a waterway.
The soil temperature under the rye cover burned down several weeks ago was also between the other two measurements. There was definitely more cover left on the soil in this case than in the field where wheat was burned down early. However, the decaying rye was not heavy enough to form a mat which would keep the soil from drying out and getting ready for planting.
For more, download our free report, Cover Crops: Best Management Practices.