Richard Taylor, Extension Agronomist; rtaylor@udel.edu
With a week gone in April already, many growers are anxious to begin planting corn. The long range forecast promises at least a few days of warmer temperatures in the coming week. Along with the threat of rain later next week, this will certainly encourage corn producers to begin planting their fields as soon as possible.
One thing growers need to keep in mind is that soil temperature lags air temperatures, sometimes to a large degree. Corn requires that the soil temperature be above 50°F for germination to proceed and growth to occur.
Another complicating factor is tillage. Soil in a no-till system tends to be wetter and cooler than that from a system incorporating some tillage. This translates into the need to keep seeding depth on no-till and early planted fields more shallow than for tilled and later planted fields. I would suggest maintaining a 1.25 to 1.5 inch seeding depth until soil temperature at a 3-inch depth begins to be consistently above 55 to 60°F.
Dr. Bob Nielsen at Purdue University has demonstrated that corn planted very early on cold soils where the temperature rises very slowly over a several week period takes as much as three weeks or more to emerge. Lengthy emergence periods lead to uneven emergence and large developmental differences between the early emerging plants and the later emerging plants. This uneven emergence can cause yield losses of 20 or more bushels per acre.
Once warm weather remains around long enough to significantly increase soil temperature, planting depth can be adjusted deeper to be sure the seed is placed in moist soil and is consistently deep enough for good root development. Wet fields and no-till fields will be the last ones in which to lower the planting depth to normal levels.