A Survey Of Corn Extension Agronomists On
Soil Temperature Requirements For Planting Corn

April 23, 1998  5(6):37

Joe Lauer, Corn Agronomist

Recently, Dr. Richard Taylor at the University of Delaware conducted a limited survey among U.S. university corn extension agronomists on soil temperature requirements for planting corn. Soil temperature recommendations were somewhat consistent, but approaches for determining soil temperature ranged all over the spectrum. Most agronomists felt that soil temperatures should be between 50 and 55 degrees for planting corn. Large discrepancies were noted as to the time of day and soil depth at which soil temperature should be determined. Some do not consider soil temperature and plant by the calendar.

Table 1. Survey of U.S. university corn agronomists on soil temperature recommendations for planting corn.
Soil Temperature Recommendation For Planting Corn	Percent
50 degrees at any time (increase planting rate by 2,000 kernels per acre); check the forecast to be sure that for the next 3 to 5 days temperatures would be 50 or greater	18
50 degrees at 7 to 8 am	18
55 degrees at 1 pm on a clear day	9
55 degrees at 1 pm at 4 inch depth or 50 degrees at 7 am at 2 inch depth	9
55 degrees at 10 am for several days	9
55 degrees at 7 am for 3 consecutive days	9
Calendar date	27
Richard Taylor, University of Delaware, 1998

Regardless of soil temperature, be sure the soil conditions will support equipment without causing severe compaction problems. In Wisconsin, the optimum planting date for corn is between May 1 (south) and May 7 (north). Little change in yield is observed between April 20 and May 12 in southern and May 15 in northern Wisconsin.

Prior to April 20, soil temperature may be useful, but most Wisconsin soils are usually too cold for corn planting. If you want to plant earlier than April 20 use the following soil temperature guidelines:

1. Measure soil temperature at corn planting depth. If the early morning soil temperature is above 50 degrees, then consider planting. Check the forecast to be sure that for the next 3 to 5 days temperatures would be 50 degrees or greater
2. Measure soil temperature in the same type of soil as you will plant in.
3. Finally, measure soil temperature in the same type of tillage, crop residue, or cover crop system.
4. Increase seeding rate by 2,000 kernels per acre when planting very early in cold and wet soils due to erratic stands typically observed under these conditions. Stand may not be a problem if soil is cool and dry.

Of course, the biggest problem anytime you go real early is knowing exactly what the weather will eventually turn out to be. Typically only about half of the days during late April and early May allow fieldwork to occur. You must weigh your planting workload and what you think the weather will be to begin corn planting. When planting is delayed intentionally, there's no guarantee that the weather won't delay it another week, or perhaps more.