By Jeff Coulter and David Nicolai, University of Minnesota Extension

With wet conditions and cool soils, corn planting is just starting in southern Minnesota. Long-term research data from the University of Minnesota indicate that the optimum planting date for corn in Minnesota is during the last week of April and the first week of May, with only an 8 percent yield reduction when planting is delayed from April 30 to May 15. In addition to higher yield, earlier planting can normally result in earlier maturity, thereby allowing more calendar time for drying of grain prior to harvest and for fall tillage. The average relationship between planting date and corn yield in Minnesota is explained in a past issue of Minnesota Crop eNews, available at http://www.extension.umn.edu/cropenews/2003/03mncn10.htm.

While timely planting is important, the advantages of an earlier planting date can be lost if tillage and planting operations occur when the soil is too wet. Sidewall smearing can occur as planter disk openers cut through wet soil, resulting in compacted soil around the seed that is difficult for seedling roots to penetrate. Seed furrows can also open up after the soil dries following wet conditions at planting. In addition, soil compaction from heavy machinery on wet soil can reduce yield this year and in the future.

Planting into cool and wet soils also increases the potential for corn seedling diseases. To reduce the prevalence of seedling diseases, use high quality, fungicide-treated seed. However, corn seed treatments are usually effective for only two to three weeks after planting. While soil temperatures of at least 50 degrees are needed for corn germination, soil temperature in early May can generally be ignored as a factor, and planting should begin as soon as the soil is dry enough.

Keep in mind that while higher corn yields are associated with earlier planting, planting date is just one of many factors that determine yield. Avoid “mudding the seed in” just to get the crop planted early. Corn growers should have patience and take time to make sure that planting is done right.

• Avoid working wet soil and creating cloddy seedbeds, which can inhibit the elongating mesocotyl of young corn plants.
• Avoid excessive tillage prior to planting (possible soil compaction and surface crusting), especially if significant rainfall is forecast before emergence.
• Avoiding “rootless” corn which can be caused by extremely shallow seeding depths (shallower than 1- to 1 1/2-inches) that result in nodal root initiation beginning near the soil surface rather than at the usual 3/4-inch depth. A planting depth of 1 1/2- to 2- inches is ideal in most situations.

While the effect of delayed planting on corn yield has been documented over the years in Minnesota, keep in mind that these figures are averages. In some years with good summer weather and extended fall growing conditions, good yields can be expected even with delayed planting.

(Jeff Coulter is a corn specialist with University of Minnesota Extension and David Nicolai is a University of Minnesota Extension educator in crops management.)