By George Silva, Michigan State University Extension
Corn planting when soil temperature and moisture conditions are most favorable is critical to uniform emergence and stand establishment.
Soil temperature along with soil moisture conditions determine the ideal planting time for many Michigan crops. The minimum threshold temperature for corn seed germination is roughly 50 degrees Fahrenheit in the seed zone (purple/straight line in the two figures below). When the soil temperature drops much below 50 F, there is potential for chilling injury and delayed germination. Under ideal soil temperature and moisture conditions, corn will emerge in seven to 10 days. Uneven soil temperature in the seed zone can be caused by variable soil texture, color, drainage and surface residue cover and seeding depth. Dark soils will warm quicker than light soils. Typically, soil takes a longer time than air to warm up.
A quick check of the April 2016 soil temperature data at a 2-inch depth from Michigan State University’s Charlotte Enviro-weather station (Eaton County) and Leslie Enviro-weather station (Ingham County) shows the minimum soil temperatures during the past seven days has been above 45 F and may rapidly approach 50 F, indicating soils may be ready for corn planting in a few days (see figures below). The maximum soil temperature has consistently reached above 50 F during the same period. The average soil temperature has also stayed above 50 F. MSU‘s Enviro-weather is an online weather service provided free to Michigan farmers. MSU Extension encourages farmers to use this tool as a best practice for informed crop management decisions.
One of the many lessons learned from the infamous 2012 season was the importance of waiting for the soil to warm up to the right temperature before planting corn. In 2012, the abnormal, early warm March and April weather enticed some farmers to plant corn in early April, disregarding the soil temperature. This resulted in chilling injury to seeds and uneven emergence and stand loss.
While soil temperature is an important determinant factor for early planting, soil moisture conditions also needs to be right. Planting on soils that are too wet will produce soil compaction and create conditions that make it harder to plant and close the seed furrow properly. Also, be prepared to spend as long as it takes on the opening day of planting to get the equipment adjusted property. This may take some digging behind the planter to check if the planting depth and spacing is right.
Previous field research has shown that the optimum corn planting period in Michigan is the beginning of May to middle of May. The soil temperature data in 2016 suggests this optimum corn planting period may hold true, although optimum conditions could be slightly early this year.
Figure 1. Soil temperature for April 2016 in Charlotte, Michigan.
Figure 2. Soil temperature for April 2016 in Leslie, Michigan.