Soil temperature conditions for uniform corn germination and emergence
Corn planting when soil temperature and moisture conditions are most favorable is critical to uniform emergence and stand establishment.
Soil temperature together with soil moisture conditions determine the ideal planting time for many Michigan crops. The minimum threshold temperature for corn seed germination is 50 degrees Fahrenheit in the seed zone. Corn will germinate and emerge slowly and unevenly when soil temperatures are less than 50 F. Thermal time from planting to emergence is approximately 115 growing degree days (GDD) based on air temperature or about 119 GDD based on soil temperature using the modified growing degree formula. Under ideal soil temperature and moisture conditions, corn will emerge in seven to 10 days. Uneven soil temperatures in the seed zone can be caused by variable soil texture, color, drainage, and surface residue cover and seeding depth. Dark-colored soils will warm more quickly than light-colored soils.
Typically, soil takes a longer time than air to warm up. A quick check at the Michigan State University Enviro-weather data from the Leslie, Michigan Enviro-weather station shows the minimum soil temperatures during the past 10 days have been hovering around 45 F, indicating that soils are not quite ready for planting corn, but are getting closer (Fig. 1). The maximum soil temperature has consistently reached 50 F or above during the same period. The average soil temperature for the most part is staying between 45 F and 50 F. MSU Enviro-weather is an online weather service provided for free. Michigan State University Extension encourages farmers to use this tool as a best practice for informed crop management decisions.
Figure 1. Maximum, minimum and average soil temperatures at a 2-inch depth in Leslie, Michigan, April 1-26, 2014
One of the many lessons learned from the famous 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 weather and higher than normal GDD accumulations 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. Previous field research has shown that the optimum corn planting period in Michigan is the beginning to middle of May. The soil temperature data suggests this optimum corn planting period may hold true, if not slightly delayed, in 2014.