Corn requires favorable soil temperature for uniform germination and emergence
Planting corn when soil temperature and moisture conditions are most favorable is critical to uniform emergence and early establishment.
Soil temperature is an important factor in seed germination and emergence. Together with soil moisture, the temperature determines the ideal planting time for many Michigan crops. The minimum threshold temperature for corn seed germination is 50 degrees F in the seed zone. Corn will germinate and emerge slowly and unevenly when soil temperatures are less than 50 degrees F. Thermal time from planting to emergence is approximately 115 growing degree days (GDDs) based on air temperature or about 119 GDDs based on soil temperature using the modified growing degree formula (Nielsen, 2008). Under ideal soil temperature and moisture conditions corn will emerge in 7 to 10 days. Uneven soil temperature in the seed zone can be caused by variable soil texture, soil color, soil drainage, surface residue cover and seeding depth. Dark-colored soils will typically warm more quickly than light-colored soils.
Monitoring soil temperature on the farm or at the nearest weather station will provide useful information for planning planting dates. Typically soil takes a longer time than air to warm up. A quick check of the Enviro-weather weather data from Leslie, Mich., shows the minimum soil temperatures at 2 inch depth during the past 7 weeks have hovered around 32 degrees F indicating that soils throughout Michigan remain cold (Figure 1). advises the use of Enviro-weather as a best practice for farmers. This on-line weather service is provided free to Michigan farmers in 2013.
One of the many lessons learned from the 2012 season was the importance of waiting for the soil to warm up to the right temperature before planting corn. The abnormal, early warm weather in March in 2012 and higher than normal growing degree 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 research has shown that the optimum corn planting period in Michigan is the beginning to middle of May, when soil temperature and moisture conditions generally becomes most favorable.