With the colder than normal spring and now generally wet conditions across Michigan, growers may want to consider both the current soil temperature and the two- to three-day temperature and precipitation outlook before planting.
Michigan State University Extension soybean educator Mike Staton often references a greenhouse demonstration conducted by Ontario Ministry of Agriculture and Food soybean researcher Horst Bohner. Bohner’s work clearly demonstrated the impact that the temperature of the initial soil moisture imbibed by soybean seeds has on germination and emergence. The soybeans were subjected to three soil conditions immediately after planting:
Warm conditions (77 degrees Fahrenheit) for 17 days
Cold soil (45 F) for 20 hours and then warm soil for 17 days
Warm soil followed by cold conditions (eight hours of warm then cold for four days and warm for 13 days) immediately after planting
Soybean seedling vigor, growth and development were greatly impacted when the temperature of the soil moisture first taken up by the seed was cold as compared to seeds that were exposed to warm soil and warm soil followed by cold conditions. The temperature of the soil moisture that first hits the seed is important. Overly dry seed and seed with thin or split seed coats is more susceptible to imbibitional injury. Soybean producers should know the quality of each seed lot and plant the highest quality seed first and the poorest quality seed last
Cold soil moisture temperatures can also cause corn seedling injury. Purdue University corn agronomist Robert Nielsen reports that while it is not clear how low soil temperatures need to be for imbibitional chilling or subsequent chilling injury to occur, temperatures below 50 F can be risky. Some sources indicate the threshold soil temperature for injury is below 50 F, while others suggest the threshold soil temperature to be 41 F. Injury occurs when the cell tissues of the kernel are too cold; tissues become less elastic and may rupture during the seed swelling process. Damage usually occurs during the initial 24 to 36 hours after planting under normal soil moisture conditions. Symptoms include failure to germinate, slow development of root and coleoptile growth following initial germination.
To reduce risk from chilling injury, growers should look at the soil temperatures at the time of planting in combination with a favorable two- to three-day temperature forecast. With adequate soil moisture, the first 24 to 36 hours may be the most critical to help prevent chilling injury from occurring to the developing seedling. The MSU Enviro-Weather stations in your area can give you an idea of the maximum and minimum soil temperature in your area. An inexpensive probe thermometer can be a good investment. Soil temperatures are often coolest around 7-8 a.m. You can visit the Climate Prediction Center’s 6-10 day outlook in addition to your local forecast to review expected temperature and precipitation trends.