Ground temp reading

Planters made some progress across portions of Iowa in recent weeks, but soil temperatures quickly fell back below 50°. What does this mean for corn and soybean already planted?

Imbibitional chilling occurs when there is a drastic change in the water temperature after planting, according to Mark Licht, Iowa State University Extension cropping systems specialist. The critical time for this to occur is within 24 hours of planting. Cold injury is when there is a change in the soil temperature after the seed has imbibed water.

The effects of imbibitional chilling and cold injury are ultimately the same — reduced stand establishment and seedling vigor, Licht said in an Extension news release. Severe imbibitional chilling can result in seed death, “corkscrewing” of the mesocotyl and leafing out underground as well as surviving seedlings having reduced seedling vigor.

At this point, there is nothing that can be done for corn and soybean that have already been planted. If you are curious of the impact that this temperature change made, conduct stand assessments once emergence occurs.

Determine what the plant population is. Simply count the number of plants emerged in 1/1000th of an acre (17.5 feet for 30-inch rows).

Identify how uniform emergence is. Look to see if all plants are evenly spaced within the row. Pay attention to how uniform plant height is to determine how uniform the emergence rate was.

Evaluate why plants are missing or delayed. Dig along the furrow to find the presence of a seed. If there is no seed, it is likely a planter performance issue. If there is a seed that has died, corkscrewed or has a leaf out underground, there is a good likelihood of injury from the cold temperatures. Plants that emerge days later may be the result of deeper seed depth placement or reduced seedling vigor.

If you have reduced stand or uneven emergence here are a couple of resources to guide next steps: