Imbibitional chilling occurs when there is a drastic change in the water temperature during imbibition. This occurs when soybean seed imbibes very cold water, under 45oF, in the first 6 to 24 hours after planting. Imbibitional chilling is often associated with a cold front that brings not only colder temperatures but also cold rainfall within 24 hours of planting. Cold Injury is when there is a change in the soil temperature after the seed has imbibed water beyond 24 hours after planting. Seed, in the osmotic phase of water uptake, is more cold-tolerant to temperatures as low as 35 to 40oF. However, this will delay germination and emergence putting the seedling at greater risk of soil-borne pathogen infection and insect feeding.
The effects of imbibitional chilling and cold injury are ultimately the same, reduced stand establishment and seedling vigor. Severe imbibitional chilling can result in seed death, ‘corkscrewing’ of the corn mesocotyl, corn leafing out underground, dead tissue on the exterior of the soybean cotyledons, uneven emergence, as well as surviving seedlings having reduced seedling vigor. Cold injury is typically less severe than imbibitional chilling. Regardless, the impact of a temperature drop is dependent on how big the temperature drop is, how long cold temperatures persist, and what the seed quality was.
Reduce the potential for imbibitional chilling and cold injury by utilizing these management practices:
- Look for seed cultivars that have better early season vigor or cold tolerance.
- Avoid planting seed having low initial seed moisture levels.
- Avoid planting when a cold rain is forecasted within the next 24 hours after planting.
- Plant high-quality seed having intact seed coats that are free of wrinkles or cracks.
- Plant in the early afternoon to allow soils to warm up; ideally 50oF and rising.
- Plant at a 1.5- to-2.0-inch depth to buffer soil temperature swings following planting.
- Plant into moist but not saturated soils; imbibition can occur without injury if soils are cooler (>45oF) if the soil is moist already.
- Plant seed with appropriate seed treatments for the insect and disease pests associated with cool soil temperatures.
If suspected imbibitional chilling injury or cold injury has occurred, conduct stand assessments to identify severity of the injury.