Extension Agronomy has been continually monitoring the roller coaster ride of soil and air temperatures during April and May. For this week (May 7-13), the minimum soil temperature at 2 inches ranged from 45 °F in north central Kansas to 65 °F in the southwest. Temperatures at the 4-inch depth are not much different. Weekly average soil temperatures at the 4-inch depth ranged from 53 °F in the northeast to 77 °F in southwest Kansas (Figure 1).
Figure 1. Minimum soil temperatures at 2-inch (upper panel) and 4-inch (lower panel) soil depth for the week ending May 13, 2020.
Figure 2. Soil temperatures and air temperature patterns at various Mesonet stations for the week ending May 13, 2020.
Chilling injury to seeds and emerged plants
Cold temperatures can result in injury to the germinating seed as it is absorbing moisture – a problem called imbibitional chilling injury. Damage to germinating seeds can occur when soil temperatures remain at or below 50 °F after planting.
Soil temperatures at the 4-inch depth during the first 24-72 hours after planting are critical. It is during this window that the kernels imbibe water and begin the germination process. Kernels naturally swell when hydrating – taking in water. Injury symptoms may include swollen kernels that fail to germinate or aborted growth of the radicle and/or coleoptile after germination has begun.
Chilling injury to seedlings can result in:
Chilled seedlings may also be more sensitive to herbicides and seedling blights.
Before making any decisions, fields should be scouted 4-7 days after the cold occurred since the extent of the damage and potential for new growth will be evident during this time.
Comparing chilling injury for soybeans versus corn, emerged soybeans are more susceptible since their growing point is above the soil surface. However, soybeans plants can recovery from freezing injury from growth in the potential growing points from the main shoot or from the two axillary buds.
Warmer weather is expected in the next week. The rapid switch in temperatures will increase stress, particularly in drier areas of the state. Stay tuned!
Ignacio Ciampitti, Crop Production and Cropping Systems Specialist
Mary Knapp, Weather Data Library