For the week of May 1 to May 6, the average soil temperature at 2 inches ranged from 58 °F in north central Kansas to 75 °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 59 °F in the northeast to 71 °F in south central Kansas (Figure 1).
Figure 1. Average soil temperatures at 2-inch (upper panel) and 4-inch (lower panel) soil depth for the week of May 1 - 7, 2020. Map data from Kansas Mesonet.
Air temperatures are projected to go below 40°F for May 8-10 (Fig. 2). Minimum temperatures across the state will drop to 32°F on Sunday morning (May 10) for the northwest region and less than 35°F for north central area of the state (Fig. 2). This will produce a problem for the recently planted corn and soybean crops with soil temperatures declining in the next coming days following air temperature changes.
Figure 2. Minimum air temperatures for the next days, Saturday, Sunday, and Monday (May 9-11, 2020). Source: NOAA
With morning lows on May 8 in the 30s in the northwest and in the mid-40s across the rest of the state, minimum 2-inch soil temperatures also dropped (Figure 3). Dry, bare soils will cool more rapidly than moist soils, and the temperatures will warm more rapidly as well.
Figure 3. Minimum air temperature (upper panel) and minimum 2-inch soil temperature (lower panel) for May 8, 2020. Map data from Kansas Mesonet.
Chilling injury to seeds
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. If the cell tissues of the kernel are too cold, they become less elastic and may rupture during the swelling process, resulting in “leaky” cells. 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 can also occur following germination as the seedlings enter the emergence process. Chilling injury to seedlings can result in:
- Reduced plant metabolism and vigor, potentially causing stunting or death of the seminal roots
- Deformed elongation (“corkscrewing”) of the mesocotyl
- Leaf burn (Figure 3)
- Delayed or complete failure of emergence, often leafing out underground
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.
The biggest risks are likely to be in the northwest, where temperatures are expected to be the coldest and soils are dry. More information about the potential impacts on low temperatures will be in upcoming issues of the Agronomy eUpdate. Stay tuned!
Figure 4. Leaf burn from freeze damage early after corn emergence. Photo by Ignacio Ciampitti, K-State Research and Extension.
Ignacio Ciampitti, Crop Production and Cropping Systems Specialist
ciampitti@ksu.edu
Mary Knapp, Weather Data Library
mknapp@ksu.edu