In making the decision of the optimal planting date, producers should consider soil temperatures rather than just calendar dates. Air temperatures across Kansas cooled these past days.
For the week of April 4-10, average weekly soil temperatures at 2 inches among crop reporting districts ranged from 42 oF (northern locations) to 60 oF (southern locations) (Figure 1). For example, in the northeast region, soil temperatures were around 44 oF; while in the southwest region, soil temperatures varied from 46 to 60 oF. Soil temperatures were around 43-48 oF for the northwest region (Figure 1).
Figure 1. Average soil temperatures at 2-inch soil depth for the week of April 4 - 10, 2020. (http://mesonet.k-state.edu/)
Lowest soil temperatures were around 34-38 oF for the northwest region, 40 oF for the northeast, between 36-48 oF for the southwest, and around 47 oF for the southeast region (Figure 2).
Figure 2. Minimum soil temperatures at 2-inch soil depth for the week of April 4 - 10, 2020. (http://mesonet.k-state.edu/)
Projections for the coming weeks show a moderate risk for next week with a slight risk of hazardous temperatures for the week after (Figure 3).
Figure 3. Risk of hazardous temperatures for the next coming weeks, April 17 to 23. (NOAA)
Figure 4. Hours below 24 oF for April 10 at 7:00 am (CST) (http://mesonet.k-state.edu/)
Cold air temperatures
Air temperatures have fallen below freezing across most of the state. More importantly, parts of North Central and Northeastern KS had several hours with temperatures below 24 oF (Figure 4). These cold temperatures will translate to cooler soil temperatures. This is particularly true for areas with drier soil surfaces, less residue and if the cold air temperatures persist.
Optimal soil temperature for emergence
Every summer row crop has an optimal soil temperature for emergence. A minimum for corn is 50 oF for germination and early growth. However, uniformity and synchrony in emergence is primarily achieved when soil temperatures are above 55 oF. Uneven soil temperatures around the seed zone can produce non-uniform crop germination and emergence. Lack of uniformity in emergence can greatly impact corn potential yields. This is particularly true for corn, since it is the earliest summer row crop planted. When soil temperatures remain at or below 50 oF after planting, the damage to germinating seed can be particularly severe.
The impacts of a hard freeze on corn are discussed in detail in a previous eUpdate article and can be viewed at the following link: https://bit.ly/3bQ41k4
More information about the planting status of summer row crops will be provided in upcoming issues of the Agronomy eUpdate. Stay tuned!
Ignacio Ciampitti, Crop Production and Cropping Systems Specialist
Mary Knapp, Weather Data Library
Christopher “Chip” Redmond, Kansas Mesonet Network Manager