Soil Temperatures and Planting Considerations
Spring has arrived with warmer-than-normal daytime temperatures and adequate rainfall across most of the state. With warmer ambient temperatures it can be hard to resist the urge to get the planter up and running, but there are other considerations that need to be made before seed touches soil.
Soil temperature is an important aspect of getting the growing season off to a good start. Corn should not be planted until soil temperatures are 50 degrees Fahrenheit or warmer. The reason for this has to do with the relationship between soil temperature and soil moisture. Corn seeds will absorb 30% of their weight in water and this will spur the development of roots and shoots. In cooler soil temperatures the corn seed will still absorb water, but will not germinate, or will germinate poorly. This could lead to poor emergence and uneven stands.
Recently, we visited fields around St. Johns and DeWitt, Michigan to see what soil temperatures were reading under different field management. The results of 11 soil temperature readings at a 4-inch depth are in the table below.
Soil temperatures around St. John’s Michigan, April 6, 2021
|
Soil Temperature in F |
Field Details |
|
58.1 |
2020 wheat field, tilled with manure knife, moderate residue |
|
60.8 |
2021 wheat field |
|
59.7 |
2021 wheat field |
|
61.0 |
2020 soybean field, intensive tillage, little residue |
|
60.1 |
2020 soybean field, not tilled, moderate residue |
|
57.2 |
Cover crop with high residue and stand count |
|
69.0 |
2020 corn field, chisel plowed, high moisture content, little residue |
|
55.9 |
2020 corn field, winterkilled oat cover crop, high residue |
|
59.4 |
2020 corn field, not tilled, moderate residue |
|
59.2 |
2020 soybean field, not tilled, moderate residue |
|
59.7 |
2020 corn field, tilled, little residue |
The average soil temperature across all fields was 60.0 degrees Fahrenheit.
Different management actions can lead to differences in soil temperature at this time of the year that can also carry through the growing season. The average soil temperature of fields from our visits that had been tilled (any kind of tillage) was higher than fields that had not yet been tilled: 61.9 degrees compared to 58.6 degrees. In the example below, we found a soybean field that had been partially tilled at the time of our visit. The portion of the field that had been tilled was 1 degree warmer than the untilled, higher residue side of the field.
Residue cover on the soil surface can also impact soil temperature. Fields with moderate-high residue cover may take longer to warm up in the spring than fields with little soil cover. We found this to be true in fields with moderate-high residue cover having a lower soil temperature (58.4 degrees) than our regional average (60.0 degrees). The benefit to this soil coverage comes later in the growing season when residue can help to preserve soil moisture when water becomes a limiting factor in the summer months.
Like residue cover on the soil surface, the presence of a cover crop can also impact soil temperatures in the spring by delaying warm-up of the soil. Two fields with a cover crop – one living and one winterkilled – showed the lowest soil temperatures of all fields visited. The picture below is the field we visited with the living cover crop (57.2 degrees). Despite the potential for lower soil temperatures in Spring, having a living cover crop in the field, even for a short period, will benefit the microbial community, help with nutrient cycling and will increase overall soil health.
