Planting date is one of the most critical factors to decide for row crops. Rather than just calendar dates, farmers should consider basing this decision based on soil temperature and moisture.
After a cooling trend during the second week of March, air temperatures across Kansas seem to be back to normal again but forecast indicates we may fall below normal in the coming days.
For the 7-day period between March 9-15, average soil temperatures at 2 inches across KS districts ranged from 36oF to 47oF (Figure 1). You can monitor soil temperatures across the state by using the Kansas Mesonet’s soil temperature tracking tool at https://mesonet.k-state.edu/agriculture/soiltemp/.
Figure 1. Average soil temperatures at 2-inch soil depth for the week of March 9 to 15, 2023. Source: Kansas Mesonet. (https://mesonet.k-state.edu/agriculture/soiltemp/)
Projections for the next 8 to 14 days call for leaning below-normal temperatures statewide (Figure 2). In parallel, the above-normal precipitation outlook may contribute maintaining cool soil temperatures (Figure 3).
It is worth to mention that topsoil temperature differences could be large depending on multiple factors. Actual changes in any given field will be affected by several factors including soil type, soil moisture, residue cover, tillage, landscape position, and others. For example, wet soils under a no-tillage system are expected to warm up at a slower pace. Dry soils will fluctuate more rapidly, matching air temperatures, particularly if skies are clear.
Figure 2. 8 to 14-day outlook temperature outlook for March 22 – 28, 2023. Source: NOAA.
Figure 3. 8 to 14-day outlook precipitation outlook for March 22 – 28, 2023. Source: NOAA.
Current soil moisture status across Kansas indicates particularly dry conditions toward the southwest portion of the state, increasing to moderate or high saturation when moving to north central, northwest, and northeast regions, respectively (Figure 4).
Figure 4. Soil moisture at 2 inches (5 cm) as of March 15, 2023. Source: Kansas Mesonet https://mesonet.k-state.edu/agriculture/soilmoist/
The largest weekly departure in precipitation occurred in the southeast corner of Kansas (Figure 5). After the wet upcoming week, projections for the last part of March call for precipitation to be a bit above-normal for most of the state (Figure 3).
Figure 5. Departure from normal precipitation for the first two weeks of March, 2023. Source: Kansas Mesonet.
Optimal soil temperature for crop emergence
Every summer row crop has an optimal soil temperature for its emergence. A minimum for corn is 50oF for germination and early growth. When soil temperatures remain at or below 50oF after planting, the damage to germinating seed can be particularly severe.
Uniformity and synchrony in emergence is critical and primarily achieved when soil temperatures are consistently above 55oF. 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. Competition between early-emerged and late-emerged plants, as well as competition to weeds may negatively impact biomass and grain production. Compensation mechanisms like tillering have limited potential compared to other crops compensation mechanisms like branching in soybeans.
Impact of a hard freeze on corn
Corn is also more likely than other summer crops to be affected by a hard freeze after emergence if it is planted too early. The impact of a hard freeze on emerged corn will vary depending on how low the temperature gets, the intensity and duration of the low temperatures, field variability and residue distribution, tillage systems, soil type and moisture conditions (more severe under dry conditions), and the growth stage of the plant. Injury is most likely on very young seedlings or on plants beyond the V5-6 growth stage, when the growing point is above the soil surface.
The average day for last spring freeze (32oF) is considerably variable across the state (Figure 6). From southeast to northwest Kansas; the earliest last spring freeze date is April 1-14 and latest is May 5-12. Thus, corn planting dates before the second week of April in the southeast or the second week of May in the northwest would represent a high risk of suffering from a late spring frost damage.
Figure 6. Average last spring freeze (32 degrees F) for Kansas. Source: Kansas Mesonet.
More information about the planting status of summer row crops will be provided in upcoming issues of the Agronomy eUpdate. Stay tuned!
Ignacio Ciampitti, Farming Systems
Adrian Correndo, Post-doctoral Fellow
Matthew Sittel, State Climatologist
Christopher “Chip” Redmond, Kansas Mesonet Network Manager