It’s hard not to be itching to get in the field and start planting, especially since we are past the April 11th crop insurance date for planting. However, the optimum planting date is dictated by soil conditions (moisture and temperature), the weather forecast, and the calendar date – not just one of these.
While the rule of thumb to start planting is that soil temperatures should be 50°F at the 4-inch depth and warming before we start planting, we also need to consider the conditions after planting. It typically takes 100 to 120 Growing Degree Days (GDDs) to accumulate from planting for corn to emerge (Nielsen, 2020) and 90 to 130 GDDs to accumulate from planting for soybeans to emerge (Conley and Gaska 2010; Casteel, 2010).
When we calculate GDDs early in the season, we should look at the soil temperatures rather than the air temperatures. The warmer the soils, the more GDDs we accumulate, and the faster emergence occurs. Current average soil temperatures around the state are right around 50°F.
How long until crops emerge:
- Soil temps in the 40s = ~3 weeks to emerge
- Soil temps in the 50s = ~2 weeks to emerge
- Soil temps in the 60s = ~1 week to emerge
The longer emergence takes, the risk for stand loss due to early season insect pests or seedling diseases increases. Additionally, crops in cold soils are more prone to cold injury while imbibing water and during early growth. Extension educators at the University of Nebraska-Lincoln ran an interesting test last week to demonstrate cold temperature effects on soybean during the imbibitional process that you can see here.
The short-term forecasts are showing the cooler conditions persisting for the next several days, with especially cold temperatures early this week. Continue to be patient and wait for soil conditions to become ideal for planting. We are still within the optimum planting window for corn (April 11 to May 18) and soybeans (April 11 to May 20). The quicker germination and emergence occur, the more uniform and vigorous stands will be.
Nielsen, R.L., 2020. The Emergence Process in Corn. Corny News Network. Purdue University.
Casteel, S. 2010. Soybean Physiology: How Well Do You Know Soybeans? Purdue University.
Conley, S.P. and J. Gaska. 2010. Predicting When Soybeans Will Emerge. Cool Bean. University of Wisconsin.