Three Key Considerations for Planting Corn and Soybeans

Three Key Considerations for Planting Corn and Soybeans April 15, 2016

Planting as early as is reasonably possible allows your crop to collect solar radiation sooner. This also carries risks that should be weighed against the benefit. These risks include, but are not limited to:

Photo of thermometer in the soil
Check soil temperature the same morning you plan to plant. (Photo by Nathan Mueller)

Key Tip

Check the soil temperature at the field(s) you want to plant that day (using a cheap meat thermometer or two), and then assess the soil temperature forecast for that same evening and the next day and evening. If the morning soil temp is currently at or above 50°F and is not likely to fall lower than 50°F in the next 48 hours, consider planting.

  • losing crop insurance benefits by planting before "earliest" planting dates, 
  • plant damage due to cold soil temperature the first 48 hours after planting,
  • frost, and
  • related costs and labor of replanting.
1. Crop Insurance

Crop insurance is an important factor to consider when it comes to the earliest date you can plant your crop.  We are currently past the April 10 and April 15 Risk Management Agency (RMA) earliest dates for planting corn in Nebraska. The earliest date for soybeans is April 25.

2. Soil Temperature the First 48 Hours after Planting

Once planted, corn seeds need a two-day (48 hour) window when the soil temperature at planting depth does not drop much below 50°F. Imbibitional (fast) water uptake occurs within the first 48 hours after a seed is planted.  When the soil temperature drops much lower than 50°F within that time frame, there is potential for chilling injury which can affect seed germination. After that 48-hour time frame, reductions in soil temperature below 50°F are less likely to affect germination as later water uptake occurs via osmosis and is slower. Temperature drops after the first 48 hours can make for slower emergence; however, they shouldn’t result in death of the germinated seed and seedlings. Jim Specht, UNL emeritus professor of agronomy, tracked these soil temperature differences and the effect on soybean germination both within the first critical 48 hours and afterward. His findings are in this CropWatch article.)

3. Late Spring Freeze

With early planting, the risk of a late spring freeze will rise as will the probability of a higher yield. A key point to remember is that spring freeze risk only applies to emerged seedlings. Air temperatures of 28°F or less may result in damaged tissue and even death if the growing point is affected, potentially resulting in a replant decision. It is the number of hours below freezing (32°F) plus the type of exposed tissue that determines the degree of crop freezing injury. For example, just-emerged soybean seedlings in the cotyledon stage are less likely to be injured than seedlings that have unifoliolates or 1st trifoliolates exposed to the air. Staggering planting dates can help with staggered emergence dates, thus reducing your risk if a late spring freeze occurs.

Plant tissues typically do not freeze when the air temperature around them is 32°F.

The reason is because solutes are present in the membrane-bound cytoplasm (and also just outside of cell membranes) and they act like a very modest anti-freeze. Thus, plant tissue usually does not freeze until the tissue temperature reaches 30°F to 28°F (i.e., -1 to -2C). When you examine the last spring freeze risk probability table, use the 28°F not the 32°F freeze risk.

Source: Pearce, R.S. 2001. Plant Freezing and Damage. Annals of Botany 87:417-424.

Rain presents another risk consideration such as in spring 2015 when rains prevented timely planting in some areas and in some cases, made it impossible.

Thus you must weigh the risks of a late spring freeze versus not being able to plant in a timely fashion due to weather constraints. Probabilities for a late spring freeze (28°F) for many areas of Nebraska are available in this National Weather Service table.  (For more information see Risk of Freeze Damage in Early Planted Corn in this week's CropWatch.

Conclusion

As you begin planting:

  • keep in mind crop insurance dates,
  • know your soil temperature and, before you plant, check the forecast for the next 48 hours, and
  • consider your potential for late spring frost. 

Here’s wishing you a successful planting season!