By Jim Specht, Agronomist; Jenny Rees, Extension Educator, Patricio Grassini, Cropping Systems Specialist; Keith Glewen, Extension Educator
Planting as early as 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:
- Losing crop insurance benefits by planting before "earliest" planting dates
- Plant damage due to cold soil temperature the first 48 hours after planting
- 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 2-day 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, University of Nebraska agronomist 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 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 first trifoliolates exposed to the air. Staggering planting dates can help with staggered emergence dates, thus reducing your risk if a late spring freeze occurs.
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 vs. 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.)