Warm weather is sneaking up on farmers across the country, which means one thing: it’s go time. But don’t forget to assess soil temperatures before planting.

Soil temperature plays a pivotal role in the early stages of plant growth, particularly in seed germination and seedling development prior to emergence. Inadequate soil temperature, especially if it is too low, can hinder the germination process and may cause permanent stunting of growth, even if germination does occur.

To ensure optimal seed germination and growth, we recommend that the soil temperature reaches at least 50°F for corn and soybeans. However, a few factors may permit planting in temperatures below 50°F.

Growing degree units (GDUs):

GDUs, also known as growing degree units, are used to track the accumulation of heat during the growing season. To calculate GDUs, the daily maximum air temperature plus the daily minimum temperature is added together and divided by two, to get the daily average. The base temperature (50°F) is then subtracted, giving you the final GDU number for the day. Begin computing the daily GDU values from the day of planting and continue tracking them throughout the entire growing season. Sum up the daily GDU values to determine the number of days required to achieve a specific growth stage or developmental milestone. 

As an illustration, supposing the highest temperature of the day reaches 80°F and the lowest temperature is 60°F, the daily average temperature is computed by subtracting the low temperature from the high temperature and dividing the result by two. By subsequently subtracting the standard base temperature of 50°F from this value, the resulting sum is equivalent to the total number of GDUs accrued on that particular day, which in this instance is 20. This methodology enables accurate tracking of heat accumulation over time and provides a useful tool for estimating crop development and growth.

For both corn and soybeans, it takes approximately 100-120 and 130 GDUs, respectively, to emerge from the soil. In 50-55°F soil, it can take up to three weeks for seeds to emerge. Warmer temperatures (around 60°F) will allow for quicker emergence (about 12 days). So if planting into cooler soil, remember to evaluate the impacts of seed being underground for longer periods. These impacts could include increased damage from below-ground pests and increased risk for disease infection. 

Weather forecast:

The short- and long-term forecasts are critical to appropriately timing planting. If a warm front is approaching, planting in cooler soil temperatures can work out. In this scenario, soil temperatures will warm faster, which aids in seed germination and growth. But don’t let a few sunny, warm days sway you. Be sure to also consider the forecast for after planting and make sure temperatures are trending upwards. Sustained warm weather after planting can help ward off disease and imbibitional chilling. Always double-check local weather forecasts in the Advantage Acre app and check regional spring weather trends. 

Imbibitional Chilling:

If cooler or wet conditions are on their way in, attempt to stray away from planting, as it can cause stress on newly planted seeds. Planting into cool soils that stay cool and moist for a long time can cause imbibitional chilling, which occurs when the seed imbibes cold water in the first 24 to 48 hours after planting. This can lead to reduced stands and seedling vigor. Regardless of when (or for how long) imbibitional chilling occurs, there is nothing that can be done to change the outcome of seedling damage. If an imbibitional chilling injury is suspected, we encourage field scouting over the week following emergence to evaluate the extent of damage and assess the crop’s stand. 

Seed protection:

If seed remains in the soil for a prolonged duration due to early planting in conjunction with cold, moist weather conditions, it is advisable to invest in seed protection to prevent damage from pests and diseases. Work with an AgriGold agronomist to identify the most appropriate seed treatment that compliments seed selection and offers comprehensive protection during the entire growing season. 

Soybean plants that are planted early are prone to being attacked by diseases like Phytopthora and Pythium. These diseases can cause the decay of seeds or seedlings, ultimately impacting the crop’s stand. To fortify your crop against these soilborne diseases, consider selecting a seed treatment like AgriShield® that provides enhanced protection. 

For safeguarding corn crops from early-season insects and diseases such as Pythium, Fusarium, black cutworms, seedcorn maggots, and more, during the initial growth stage, opt for a seed treatment with enhanced protection of early-season stressors. Examples of such treatments include AgriShield® or Acceleron®.

The bottom line

• Closely monitoring soil temperature is crucial for planting corn and soybeans successfully. 
• You can make well-informed planting decisions that maximize yields and potential profits by considering weather forecasts, growing degree units, and appropriate seed protection. 
• Check soil temperatures for at least three days to help get an accurate temperature average and avoid risks associated with cold and wet soils, such as seed rot and seedling diseases. 

Don’t hesitate to contact your local AgriGold agronomist for personalized advice on soil temperatures, planting dates, and other factors tailored to your farm’s unique needs.