Cold Soil – Early Planting & Corn Emergence​​​​​

We’ve all been there: It’s the end of April, the day lengths are increasing and the calendar says it’s time to plant corn; however, the soil temperature readings continue to hover around 40˚ F. The question arises from across the area, “Do I plant or leave the seed in the bag until conditions improve?” When it comes to management decisions that can positively or negatively impact a crop’s potential, planting ranks as one of the, if not the, most important factors we can influence. For some, the need to cover acres is a real concern, and in many cases, producers decide to push the envelope and proceed with planting in less-than-ideal conditions. When this occurs, there are some management decisions a producer can make to help maximize the crop’s germination and emergence potential while minimizing the negative impact that may occur from adverse environmental conditions. 

What are current soil conditions like?

After planting, a corn seed requires adequate soil moisture and a soil temperature around 50˚ F to germinate. The length of time that it takes for the seed to germinate can range anywhere from 90 to 150 growing degree days (GDD). Moisture and temperature can vary greatly based on field characteristics such as amount of cover, tillage practice, slope, soil texture and current moisture status (Figure 1). Wet soils or fields with considerable amounts of cover or residue, such as in a no-till situation, tend to have lower soil temperatures when compared to fields that are strip-tilled or conventionally worked. 

Figure 1.

To help identify potential issues with a field, it is always a good idea to monitor soil moisture conditions and temperatures leading up to and during the start of planting. While soil temperature plays a big role in stand establishment, planting in too wet of soil conditions can have equally adverse effects. Planting in overly saturated soils can lead to issues ranging from compaction, side-wall smearing, reduced seedling root growth, and improper seed trench closing and reopening when soil conditions dry out which ultimately can lead to reduced or uneven stands.

The first 48 hours after planting are critical in determining how stand establishment may progress because of the rapid uptake of water by the seed during this time. Soils that are saturated and below 50˚ F can lead to issues with imbibition and cold chilling during germination. These events can occur when sub 50˚ F soil water is absorbed into a dry seed to begin the germination process during this time frame. Seed imbibition occurs when cold water is imbibed by a relatively warm seed that results in the seed swelling and usually without radical emergence. Seedling chilling occurs when the cold soil temperatures kill cells on one side of the mesocotyl while cells on the other side continue to grow rapidly, causing deformed seedlings (Figures 2 and 3). While many of today’s corn products are bred to endure these more adverse conditions, in certain situations this chilling affect can be overpowering and ultimately affect overall seedling growth and stand establishment. 

Figure 2.
Figure 3. Varying impact of cold water uptake in corn seedling from the same field.

How can you manage through these conditions?

While it’s not always a clear-cut answer as to when is the right time to begin or continue planting, there are several indicators you can use to help in your decision-making process. The first factor would be monitoring soil moisture and field conditions. Planting when conditions are right can have the biggest impact on your stand establishment and can be the most critical decision you make. By waiting an extra day or two in some instances for conditions to improve can sometimes mean the difference between establishing a stand or having to replant.

The second factor to consider is looking at the weather forecast and determining the temperature trends for the next three to five days. If soil temps are conducive for planting and temperatures look to be constant or climbing above 50˚ F, that would favor moving ahead with planting. If the adverse is true and soil temperatures are forecasted to decline below 50˚ F over several days, holding off on planting may be warranted. The same can be true for rainfall events. Planting ahead of a high probability of heavy pounding or soaking rain could create an adverse environment for seedling development. Not only could seed be washed out or buried, but heavy rainfall could also lead to soil crusting, which could impede stand establishment. Additionally, a combination of cool and wet conditions for a prolonged period following planting could lead to additional stress caused by potential increased disease and insect pressure due to the environmental conditions.

Maintaining proper seeding depth can also help buffer some of the negative impacts of both temperature and moisture fluctuations. Planting into adequate moisture and at a consistent depth of at least 2 inches can help encourage uniform emergence. By consistently placing seed at this level, the soil can help buffer against air temperature swings early in the season. As the season progresses, seeding depth may need to be adjusted as field conditions change or as soil moistures vary.

Lastly, utilizing effective seed treatments can be a valuable tool. Effective fungicide and insecticide seed treatments can help with stand establishment and protect early corn development from early season pest and disease pressures. This can be a key management tool, especially for those early planted acres when more time will be needed for crop emergence and stand establishment. 

Summary

Because stand establishment is so critical to the success of the growing season, determining when to start planting corn continues to be a challenge for producers. Taking time to review some of the management steps that can be used to help in this decision can help achieve success. By monitoring field planting conditions, soil temperatures, soil moisture, product selection, planting depth and weather forecast, a planting determination can be made. While the hardest choice to make is to hold off and wait for planting conditions to improve, sometimes this call may be the most profitable decision you can make in the end. ​​​​​​​

Brian Buller

Agronomist

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