By University of Tennessee Extension

Soybeans and corn are Tennessee’s top two row crops by planted acreage, contributing over $1.2 billion and $1.7 billion respectively to the state’s economy each year. University of Tennessee Extension Corn and Soybean Specialist Jake McNeal with the University of Tennessee Institute of Agriculture offers insight into capturing additional yield potential in soybeans with an earlier-than-normal planting window.

“We love soybeans in Tennessee,” says McNeal. “Our state average yield tracks very closely with the national average of right at 50 bushels per acre. It is an incredibly versatile crop with a very wide acceptable planting window. Much of my soybean research focuses on exploring the optimal maturities and planting populations that maximize yield for producers across this broad range of time”.

Building on research from neighboring states, McNeal’s work has shown that planting soybeans earlier has a yield benefit as compared to when planted later. “Early is a relative term and is only loosely tied to a calendar date. There is a lot of geographical and agricultural diversity in Tennessee, and this is reflected in planting dates for both corn and soybeans.”

In 2023, his research demonstrated a three bushel per week yield penalty for soybeans planted from March 20 to April 30. From May 1 to May 30, the yield penalty increased to approximately 5.5 bushels per week.

Not every acre

However, McNeal cautions against planting every acre early. “There is definitely a cliff behind us and we don’t want to back up too much and fall off.” He says that the earlier soybeans are planted in the spring, the earlier they will canopy. When this happens, airflow within the crop decreases. “Planting early never causes disease. But when a dense canopy coincides with a high moisture environment and disease-causing pathogens are present, this can lead to higher levels of disease incidence.”

For most years, McNeal says the benefits of an early planting date outweigh these concerns. “Neighboring states have had success planting soybeans during an early planting window for some time. However, their production practices are different than most Tennessee producers in several substantial ways. A large portion of their acreage is conventionally tilled and bedded. These soils dry out and warm up faster than ours in Tennessee, which are almost exclusively no-till”.

Currently utilized by more than 90% of row crop producers in Tennessee, no-till production practices often result in soils that remain cooler and wetter later into the spring than soils that are conventionally tilled. Many producers in Tennessee wait an additional two to three weeks to plant compared to neighboring states. “A practical management plan is to start planting soybeans in the last few weeks prior to corn. When it’s time to start planting corn, swap. At this point, I can’t recommend an early planting date for all of our soybeans. However, we have enough data for me to encourage producers to shift their mentality in that direction.”

For corn, McNeal says there is a yield penalty if planted too early, as it is much more sensitive to at-planting soil conditions compared to soybeans. However, if you delay planting too far into May, you often see another yield penalty. “There are times that a late-planting corn window is unavoidable as we are always at the mercy of the weather.”

Corn

High-yielding corn requires uniform germination and emergence, which is highly influenced by at-planting soil conditions. “With soybeans, you can get away with delayed or uneven emergence without major yield penalties. In this sense, soybeans are a little more forgiving than corn.”

McNeal says he will continue his research in 2024. “We will be looking not only at planting dates, but also at seeding rates across these planting dates. Our goal is to aid producers in maximizing yield regardless of what their planting dates may be.”

For more information on planting dates and agricultural practices in your area, please contact your local county Extension office.