Soybean Yields In Kentucky- Past, Present And Future

DR. DENNIS B. EGLI

LEXINGTON, KENTUCKY

Kentucky’s soybean crop got off to a good start in 2025. Plentiful rains produced an estimated yield on August 1 of 52 bushels per acre (bu/a) according to the National Agricultural Statistics Service (NASS).  A yield of 52 b/a is not a record (the Kentucky record is 56 bu/a in 2021), but it was only slightly below the trend line (Fig. 1). Not a bad year, but then the roof fell in. The September 1 estimate was only 40 bu/a – a drop of 12 bushels (23%).

What happened in August? Very simply, it stopped raining. August was the driest month on record in Kentucky, according to Matt Dixon, Senior Meteorologist in the UK Ag Weather Center (Dixon, 2025). The state averaged 1.29 inches in August (2.5 inches below normal) after the first part of the year (January through July) was the wettest on record. 

This dramatic yield reduction simply reinforces what we already know – crops can’t grow without water, actually a lot of water. A well-watered soybean crop can use 0.25 inches or more per day in July and August. That means the crop needs an inch of rain every four days. Getting that much rain regularly is nearly impossible, so stored soil water has to make up the difference.

Erratic rainfall and the enormous water demand by the crop explains why the capacity of the soil to store water is so important. The soil water reservoir serves as a buffer between intermittent rainfall and the constant daily water use by the crop. Soybean yields are usually higher, especially in years with limited rainfall, on deep soils that store a lot of water. Soil water storage explains why soybean yields in Iowa and Illinois are usually higher than in Kentucky. They are blessed with deep soils that store a lot of water, while we must make do with a lot of shallow soils.

Despite this limitation, Kentucky soybean yields have increased dramatically in the last 45 years (Fig. 1). There were good years and not so good years, but the trend was always upward. The trend-line yield in 1980 was only 25.5 bu/a; it more than doubled to 53.1 bu/a in 2024 (Fig. 1). The increase is even more dramatic if we go back to the beginning. In 1924, when soybean yields in Kentucky were first reported by NASS, the yield was only 9.5 bu/a - yields increased roughly 5 fold in about 100 years – an extraordinary record of growth.

Development of new, improved varieties and better management practices (including better weed control) accounts for the bulk of the growth. Some scientists argue that improved environmental conditions (e.g., clearer skies that allowed more sunshine to reach the surface) accounted for some of the growth.   

Scientists argue about who made the biggest contribution – plant breeders or the crop management folks, but it is nearly impossible to isolate the causes of yield growth because they are interdependent. Improved varieties cannot express their high yield potential without better management, and you can’t manage an old variety to produce today’s yields. Trying to isolate the factors responsible for higher yields is a futile task.

The harvested acres of soybean in Kentucky increased from about 1.2 million acres in 2000 to 2.04 million in 2024 (NASS). Increasing acres are often thought to be a drag on yield increases. The assumption is that the best land goes into production first, so increasing acres are on less productive land, slowing the yield increase. There is no evidence in Fig. 1 that the increase in acres reduced the yield increase.  

Will this increase continue? A pessimist could argue that yields have reached a plateau (no yield increase since 2020, Fig. 1). An optimist could point out that these apparent plateaus have occurred before (1993 – 1997, 2003 – 2006), but the yield increase eventually continued. Future genetic improvement will probably benefit from the wonders of biotechnology, but, on the negative side, climate change may create a more hostile environment that limits yield growth. It’s impossible to predict which scenario will rule in the future, but, don’t forget “The pessimist complains about the wind, the optimist expects it to change, the realist adjusts the sails” (William A. Ward, college administrator and writer, 1921-1994).

References

National Agricultural Statistics Service (NASS), USDA. 2025. Quickstats.nass.usda.gov.

Dixon, M. 2025. Fourth Straight Fall, Same Story: Drought Conditions Return to Kentucky. Kentucky Field Crops News, Vol 1, Issue 9. University of Kentucky, September 12, 2025.  ∆

DR. DENNIS B. EGLI

LEXINGTON, KENTUCKY