What’s Driven Corn and Soybean Yields Higher Over Time?

The upward trend in U.S. corn and soybean yields is well known, but what specific plant-level factors have pushed higher yields over time?

The USDA reports state-level data for corn that allows the effects of plant population, corn ears per plant, and ear weights to be considered. Since the late 1980s, all three factors have trended higher, implying they’ve all been important. But which has been most consequential?

In Iowa, corn yields have increased by around 96 bushels per acre since the late 1980s. Of those bushels gained, 61% can be attributed to higher plant populations. One way to think of this is that planting at 1986-1990 populations would remove a lot of yield potential.

Ear weights contributed 34% of yield gains. It’s worth mentioning that ear weights are the biggest source of variation on an annual basis. This means that yield surprises are likely to show up in ear weights.

For soybeans, the available metrics are pods per 18 square feet and pod weight. Over time, 71% of soybean yield gains have come from higher pod counts. Unfortunately, it is unclear whether those pods are coming from planters per acre or pods per plant.

Wrapping it up

At the farm level, these data are a reminder that producers can be more specific and precise when managing their own crops. For example, if 2024 corn yields are disappointing, is the source population, ear weights, or ear count? From there, specific management changes could be considered and addressed.