Fundamentally Speaking

Corn Ear Population and Yield Growth

Joel Karlin
By  Joel Karlin , DTN Contributing Analyst
Chart by Joel Karlin, DTN Contributing Analyst

In an earlier blog piece on corn ear weights, we noted an interesting side note is though the U.S. has seen back-to-back years of record corn yields, both years are actually below the 25-year trend as corn yields appear to be plateauing similar to what we have seen with soybean yields where a new national yield record has not been set since 2016.

It could be that the long-term growth in corn plant and ear populations is slowing as from 2004 to 2014 the USDA ten state objective corn ear populations increased by an annual average of 236 per season but from 2014 to 2024 that has slowed to just a yearly increase of 24 ears per acre.

In this chart we break it down further by showing the slope of the corn ear count populations on the left-hand axis and the slope of the corn yield changes on the right-hand axis for each of the USDA's ten corn objective states for three time periods (1995-2025 and then broken down into two 15-year periods, 1995-2009 and then 2010-2024).

The only exception is in Kansas, Missouri and South Dakota where the USDA's corn ear count data began in 2004, so the blue column is 2004-2024, orange column is 2004-2014 and grey column is 2014-2024.

Illinois had the highest change in ear count data as in the 30-year period from 1995 to 2024, the average annual increase in that state's corn ear population rose by 300, but from 1995-2009 it rose by an average of 414 per year, but has slowed over the past 15 years to a rate of 277 per year from 2009 to 2024, still the highest for both periods.

Note that IL is not alone as all the other nine states saw corn ear count populations increase at a much slower rate from 2009 to 2024 as opposed to the earlier 15-year period as many have seen ear count population growth less than half of what was seen in the earlier 15-year timeframe.

The states of KS, MO and SD have actually seen ear populations trend lower over the past ten years as opposed to what was seen in the 2004-2014 period, especially in KS.

This helps explain why over the past 30 years, Kansas has seen its corn yield trend lower by an average of 0.29 bushels per acre (bpa) per year and over the past 15 years has seen the slowest yield increase of just 0.61 bpa/year.

On the other hand, IL with the highest corn ear populations has seen the highest average annual yield increase of 2.81 bpa over the past 30 years with the 3.86 bpa/year annual increase from 1995-2009 increasing to 4.83 bpa/yr from 2010 to this past season.

Looking at states such as IA, MN, and NE, the fact that the rate of corn yield increases per year has slowed in the more recent 15-year period seems related to their reduced pace of increasing corn ear populations per acre, along with perhaps more adverse growing conditions in those states that also suppressed the other part of the yield equation which is the weight of each individual corn ear.

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