We continue to read, see and hear stories of how this year's U.S. corn crop has not met expectations at harvest. Many of the accounts focus on crop problems related to how cloudy and humid conditions during midsummer favored pests and diseases. Their presence and activity in the fields were notable impediments to corn yield.

However, this past summer's weather pattern also simply deprived corn plants in some top-producing locations of the solar energy required to fully perform. "I have heard more about the lack of sun than almost anything else when it comes to this past growing season's weather," said University of Nebraska-Lincoln Extension Ag Meteorologist Eric Hunt. Hunt's comments relate to harvest yields that are well below typical numbers.

Nebraska's York County offers an example of significantly lower yields in 2025. Fields which typically yield over 240 bushels per acre (bpa) produced a full 25% less -- just 180 bpa. Nothing was different in terms of soil and seed quality, fertilization and irrigation, but the combine monitors still showed a big decline from normal. And, possibly not coincidentally, the amount of solar radiation in cornfields during July was far less than the usual amount. Measurements catalogued by the Iowa Environmental Mesonet show from July 4 through July 24, 2025 -- a key grain-filling time -- York County had 12 days, almost two full weeks, with solar radiation that was below to much below average. "We had a significant deficit of solar radiation across this region," Hunt said on the Nov. 7 edition of the Nebraska Public Television "Market Journal" program.

Research done by the seed industry has concluded that a lack of sun during corn pollination and grain fill can indeed reduce yields. Summary comments from a Golden Harvest Seeds 2020 article, titled "Impact of Solar Radiation and Light Availability on Corn Yield" note: "Low solar radiation has the biggest effect on yield during silking and grain-fill periods. Experiments that intentionally shaded corn to approximately 50% solar radiation reduced yield by 12-20% when shaded during silking and by 19-21% when shaded during grain fill ... Shading during silking results in ear tip-back or fewer kernels per row whereas shading during grain fill results in decreased kernel weight from shallower kernels."

Also, solar radiation research done by Pioneer Seeds in 2015 found the beginning stages of new corn kernels -- the silking stage (R1) and the very early kernel development stage (R2 or "blister") -- are very sensitive to environmental conditions. And in York County Nebraska, those very-sensitive corn kernel stages line up exactly with the lower solar radiation in July 2025.

This lack of sunlight was not universal across the U.S. But where it occurred, it had a telling impact in the grain tank with yield reduction and added pressure on the business ledger as we conclude the 2025 row-crop season.

Bryce Anderson can be reached at bryce.anderson@dtn.com

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