Crop Comments: If corn could talk
There are four basic categories for inputs required for successful crop production: solar radiation, moisture, warmth (soil and air) and soil nutrients. We can argue that they’re all equally important, because if any one is seriously limiting, crop production rapidly suffers.
The input category threatened most by wildfire smoke is solar radiation, the most common unit of measure of which is the Langley (Ly). Ly is defined as “a unit of heat transmission, especially used to express the rate of solar radiation.” Named after the English scientist Samuel Langley, Ly is defined as “a unit of solar radiation equivalent to one gram calorie per square centimeter of irradiated surface.”
Accepting that Ly doses are not directly under human control, Chinese plant scientists want to build a less shade-sensitive corn. Researching that goal further, I located a paper titled “Quantitative Relationship Between Solar Radiation and Grain-Filling Parameters of Maize.” Written by Yushan Yang, Ph.D., and associates, it was published in Frontiers in Plant Science in June 2022. That research was conducted at the College of Agronomy, Shihezi University, Shihezi, China.
Here’s that paper’s summary: “Workers stressed the need to understand the factors driving changes in corn grain filling as being essential for effective prioritization of increasing maize yield.” Quoting these scientists: “Grain filling is a significant stage in maize yield formation. Solar radiation is the energy source for grain filling, which is the ultimate driving factor for final grain weight and grain-filling capacity that determines maize yield. Here we confirmed the quantitative relationships between grain filling parameters and photosynthetically active radiation (PAR), by conducting experiments using different shading and plant density conditions and cultivars in 2019 and 2020 in Xinjiang, China.”
These workers also wrote that relative changes in PAR were significantly and positively correlated with relative changes in yield and grain filling rate. I’ll side-step the more technical explanations from these scientists and jump to their conclusion: “We believe that with increased likelihood of factors continuing to decrease PAR, plant geneticists should place more emphasis on developing corn strains that are less susceptible to erosion of effective solar radiation.”
In the June 24, 2025 edition of the Michigan Farm News, Dennis Rudat wrote an article titled “What effect does wildfire smoke have on Midwest crops?” He wrote that over 38 million acres of Canadian forests burned in 2023, more than double any previous year, making it the worst wildfire season in Canada’s history. He added that in the U.S. wildfires over the past 40 years have seen a four-fold increase from around two million acres annually to over eight million. Thus, as smoky days become more common in agricultural regions, corn and soybean producers increasingly ask how wildfire smoke affects their crop’s productivity.
Rudat forwarded that question Mark Jeschke, Ph.D., agronomist at University of Madison-Wisconsin, who explained that relationship between wildfire smoke and crop growth is complex, both with positive and negative effects on photosynthesis. Jeschke further explained that three factors determine how smoke influences photosynthesis:
First was reduced sunlight intensity. Like hazy cloud cover, smoke reflects incoming sunlight, reducing the amount of light available to plants. Because plants need sunlight to carry out photosynthesis, any reduction in light is potentially detrimental to crop productivity.
The second factor was increased sunlight diffusion. In this scenario, wildfire smoke can significantly increase the diffuse fraction of photosynthetically active radiation. Oddly enough, this can benefit plants by increasing light use efficiency, as well as the availability of light to lower canopy leaves.
His third factor listed was ground-level ozone (O3), an air pollutant, harmful to human health and plant growth. Elevated O3 often greatly reduces crop yields. Dicot species, like soybeans, are believed to be more susceptible to yield reduction from O3 than most monocot species, like corn.
Crops depend on sunlight to photosynthesize and achieve high yields, and a reduction in solar radiation, especially during the critical grain-filling period, can be harmful. Quoting Jeschke: “The risk of yield loss and reduced stalk health from wildfire smoke is likely greater when smoke imposes an additional stress on a crop that is already experiencing the effect of other stresses, like disease or drought stress. Reductions in yield can be dramatic. Studies that have included shade treatments, that reduce light by 50% or more during grain fill, have seen corn yield drop by more than half” (similar to what the Chinese agronomists observed).
Jeschke further explained that in addition to direct effects on corn yield, reduced solar radiation can also impact stalk quality and standability. Upon successful pollination, ear development places a great demand on the plant for carbohydrates. When demands of the developing kernels exceed the carbohydrate supply produced by leaves, stalk and root storage reserves are utilized to take up that slack. Environmental stresses which decrease the amount of photosynthesized material produced by the plant can force plants to extract even greater percentages of stalk carbohydrates.
As “carbs” stored in the roots and stalk are mobilized to the ear, these structures begin to decline and soon lose their resistance to soil-borne pathogens. Instances of severe stalk rot and lodging are frequently observed in association with prolonged periods of low solar radiation during grain fill.
The increase in fire risk in North America has been driven by two major factors: Increased fuel load in forested areas, resulting from decades of fire management practices focused on fire suppression, and increased fuel dryness, due to a hotter and drier climate.
Jeschke concluded, “Given what is known about the factors that have led to increased wildfire activity, it’s a virtual certainty that wildfire smoke in the atmosphere will continue to increase in frequency and concentration for the foreseeable future, making it important to understand how crop growth and productivity might be affected.”
by Paris Reidhead
