What Impact Does Wildfire Smoke Have on Corn and Soybean Crops?

July 21, 2026

Smoke from Canadian wildfires has drifted over large areas of the United States multiple times in recent years. In 2023, solar radiation was reduced by 32% in Indiana in late June due to wildfires in Canada during that time.1 Figure 1 shows the areas of the United States with air quality concerns during another wildfire event in July, 2026. Many growers and agronomist may be asking themselves: What impact does this wildfire smoke have on growing crops?

Key Takeaways

  • Heavy wildfire smoke can reduce sunlight reaching crop canopies.
  • Diffuse light may benefit lower leaves but rarely offsets major sunlight reductions.
  • Corn is generally more sensitive than soybean to reduced solar radiation during reproductive and grain fill growth stages. 1,2
  • Smoke-related ozone can damage plant tissues and reduce productivity.
  • Overall yield impacts depend on smoke intensity, duration, timing, and growing conditions.
Map of Canada, United States, and Mexico which shows the location of fires and smoke on a wildfire smoke map for July 20, 2026.
Figure 1. Locations of fires and smoke in North America on July 20, 2026. Image from National Oceanic and Atmospheric Administration.

How can Smoke Impact Photosynthesis in Corn and Soybean?

Atmospheric smoke may reduce the amount of solar radiation in a way similar to cloud cover. The reduction in solar radiation may impact certain plants more than others. Many warm-season crops, such as corn and sorghum, fix carbon using the C4 photosynthesis process. When solar radiation is reduced, C4 plants can be impacted to a greater degree than plants that photosynthesize using the C3 pathway. This is because C4 plants have a higher light saturation point, which is the point when additional light intensity no longer increases photosynthetic rates. C4 plants, like corn, are the most susceptible to reductions in light during the reproductive and grain fill growth stages.1,2

Soybean and wheat, which are C3 plants, have a lower light saturation point. Due to their lower light saturation point, soybeans and other C3 plants are not impacted as much by reduced light. However, yield of C3 plants can still be impacted under prolonged reductions in radiation.7

Particles and gases in the atmosphere absorb and scatter light as it enters the atmosphere, making the light more diffuse. This is particularly true for blue light, which has a very short wavelength. Blue light and red light can increase the photosynthetic capacity of corn. Thus, atmospheric smoke may increase the scattering and diffusion of light, allowing for greater penetration deeper into the crop canopy.2 This potentially provides a boost in photosynthesis if enough total solar radiation filters through the smoke.

Canadian wildfire smoke appears like a dense fog in this picture of Pine River, Wisconsin.
Figure 2. Smoke over Pine River, Wisconsin, June 28, 2023.


Canadian wildfire smoke appears over a field of soybeans in Pine River, Wisconsin.
Figure 3. Smoke over Pine River, Wisconsin, June 28, 2023.

Why is Ozone Produced from Smoke Bad for Corn and Soybean Plants?

Wildfire smoke is a combination of various gases, particulates, organic compounds, and water vapor. The gases can include carbon monoxide, carbon dioxide, nitrogen oxide, several volatile organic compounds (VOCs), and small particulates.3 The VOCs and nitrogen oxides combine in the presence of sunlight to produce ozone. It is important to note that ground-level ozone formation depends on atmospheric conditions and may not increase uniformly during every smoke event.

Ozone formation, while beneficial in the upper atmosphere, is very damaging to plants at ground level. As ozone enters the leaf, this highly reactive form of oxygen interferes with photosynthesis and damages plant tissue on a cellular level, increasing the rate of senescence. Studies conducted by the University of Illinois found that over the last 30 years, ground-level ozone has reduced corn yield by 10% and soybean yield by 5%.4

What is the Overall Impact of Smoke on Corn and Soybean Yields?

The effects of wildfire smoke on crop productivity are complicated and have not been well researched.5 While the light diffusion caused by airborne particulates may be beneficial in increasing the photosynthetic availability of blue light, the overall decrease in solar radiation is likely to outweigh the benefit. A 2019 study found that an artificial 15% reduction in solar radiation resulted in yield reductions in some corn products.5 Wildfire smoke may also indirectly affect overall plant health. The reduction in photosynthetic capacity caused by the reduction in total solar radiation further causes the corn plant to re-mobilize carbohydrates from the stalk and roots to the developing grain, increasing the risk of poor stalk and root health.

However, a California study found that smoky conditions increased the light-use efficiency (defined in the study as the ratio of productivity to absorbed radiation), and that this value was nearly doubled for corn. Although this enhanced efficiency is dependent on the trade-off between reduction in total solar radiation and the increase in the amount of light diffused.6

On a clear sunny day, plant canopy light values (measured as photosynthetic photon flux density, PPFD) range from 1200 to 1800 µmol per m2 per s (micromole per meter squared per second). On cloudy days, PPFD is only 100 to 400 µmol per m2 per s. In an Ohio study, the authors compared PPFD of days with wildfire smoke and cloudy days to the longer-term average over the same time period.7 The daily reduction in June from smoke and cloud cover was 51 µmol per m2 per s, and the reduction was 44 µmol per m2 per s in July. While this is a relatively small daily reduction, the impact of lower photosynthetic photon flux density is cumulative.

A corn field is seen next to a soybean field in Orrville, Ohio. Hanging over the corn and soybean crops is a cloud of wildfire smoke.
Figure 4. Wildfire smoke over corn and soybean fields in Orrville, Ohio, July 17, 2026.

What Conclusions can be Made About the Impact Smoke has on Corn and Soybean Production?

The effects of smoke may vary depending on the growth stage of the crop when such an event occurs. Sunlight needs to be captured by the plant to drive photosynthesis. While smoke may increase the diffuse light that can improve canopy light distribution, prolonged heavy smoke generally reduces total solar radiation and may increase ozone exposure, making net effects neutral to negative in many corn-production scenarios.

Under non-drought conditions, clear sunny days provide the best conditions for peak photosynthetic efficiency, thus maximizing yield potential. The authors of the Ohio study speculated that even the small reduction they saw would lower overall yield-potential of both corn and soybean.7 On the other hand, if the growing season is extended, the loss of PPFD earlier in the season may be overcome by a longer growing season.

As stated earlier, the effects of wildfire smoke on crop production are complicated, and there has not been much research devoted to this topic, so conclusions may be hard to find. There is much that still needs to be learned about the impact of wildfire smoke on crop growth as these events have the potential to become more frequent in the future.1


Sources

1Quinn, D. 2023. How does wildfire smoke impact corn growth? Kernel News. Purdue University. https://ag.purdue.edu/news/department/agry/kernel-news/2023/07/2023-corn-wildfire-smoke.html
2Archontoulis, S. and Licht, M. 2023. Wildfire smoke impacts on crop production. Integrated Crop Management. Iowa State University Extension and Outreach. https://crops.extension.iastate.edu/post/wildfire-smoke-impacts-crop-production.
3U.S. Environmental Protection Agency. 2025. Wildfire smoke – a complex mixture. https://www.epa.gov/wildfire-smoke-course/wildfire-smoke-complex-mixture
4McGrath, J.M., Betzelberger, A.M., Wang, S., Shook, E., Zhu, X., Long, S.P., and Ainsworth, E.A. 2015. An analysis of ozone damage to historical maize and soybean yields in the United States. Proceedings of the National Academy of Sciences. https://www.pnas.org/doi/full/10.1073/pnas.1509777112
5Yang, Y., Guo, X., Liu, H., Liu, G., Liu, W., Ming, B., Xie, R., Wang, K., Hou, P., and Li, S. 2021. The effect of solar radiation change on the maize yield gap from the perspectives of dry matter accumulation and distribution. Journal of Integrative Agriculture. Science Direct. https://www.sciencedirect.com/science/article/pii/S209531192063581X?via%3Dihub
6Hemes, K.S., Verfaillie, J., and Baldocchi, D.D. 2020. Wildfire-smoke aerosols lead to increased light use efficiency among agricultural and restored wetland land uses in California's central valley. JGR Biogeosciences. AGU. Advancing Earth and Space Science. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JG005380
7Lindsey, A., Lindsey, L., and Wilson. 2021. Hazy days…How does light influence corn and soybean? C.O.R.N. Newsletter. Agronomic Crops Network. Ohio State University Extension. The Ohio State University. https://agcrops.osu.edu/newsletter/corn-newsletter/2021-26/hazy-days%E2%80%A6how-does-light-influence-corn-and-soybean
Web sources verified 7-20-2026. 1114_264551

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