Crop Comments: Ontario wildfires – Déjà vu all over again

Baseball Hall of Famer Yogi Berra once said, “It’s déjà vu all over again.” This phrase linked the French term déjà vu, meaning “already seen,” to the English phrase “all over again,” creating a humorous repetition. Much of the Northeast has recently experienced a major wildfire smoke invasion, compliments of our Canadian neighbors to the northwest. Humorous doesn’t describe the impact of all this smoke on human health, as well as that of animals and crops.

Flash back three years to what many journalists referred to as “Big Burn 2023,” which blanketed 11 provinces and all the states bordering Canada with noxious particle-laden smoke. By July 16, 2023, 4,147 fires had torched almost 39,000 square miles. International help rushed to help quell this disaster, as some of its smoke was transported by trade winds to western Europe.

According to Canadian Public Safety Minister Bill Blair, “These conditions are unprecedented. Due to climate change, similar extreme weather events may continue to increase in both frequency and severity across our country.” Blair stressed that “due to these weather-related anomalies average temperature readings have been warmer and drier, raising wildfire risk, as vegetation tends to become tinder under these conditions. Wind from a passing cold front, during the week of May 18, 2023, intensified the problem.”

The big question, agriculturally, was how such misbehaving climate affects crop production. Crop researchers at Purdue in Indiana answered that question with another: “How does wildfire smoke impact corn growth?”

One of those researchers (Dan Quinn, Purdue agronomy professor) wrote that in late June 2023 air quality warnings were issued throughout Indiana due to smoke caused by Canadian wildfires. Such smoke resulted in a noticeable haze and reduced direct sunlight. Quinn said the haze and reduced air quality from wildfire smoke can result in both negative and positive impacts on crop growth. The first negative impact is a reduction in light availability, which can reduce crop photosynthesis. During the week of June 26, 2023 (when local air quality concerns were the greatest), average solar radiation was decreased by 32% compared to the week prior.

Quinn explained that atmospheric wildfire smoke can reflect portions of incoming sunlight, reducing the total amount available to plants. Reductions in light availability from wildfire smoke are more likely to impact corn than soybean. This is due to corn being a C4 photosynthetic crop, having a higher light saturation point (at which further ultraviolet light increases do not benefit photosynthesis). Soybean is more susceptible to changes in carbon dioxide levels.

The second negative impact caused by wildfire smoke is increased ground-level ozone, which can be harmful to human health and crop growth. Wildfires can emit various air pollutants, which can form ozone when reacting with sunlight. Ozone can harm both corn and soybean by entering plants through their stomates, thus causing harm to plant tissue during respiration. Both reduction in sunlight and increase in ozone can reduce photosynthesis. When this happens, corn may be inclined to remobilize carbohydrates from the stalks later in the season in order to satisfy grain-fill requirements. Such developments increase the potential for weak stalks – and thus lodging – prior to harvest.

However, wildfire smoke in the atmosphere can also actually benefit crop growth. One positive effect is that not only can wildfire smoke reflect sunlight, it can also scatter sunlight. Scattering light allows this radiation to penetrate deeper into the crop canopy and increase plant photosynthesis. When light is scattered and direct sunlight is reduced, this can also lower leaf surface temperatures, which can benefit crops under drought stress. Lower leaf surface temperatures can reduce the amount of transpiration (water movement and evaporation from the plant) needed to cool the plant and reduce total water stress. Corn is more susceptible to the effects of wildfire smoke during the grain-fill stages.

Throughout growing season 2023, Great Lakes states experienced the loss of two to three weeks’ worth of functional growing degree days. As these climate-altering events are expected to become more frequent, it’s important to pay attention to them in the future. Some crop researchers now recommend that plant breeders develop corn varieties that are less susceptible to reduced solar radiation. Goaded by even more solar radiation loss in their country, Chinese researchers in recent years have begun breeding for corn plants that can thrive with less effective sunshine.

This July 18, I found an eye-catching article titled “A supercharged El Niño is threatening more deadly heatwaves – and Americans are ignoring the risks”. Author Julia Musto’s article addresses the human health threat posed by climate change. Her story makes no mention of crops. But to my way of thinking, it’s only a small mental leap from Canadian Public Safety Minister Bill Blair’s lead-in quote (earlier in this column) to another. Those words came from Florida meteorologist Jeff Berardelli: “An historic, supercharged global El Niño event isn’t going to make matters any better – with more intense heat domes forecast this year on top of rising temperatures linked to climate change.”

by Paris Reidhead