Smoke effects on Crop Development

 

Smoke from over 830 Canadian wildfires continue to cause hazy skies, poor air quality and breathing health concerns for those most vulnerable, especially in Northern Ohio, Northern Indiana, and Michigan. While the worst air quality concerns occurred 2-3 weeks ago, there is still an Air Quality Alert for this area. The smoke contains many fine particles which get in the lungs and exacerbate breathing problems. Elderly people, children and those suffering from any type of illness need to stay vigilant. The hazy skies and campfire-like smell may make the sunrise and sunsets more colorful, but they are dangerous for affected individuals. For these individuals; limit outdoor activity, keep windows closed, monitor the air quality index and monitor your breathing. Consult a doctor if experiencing difficulty. With the recent rains and weather patterns, the smoke and haze may start to diminish.
The effect of the Canadian wildfires on crop development has been minimal. The weather has been cooler lately and the haze causes minor reductions in sunlight. Ohio State University Extension data shows that while localized sunlight can dip temporarily, it rarely reaches the threshold needed to cause severe crop damage. It still has some effect on crops but not major.
The biggest change is that the smoke and haze reduces light intensity which can lower solar radiation. If it lowers it 30% to 50%, that can hurt yields, but most of the haze reduction in solar radiation was only short-term, not long-term. One benefit is that smoke particles scatter sunlight, and this allows the sunlight to “diffuse” or penetrate deeper into the crop canopy so lower leaves benefit from more efficient photosynthesis. This offsets some of the negative effects to sunlight leaf blockage on upper leaves.

The smoke and haze and aerosol particles can act as a barrier to heat so slightly lower peak temperatures may occur during the day. Most plants have peak photosynthesis between 68O F and 86O F. Lately the nighttime temperature have been much cooler which generally benefits corn. Ideal temperatures between 50O F to 65O F are good for corn. Below these nighttime temperatures, corn respiration (the conversion of glucose to energy) slows down at night.

The smoke and haze my delay crop maturity slightly. Cooler day time temperature may cause a slight reduction in accumulated growing degree days which may cause minor delays in corn dry-down and harvesting. The less intense heat is good for relieving moisture stress in corn. Cooler temperatures and less intense direct sunlight reduce leaf surface temperatures, giving crops relief during dry spells.

For soybeans, they are much more resilient than corn to high nighttime temperatures but suffer the same for low nighttime temps. The two low temperatures to be most concerned is below 50O F and frost (below 32O F. Usually, high nighttime temperatures above 86O F cause corn the most distress and may cause as much as a 40% reduction in yields.

Wildfire smoke also results in higher ozone levels which can damage plant issues and reduce overall plant productivity. Also, the fine smoke particles can block the stomata on the undersides of leaves that plants use to breath in gases (i.e. carbon dioxide) and exhale (i.e oxygen) for photosynthesis. This is the opposite reaction for humans.

So far, a wet spring and some late frost followed by a relatively mild summer (except for 1-2 weeks of hot weather) has yielded crops that look very good overall. Most forecasters put Ohio crops at near or slightly ahead of historical 5-year averages. For Northwest Ohio, crops are slightly behind due to wet spring weather and late planting. In my travels, I see about 25-35% of the corn looking excellent which was planted early and is well past tasseling and is silking and setting ears. But a lot of corn is just starting to tassel or just past tasseling. Typically, corn should tassel by mid-July but can go to early August like this year. We will need good weather to finish the crop.

While some areas are still wanting more rain, most crops look fairly good for this time of year (August). Usually, rain in August makes or breaks most of our crops. Rain makes grain if it falls in moderation. Hopefully with a little more rain in the forecast, we can have decent to above average crops this year.

For soybeans, most soybeans are blooming and are now starting to set pods. I see some excellent fields of soybeans but a good many, similar to corn; were planted later and do not have the height or the nodes yet. Some timely rains and moderate temperatures would benefit all our crops.