Hazy Days

Each year has its unique growing conditions. I think 2023 has said “hold my beer”. Not only did we confront a widespread drought, but we are also dealing with the haze, smoke, smog from the Canadian wildfires. Combined with a little humidity from a typical Midwest summer, and we have some fun situations.

Is this good, bad, or neutral for our crops? We will give you a typical agronomist’s answer: it depends, or we are not sure. In an agronomist’s defense, how many times have we seen this to understand how it may affect crop plants? To an extent, what we do understand are plant systems. Combining this with what we think we understand about light and light quality, we can form some points to ponder.

Smoky-filled skies are hard to replicate. We can; however, look at data from cloudy days and from shade plots. Corteva research on photosynthetically active radiation (PAR) indicates that PAR can be reduced in direct relationship to cloud cover. The most significant growth stage is during the ever-critical pollination and grain fill periods. The early-June light quality issues may not have been as impactful as what we are receiving now in late July. See the full article on our Dairyland Seed website under Inside Pride blog https://www.dairylandseed.com/articles/solar-radiation-in-corn-production/

Figure 1. Daily PAR received in Johnston, IA under rainy, cloudy, and sunny conditions on four different days in summer.

Research from Purdue University focuses on what the hazy days did for light radiation in June. For the week of June 26, 2023, light radiation decreased by 32 percent. According to the bulletin “How Does Wildfire Smoke Impact Corn Growth” by Dan Quinn at Purdue University, smoke-filled skies can reduce incoming light and have a greater effect on corn as it is a C4 plant. These types of plants saturate light at a higher level, so more light is needed. Soybeans may not have as much of an impact as they are C3 plants. Quinn also notes higher Ozone levels which can negatively impact yields.

Is there any good news? Quinn indicates smoke could reflect sunlight. By doing so it could help light penetrate deeper into the crop canopy increasing the photosynthetic rate. Quinn also adds that reduced light can keep plants cooler -- adding to yield.

For the complete article see https://ag.purdue.edu/news/department/agronomy/kernel-news/2023/07/2023-corn-wildfire-smoke.html

In summary, the following positive and negative effects of smoky days

Low light quality can reduce yields, especially grain fill, during the R stage of corn.
Scattered sunlight may be a positive in penetrating crop canopy.
Cooler temperature from smoky days may be a benefit.
Soybeans may be less affected.