Every year summer comes and we in the agriculture industry dread the days that start to creep up on 30 degrees celcius. This year with drier conditions the across the prairies we are likely to see extreme heat cause even more significant yield reductions. But what exactly is the reasoning for this? Is every crop impacted the same? Is there anything that can be done to mitigate this?
The first reason high temperatures begin to degrade our yields is very simple; The moisture we do have goes from helping to drive yield, or from an offensive job to helping a plant stay cool, or to a defense system. This is significant as a plant tries to conserve moisture it has to take focus off of dividing cells and driving yield to ensuring it has the resources necessary just to make any seed at all.
The next is that as temperatures increase, plant respiration starts to use more photosynthates, or sugars, than it is capable of producing during the day which again takes scarce resources away from driving yield. As plants move into the reproductive stage their demand for sugars and water increase dramatically which is part of the reason you will generally see flowering crops impacted more than those still in the vegetative phase.
Lastly, in the flowering stage our cool season crops are producing pollen; pollen formation tends to be very sensitive to temperature influxes, which leads to poor seed set and abortion.
In general the crop that gets the most attention during hot conditions is canola, but anything from wheat, to peas, to barley to lentils is negatively impacted by these warm conditions. Canola just tends to have the most obvious “blanking”, but don’t be fooled all of our crops take a yield hit when temperatures rise. Even in the days following high temperatures there can still be penalties to yield.
A crop can have a “hangover” effect as it tries to bounce back to regular physiological functions, just as any of us can be sore for numerous days after a strenuous physical activity. This can make the yield impact bigger than what one would initially think. 30 degrees C often gets noted as the point when we will see issues arise, but the reality is that some of our crops can see yields begin to decline at temperatures as low as 18 degrees! There is one other thing to factor in: microclimate. You often hear about this in relation to disease, but it makes a difference for environmental stress. The canopy can actually be cooler which means that even though it may be 34 degrees in the air, but 28 degrees in the canopy which will decrease the stress put on the crop!
Is there anything one can do? While there is no way of entirely eliminating temperature stress, we can help our crops better manage high temps. Starting your crop off with a well rounded, balanced fertility package creates healthier crops that can push through high temperatures. Using variable rate technology you can identify where your high yield zones are in the field and give them the nutrients they need in the start of the season to better tolerate environmental stress. Second, some studies have shown certain crops respond well to foliar boron in times of high temperatures. Thirdly, some active ingredients within the group 11 fungicide family have been shown to help a plant better tolerate warmer conditions than those that went untreated. There are other ways to help manage heat stress, but they involve different practices or may be more long term strategies.
Understanding the principles behind heat stress sets us up for what to be expecting and helps drive innovative practices that may help crops yield better under high temperatures in the future.