Wheat School: Heat takes a bite out of wheat


“It is hot!” says Peter “Wheat Pete” Johnson in this episode of the Wheat School. And that heat is taking a bite out of wheat yields.

Wheat is a cool season crop and does not like heat, so when temperatures start to climb yield can be impacted.

The most critical stage is at filling. It takes about 660 growing degree days (GDD) to fill the wheat head, on average. Short season varieties are maybe more around 600 GDD. What’s a growing degree day you might ask? Simply put it is the high temperature of the day plus the low temperature of the day, divide by two. A perfect day in a wheat crop’s life is an 18 degree C high, and a 10 degree C low — a far cry from summer temperatures in Ontario right now.

(See video for an example of the math and how that impacts the number of  grain-filling days, story continues below)

Eastern Canada, particularly Ontario, is getting some extreme heat lately, with daytime highs above 32 degrees C and nighttime lows at 22 degrees C.

As the number of GDD accumulate faster from all this heat, the number of grain-filling days shortens. A 26-day grain fill period versus the average 33-day grain fill period means less potential for yield. This is why sometimes those early seeded wheat crops can pay because their grain-filling period catches more of those cooler days, Johnson says.

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