The crucial factors determining how a crop will yield are the moisture and heat at a specific stage of development
In the fall of 2017, growers and crop forecasters were worried in Western Canada.
Soils were extremely dry in many parts of the Prairies, especially southern Saskatchewan, and there were fears of disastrous yields in 2018.
The fears, it turned out, were overblown. The average canola yield was around 40 bushels per acre and spring wheat yields were around 50.5 bu. in 2018. Those numbers are around the five-year average in Western Canada for both crops.
Such yields in the growing season following a dry year are not surprising, said Eric Luebenhusen, U.S. Department of Agriculture meteorologist, because fall drought is a poor predictor of crop yields all over the Northern Hemisphere.
“One of the things I’ve learned is you have to take (crop) outlooks, at this point (winter), with caution,” said Luebenhusen, who spoke at the U.S. Department of Agriculture outlook forum, held in late February in Washington, D.C.
Luebenhusen monitors climate and crop conditions in Europe, the Middle East and North Africa for the USDA. After studying the massive region for a number of years, he’s learned that fall conditions have a minimal impact on yield.
As an example, conditions were incredibly dry in northern Morocco in the fall of 2017. There were dozens of media reports on the drought and how 2018 would be a horrific year for Moroccan farmers.
“It was the driest autumn on record in Northern Morocco. The vegetative health index … was absolutely dreadful,” Luebenhusen said.
“(But) if you want to know where the wheat yield ended up — it was a record (high).”
Luebenhusen has noticed a similar pattern in Ukraine, Turkey and other parts of the world. There is almost no correlation between a fall drought and crop yield the following summer.
What does matter, though, is the moisture and heat at a specific stage of crop development.
“It’s flower for grains and late flower and early fill for oilseeds,” Luebenhusen said.
“Statistically, rainfall doesn’t seem to matter that much…. That doesn’t mean rain is bad; you need moisture to grow the crop. But it’s the right time (for) moisture and cool weather during that flower and fill. (That) seems to make or break the yields in these crops.”
In other words, timely rains and timely temperatures are the critical predictors of crop yield.
Luebenhusen isn’t alone in his observation. Dale Cowan, senior agronomist with Agris Cooperative in Ontario, has witnessed the same phenomenon in soybeans.
“August rains make beans. I don’t care what beans look like in June and July, as long as it rains in August during pod fill,” Cowan said.
“It’s amazing how much … yield you can put on in August.”
To test out his theory, Luebenhusen has developed a model to measure the relationship between crop yields and the conditions at flower or fill.
The idea is to take crop stage information and track the weather during the critical crop stage. As an example, calculate the number of days of potentially damaging heat while a crop is flowering in July, “rather than (just) saying it was hot in early July.”
Luebenhusen has been testing the model to see if it’s a reliable predictor of crop yields in Europe, northern Africa and the Middle East.
So far “it’s lined up with what we expected,” he said, but work on the model will continue.
While fall drought isn’t a good predictor of crop yields, it’s not meaningless, Luebenhusen said.
It can affect the amount of seeded acres and there are cases where soils don’t recover from dry conditions in the fall.
“But if you’re going to bounce back from a condition, it’s fall drought.”
