Continuing La Nina Weather Pattern Suggests Lower Corn Yield

Continuing La Nina Weather Pattern Suggests Lower Corn Yield

If La Nina doesn't disappear by June 1, the U.S. average corn yield could end up as low as 147 bushels per acre in 2011, way below the trend line yield of 162 bushels per acre, says ISU's Elwynn Taylor. In 2010 farmers harvested a U.S. yield average of 152.8 bushels per acre.

The 2011 planting season is off to a crazy start. "But it's no more crazy than what we should expect when we have a La Nina spring," says Iowa State University Extension climatologist Elwynn Taylor.

When did we last have a strong La Nina event and weather pattern in the spring? "The last time was the spring of 1974," he says. "Not everyone remembers those crazy springs—when it's very warm and then very cold, and then very warm and then very cold again."

Such a weather pattern can play havoc with getting crops planted on time. But to make it even rougher for planting crops, the rain does the same thing as the temperature—going back and forth. "We'll have a dry period, then a wet period, then a dry period, then a wet period," notes Taylor. "It doesn't give you much opportunity to get the corn planting done on time. That's what La Nina does when it keeps this type of weather pattern going through spring and well into summer. That's what the current La Nina is doing in 2011."

Hopefully, first half of May will stay favorable for crop planting

Is the next dry period that's hopefully coming up this week or next week going to last long enough to allow farmers to get a lot of fieldwork done and planting completed? "Right now, according to the National Weather Service forecast, the answer to that question is yes," says Taylor. "But looking at what's happened in the past, I'm not too sure. However, at least there is some hope it'll stay dry enough during a number of days in the first half of May 2011 to allow farmers to get their corn planted. 

We've seen some very severe weather this spring in Iowa, and elsewhere in the U.S. this spring. Earlier in April over a dozen tornadoes struck western and northwest Iowa and did a lot of damage. And last week tornadoes across the southern U.S. caused severe destruction, especially in Alabama and Mississippi, and also some in Tennessee, Kentucky, North Carolina and Virginia. Not just destroying homes and buildings but last week's tornadoes across the south killed some people too.

La Nina event brings greater chance of severe weather this year

Is this severe early spring weather and tornado activity related to the La Nina weather event?  Taylor says, "When we have a La Nina event occurring and a La Nina weather pattern, there's a greater chance of severe weather. Also, when we have a La Nina occurring with very warm water in the Gulf of Mexico, the chance of having severe weather and tornados almost doubles. The water in the Gulf is warmer than usual this spring."

He adds, "With the kind of weather year we're in, as we go on in 2011, it won't just be a greater risk of tornadoes and severe thunderstorms, but it will likely include hurricanes too. That's what usually happens under these kinds of conditions. So be forewarned on this."

Considering late start, 2011 corn yield will likely be below trend line

As the 2011 calendar has flipped to May, La Nina is still in place. Has that made any change in Taylor's yield forecast? "It is becoming more likely that the national corn yield average for the U.S. in 2011 will be below the long-term trend," he says. "The continuing La Nina event has been with us long enough now that I can see there is almost no way it can be gone in time to not do some damage to 2011's corn crop."

Taylor says, "We are now looking at a 70% chance of being below the trend line for U.S. corn yield in 2011." That means somewhere under the 162 bu. per acre mark, which is the trend line yield. The market is assuming that as well, as you look at the high corn prices the market is trading at today. However, the market is still trading at a higher yield level than would be most likely in a La Nina year.

"I do expect La Nina will be a negative factor affecting the U.S. corn yield average this year," he says. "And if La Nina continues on further into summer, as it appears it might, if it is still here at the end of July, it could also negatively affect the national average soybean yield. But right now we're not making any comments on U.S. soybean yield prospects, because we're assuming La Nina may be gone by the time bean yields are most vulnerable to unfavorable weather, which is during pod-filling in August."

U.S. corn yield average may range from 147 to 154 bu. per acre

So what's Taylor's best guess on corn yield for 2011? If the La Nina is not really dropping in strength and it's still here 30 days from now—if it's still here June 1—the yield number would be 147 bushels per acre for the U.S. corn yield average in 2011. On the other hand, if the La Nina is fading away rapidly, Taylor thinks the yield could end up somewhere between 147 and 154 bushels per acre.

Retired ISU Extension economist Bob Wisner also expects the 2011 yield to be under the trend line. "We have to make some adjustments in yields because much of the increase in intended corn acres this year is outside the heart of the Corn Belt. It's in the lower-yielding areas," says Wisner. "And now, wet weather in April in the Dakotas and part of Minnesota is a consideration because those intended corn acres won't all get planted to corn.

Using his own yield calculations and Wisner's price forecast, Taylor has updated his "risk wheel" showing probabilities for yields and prices according to possible scenarios for this year's U.S. corn crop.

It is on www.twitter.com/elwynntaylor.

TAGS: USDA Extension
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