Drought In The Rear View

April 26, 2013 08:47 PM
Drought In The Rear View

2012 will have little impact on this year’s yields

Will 2012’s extreme drought drag down this year’s yields? Many farmers believe that drier-than-normal soil conditions will have a carryover effect on this year’s yields. But if USDA agronomical economists are correct, the 2012 drought will have a minimal impact on this year’s crops.

Paul Wescott, an USDA agricultural economist, presented the counterintuitive findings at the Agricultural Outlook Forum earlier this year. He and USDA’s Michael Jewison developed an agronomic model that accurately projected yields in eight corn-producing states and seven soybean-producing states from 1988 to 2012.

The pair found that yields are largely determined by growing-season weather conditions in a given year. The biggest factors in the success of corn crops are spring planting progress by mid-May, rain in June, and rain and heat in July. To gauge the impact of drought conditions during planting season, the economists evaluated overlaid data from the Palmer Modified Drought Index and cumulative monthly precipitation.

"In no case did we come up with a statistically significant effect," Wescott says. Though it’s important to monitor states with continuing drought, he adds: "It [previous drought] doesn’t appear to have an impact."

What does have a bearing is whether corn receives enough rainfall in June. A 2" shortfall, like the Corn Belt experienced in 2012, is enough to reduce yields by 20 bu. per acre. "Then we got a hot, dry July, which took away another 22.7 bu. per acre," Wescott says.

The model shows heat and moisture in July have the biggest impact on corn yields. "However, extreme weather deviations from normal in June can have larger impacts, as seen in 2012 and in 1988," the economists report.

The soybean model doesn’t include a variable for planting progress and uses average July and August weather variables, rather than just July weather. The model explains 80% of the variation in soybean yields.

"The model’s weather variables have lower statistical significance in explaining soybean yields than corn, likely reflecting the longer reproductive period for soybeans," according to the report.
The report is a sigh of relief for many farmers—there is hope for good growing conditions this year. 

You can e-mail Boyce Thompson at bthompson@farmjournal.com.

For more numbers behind the relationship between weather and corn and soybean yields, visit www.FarmJournal.com/drought_news

corn yield model

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