Yields Now Vary Less from Trend Lines

February 6, 2012 08:30 PM

Crop yields varied less from trend-line yields from 1996 to 2011 than from 1940 to 1995, according to an Ohio State University study. "While this study cannot preclude biotechnology as an explanation for the decline in yield variability observed for corn, cotton and soybeans, it suggests more universal factors are likely occurring," concludes the study, by economist Carl Zulauf and assistant Evan Hertzog.

One such factor could be that both biotech and traditional breeding methods have been equally
successful at creating varieties that reduce yield variation. A second such factor could be that weather was more favorable across the various U.S. production regions during 1996 to 2011 than 1940 to 1995.

To the extent that the decline in crop yield variability is permanent and not transitory, it generates benefits, Zulauf and Evans say. A more reliable supply reduces the size of stocks that need to be carried to assure an adequate supply of food before the next harvest, thus reducing the cost of food. A more reliable supply also enhances the ability to expand nonfood uses of crops.

"Nonfood uses, such as energy production, require large capital investments. Large capital investments are more economically viable when utilized at close to full capacity. A stable input supply increases the odds that a plant can operate at full capacity," the study says.

Using corn as an example, the study’s authors calculated the percent deviation of the actual yield from the estimated trend-line yield for each year. For example, U.S. average corn yield was 160 bu. per harvested acre in 2004. The linear trend-line yield estimate for 2004 was 144. The percent deviation is +11% (160/144). In other words, average yield in 2004 was 11% greater than the trend-line yield for 2004.

For all 14 crops studied, the variation from trend-line yield was lower during the recent 1996 to 2011 period than during the 1940 to 1995 period. The average decline in yield variation was –45%, with a range from –14% (sugar beets) to –67% (peanuts). Moreover, for 10 of the 14 crops, yield variation was smaller in the more recent period, with 95% statistical confidence. The four exceptions were barley, soybeans, sugar beets and wheat. The average decline for the three biotech crops was –43%.

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