While not entirely explaining increased yields for corn and soybeans over the past 15 years, one Ohio State University agricultural economist said statistical evidence on linear yield trends shows biotechnology could play a role.
Carl Zulauf, a professor with the Department of Food, Agricultural and Environmental Economics and the Ohio Agricultural Research and Development Center, studied yield trends for corn, soybeans and upland cotton, three crops most widely associated with the adoption of biotechnology. He then compared yield trends for those crops with 11 other crops for which adoption of biotech seed is virtually nonexistent.
"Biotechnology varieties first became available for commercial use in the U.S. in 1996," Zulauf explained. "By 2011, they accounted for 88 percent, 90 percent, and 94 percent of the acres planted to corn, upland cotton, and soybeans, respectively."
With 15 years of yield data to analyze, Zulauf chose to compare trends from the biotech-influenced era with yield data from years 1940 through 1995, noting that 1940 marked the year when the average yield of most U.S. crops began increasing, due in part to traditional breeding methods.
In evaluating the data, he discovered that only seven of the 14 crops exhibited a higher estimated yield trend during the 1996-2011 period than the comparison years of 1940-1995. The 7 crops are barley, corn, cotton, peanuts, rice, soybeans and sugar beets. In other words, of the non-biotech-influenced crops, only four of 11 exhibited a higher yield trend in the more recent of the two data sets.
"This analysis finds that, while the yield trend increased for all 3 biotech crops after 1996, the yield trend increased for less than half of the crops for which biotech varieties are of limited importance," Zulauf said. "This finding does not prove that biotechnology is the reason for the higher yield trend for corn, cotton, and soybeans. It only reveals that the evidence on linear yield trends is not inconsistent with such a conclusion."
He observed that over 10 years, the higher yield trend translated into a harvested yield that was 1.6 bushels, 0.6 bushels, and 69.1 pounds higher for corn, soybeans, and cotton, respectively. The addition to yield is 1 percent, 1.4 percent and 7.9 percent of the highest harvest yield observed for corn, soybeans, and cotton.
"So, for corn and soybeans, the increase in yield trend since 1995 is not large," Zulauf remarked. "The implications, of course, are subject to change with more years of data."
Zulauf's full report, including information on the statistical methodology used in his analysis, is available online at http://aede.osu.edu/biotechnology-and-us-crop-yield-trends. A companion paper, studying the common observation that biotechnology has also reduced variation in U.S. crop yields, is also available online at http://aede.osu.edu/biotechnology-and-variation-average-us-yields.