The Season for Determining Corn Yields is Underway
This article was originally published on May 31, 2012 and expired on June 30, 2012. It is provided here for archival purposes and may contain dated information.
The 2012 U.S. average corn yield
will be one of the dominant factors in determining the level of corn prices
over the next year. Expectations about that yield have started at a pretty high
level, but according to a University of Illinois agricultural economist, the
critical period for yield determination is just beginning.
"The small percentage of
the crop planted late this year suggests that the U.S. average yield will be
higher than if a normal percentage had been planted late, but the level of
yields is still to be determined," Darrel Good said.
Good said that a small
percentage of the crop planted late this year and the early condition of the
crop point to the potential for an above-trend yield in 2012, but the most
important part of the season is just beginning.
"The corn market will
continue to follow weather developments and crop condition ratings in order to
refine yield expectations," he said. "At this juncture, two important
developments may be required in order to maintain high yield expectations. The
first is some convincing evidence that the relatively long period (8 months or
so) of above-average temperatures is giving way to normal or below-normal
temperatures. The second is for soil moisture deficits in important areas of
the central, eastern, and southern Corn Belt to be eliminated."
A second piece of early
information relative to corn yield potential Good reported is the crop
condition rating provided in the USDA's weekly Crop Progress report. He said
there has historically been a positive relationship between the percentage of
the crop rated good or excellent at the end of the season and the U.S. average
yield relative to trend.
"Early crop condition
ratings are suggestive of yield potential, but ratings can, and do, change
substantially by the end of the season," Good said. "The first crop
condition rating of the season this year showed that 77 percent of the crop was
in good or excellent condition as of May 20.
"Since 1986, an average of
only 66 percent of the crop was rated in good or excellent condition in the
first report of the season," Good said. "There were only six other
years when the initial ratings showed 75 percent or more of the crop in good or
excellent condition. The rating at the end of the season was higher than the
initial rating in two of those years (1987 and 1994), and the U.S. average
yield was well above trend in both years. The rating at the end of the season
was below the initial rating in four of the six years. The average yield was
near trend value in three of those years when the final ratings showed 60 to 69
percent of the crop in good or excellent condition. The U.S. average yield was
well below trend in 1991 when the final rating showed 53 percent in good or
What do we know about yield
potential as the summer growing season begins?
The most important development,
Good said, is to date is the timely planting of the crop. There is a relatively
wide window of planting dates for maximum corn yield potential, with yield
penalties associated with late planting.
"Since corn-planting dates
vary considerably by geographic area, corn planting occurs over a period of
several weeks, and has been occurring earlier over time, there may be a number
of ways to characterize timeliness of planting on a national basis," Good
"For the period beginning in
1986, we defined late planting as the percentage of the crop planted after May
20 in the major corn-producing states that are included in the USDA's Crop
Progress report," Good said. "This year, only 4 percent of the corn
crop in the 18 major corn-producing states was planted after May 20. That is
the smallest percentage of the crop planted late during the 27-year period
Good reported that, on average,
18 percent of the crop was planted after May 20 from 1986 through 2011. There
were nine other years when less than 10 percent of the crop was planted after
May 20. In those nine years, the U.S.
average yield was within two bushels of the trend yield in five years.
Good said large deviations from
trend yield occurred in the early-planted years of 1987 (up 8 bushels), 1988
(down 29 bushels), and 1992 (up 16.8 bushels).
"These yield results are
not especially informative for developing expectations about the average yield
in 2012," Good said. "With all else being equal, the planting date may
be important for yield potential, but summer weather conditions ultimately
determine the level of yields."
In addition to yield prospects,
Good said the expected size of the 2012 crop will be affected by the magnitude
of planted and harvested acreage. The USDA will provide survey-based estimates
in the Acreage report to be released on June 29. New-crop corn prices are expected to remain
under pressure as long as large crop expectations prevail.
Source: Darrel Good, Professor Emeritus, firstname.lastname@example.org
Pull date: June 30, 2012