Expectations of high corn yields for 2014 are a result of generally favorable growing conditions to-date and on the high percentage of the U.S. corn crop rated in good or excellent condition.
Scott Irwin and Darrell Good from the University of Illinois researched the summer weather conditions that contribute to high U.S. corn yields with comparisons to 2014:
HISTORICAL CORN YIELDS
The graph included plots yields from 1960 through 2013 with the trend line yield. The U.S. average corn yield increased by an average of 1.8 bushels per acre per year during this time period. The six years since 1960 with the largest positive difference between actual yield and trend yield in bushels are 1972, 1979, 1982, 1994, 2004 and 2009. Yields in those six years were 11.1 to 18.8 bushels above the calculated trend with an average difference of 14.1 bushels. Yields were 9.4% to 15.2% above trend with an average of 12.3%.
RAINFALL AND TEMPERATURE
The summer weather conditions in those six years that contributed to the very large U.S. average corn yields relative to trend were identified. During those six years, June was slightly drier than average and July and August were slightly wetter than average. For those same high yielding years, temperatures averaged 1.0 degree below the long-term average in June, 2.0 degrees below in July and 2.2 degrees below in August.
High U.S. corn yields have been associated with
summer precipitation that was near to slightly
above average and summer temperatures that
were well below average. As expected, decline in
yields is steep for low levels of precipitation. Cool
weather slows down the maturation of the corn
plant and, therefore, provides a longer period for
adding dry matter weight to each kernel of corn.
PROJECTING 2014 U.S. CORN YIELDS
So far this year, June precipitation was well above average and temperatures were not excessive, but were above average. Early U.S. July weather was very favorable with below normal temperatures and precipitation near normal. Should such weather continue, a very high average corn yield would be expected.
With high current crop condition ratings, the U.S. average corn yield is expected to be above average. With an average trend line yield of 159.5 bushels per acre, an average yield increase of 14.1 bushels per acre for the past six top yielding years would result in an average US yield of 173.6 bushels per acre. Using an average yield on top yielding farms of 190.0 bushels per acre, increased by the average of 12.3% increase in top yields, the result is a 213.0 bushels per acre yield.
Many, including our Ag Services Department, are
projecting yields on top farms in excess of 213.0
bushels per acre. However, keep in mind there is
no historical precedent for an extremely high U.S.
corn yield during a year with well above average June precipitation. We also have August weather
to consider, and an early frost would curtail yields,
especially in the Northern Corn Belt.