With over half of the U.S. corn crop already cut when the USDA started collecting their data for the October crop report, I am going to make the assumption that their latest yield number of 122 bushels per acre is pretty close to the final figure. With that in mind, I am going to give this definition to 2012 U.S. corn yield: a disaster. How did I come up with this definition? If one were to plot corn yields since 1960 versus the 1960-2012 linear trend (which I show above), only five times have we seen national corn yields in a given year fall more than 15 percent below that trend; it is that 15 percent deviation figure that I am using to define a “disastrous” national corn yield. The years since 1960 with the dubious distinction of producing those poor yields were:

• 1974 (82% of trend, due to late spring planting, July heat/dryness, and early frost);

• 1983 (78% of trend, due to July/August heat and dryness)

• 1988 (75% of trend due to late spring/summer heat and dryness)

• 1993 (83% of trend, due to major flooding); and

• 2012 (78% of trend, due to summer heat and dryness).

Obviously there were many other years with yield “disasters” on a national basis prior to 1960, but it gets more difficult to define exactly which years were “disasters” due to the lack of a trend in yields (from 1900 to about 1940) or just the beginning of a trend (from about 1940 through the 1950s). For 1900 through 1940 (a period when, if anything, yields trended LOWER due mainly to a lot of poor crops in the 1930s), I decided to use a definition of a yield “disaster” as any time that the national corn yield came in below 23 bushels per acre. Using that definition, the 1900 to 1940 time frame produced six years with national corn yield disasters:

• 1901 (18.1 bushels per acre due to summer heat and dryness)

• 1913 (22.7 bushels per acre due to summer heat and dryness)

• 1924 (22.1 bushels per acre due to a very wet and very cool summer)

• 1930 (20.5 bushels per acre due to summer heat and dryness)

• 1934 (18.7 bushels per acre due to summer heat and dryness)

• 1936 (18.6 bushels per acre due to summer heat and dryness)

It is the 1940 to 1960 time period when it is most difficult to determine the years with corn yields that were a “disaster”, with the early-mid 1950s being especially difficult. About 1953 to 1956 was a period in which heat and dryness in the summer in the Corn Belt was quite common (remember that our current drought is said to be the worst since 1956). Yet during that time, we had the second highest corn yield on record set in 1953 and 1955, and set new national corn yield record in 1956. Because of that, it is hard to label years like 1953, 1955, and 1956 as “disasters” in my mind. Thus, I am going to define just 2 years between 1940 and 1960 as yield “disasters” for the U.S. corn crop:

• 1947 (28.6 bushels per acre due to a wet/cool spring and August heat/dryness)

• 1954 (39.4 bushels per acre due to summer heat and dryness)

So there is my list…13 years since 1900 in which, by my definition, corn yields were a “disaster” (an average of one every 11-12 years). The question then becomes pretty obvious: what was the tendency for corn yields in the year after the “disastrous corn yield?

One point is clear right away just by looking at my list of years: a year with a national corn yield disaster has NEVER been followed by another year with a national corn yield disaster. Even during the very worst droughts ever recorded, which most people would consider to be those of the Dust Bowl days of the 1930s (when, by my defintion, we had three years with disatrous corn yields), we saw yields recover after the disastrous corn yield years.

Looking at the statistics more closely though shows that, not only are corn yields in the year after the corn yield disasters better, in most cases they were a lot better. Shown above are the 12 years since 1900 that followed the national corn yield disasters. Note that 1955 is the only year on the list when the year-to-year percentage increase in national corn yields did not reach double-figures. Only three years failed to score a year-to-year increase in yields of less than 20 percent, and half the years scored a year-to-year increase of more than 30 percent. How many of these years scored above-trend yields is impossible to answer due to the lack of an actual trend in yields during the early part of the 20th century. Note though the last three times that we had a disastrous corn yield, those years were followed by not just better yields but above-trend yields the following year. However, note that the odds would not favor an attempt at record-large yields next year, as that occurred only twice in the list of twelve years (and note that one of those years was 1994, one of only two years on the list when we did not have to recover from drought conditions of some severity…something we will obviously have to do for 2013).

CONCLUSIONS

My definition of a national corn yield disaster would be a yield that is 15 percent below the 1960-2012 trend. I would thus label this year’s national corn yield as a “disaster”, something that has happened (by my definition) only 12 other times since 1900. If national corn yields in 2013 are 15 percent or more below the 1960-2012 trend (which would equate to a yield of about 134 bpa or lower), that would be a scenario that would be unprecedented; a year with a corn yield disaster since 1900 has never been followed by yet another disaster the next year. Statistics show that corn yields in the years following a corn yield disaster have always increased, and in the vast majority of cases have increased by a big margin (sometimes reaching above-trend levels, but rarely reaching record-setting yield levels).

If you would like further details into this study, please feel free to contact us at craigs@weather.net