One perspective on high yield for 2014 U.S. corn and soybeans
With U.S. corn and soybean conditions near record good-to-excellent levels and the June acreage report behind us, market discussion is turning to the possibility of a high yield (see June 16 farmdoc daily article by Darrel Good, "Potential for U.S. Average Corn and Soybean Yields, available here). This article will try to add perspective to this discussion. While most will focus on the numbers, the author's focus is to illustrate methods that use historical yield data to assess what are high yields. It is important to understand that these methods will give different estimates of high yields over different periods of data. In short, the methods are data sensitive. In addition, other methods exist.
This study uses harvest yield per acre for states and the U.S. over the 30 crop years from 1984 through 2013. Selection of the study period is a critical factor. A longer period means more observations and thus, usually, better statistical properties for the analysis. But, it also tempers the importance of more recent yields, which may contain more information about current yield technologies and weather patterns. Trade-offs exists and reasonable analysts can select different periods. The author likes 30 years as a balance between statistical properties and the potential information value of more recent yields. Source for the yields is the U.S. Department of Agriculture (USDA), National Agricultural Statistics Service (NASS) Quick Stats website, available here.
The base method starts with estimating a linear trend line yield using linear regression techniques. Figures 1 and 2 presents the annual U.S. harvested yield per acre for corn and soybeans, respectively, from 1984 through 2013. The figure also contains the linear trend line estimated by regression. A key attribute of a trend line is the slope of the line. For this particular analysis, the slope is interpreted as the annual rate of increase in yield from 1984 through 2013 given a linear time line and the use of regression techniques. Given these assumptions, the U.S. yield of corn increased 1.73 bushels per acre per year while the U.S. yield of soybeans increased 0.43 bushels per acre per year (Figure 3). The yield of corn increased 4 times faster than the yield of soybeans over this period.
High Yield Estimate 1
The first set of estimates is based on asking what the existing record U.S. yield is. They are 164.7 bushels per harvested acre for corn and 44.0 bushels per harvested acre for soybeans. Both occurred in 2009.
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