Editor’s note: The following was written by Gary Schnitkey, University of Illinois Department of Agricultural and Consumer Economics, for the university’s Farmdoc Daily website Dec 11.
From 2013 to 2018, U.S. soybean yields have been above trend in all years, with an average yield-above-trend of 3.7 bushels per acre.
States have had different experiences with above-trend yields. Six states had an average yield-above-trend of more than 5 bushels per acre. Four states had average yield-above-trends of less than 2 bushels per acre.
In the December Crop Production Report, the National Agricultural Statistical Service reported the average U.S. soybean yield for 2018 as 52.1 bushels per acre. This is just a bit higher than the 2016 yield of 52 bushels per acre.
In this article, a trend yield is based on a linear regression using the 40 years of data previous to trend yield. The 1994 trend yield is based on the 40 U.S. yields from 1954 to 1993. The 1995 yield is based on 1955 to 1994 and so on.
Note further that trend yields are not declining in recent years. If anything, those trend yields are increasing.
U.S. yields have been above trend since 2012, the drought year. This six-year run has been remarkable in its length.
Moreover, yields have been well above trend in recent years. For example, the U.S. yield was 52 bushels per acre in 2016 while the trend yield was 45.9 bushels per acre. In 2016, the yield-above-trend was 6.1 bushels per acre, the largest value for all the years for which the value was computed.
The second highest level above trend occurred in 2018, when the actual average was 52.1 bushels per acre and yield-above-trend was 4.4 bushels per acre. The next highest value occurred in 2005 when the actual yield was 3.3 bushels per acre above trend.
From 2013 to 2018, U.S. yields averaged 3.7 bushels per acre above trend. To see if there was geographical variability in yield-above-trends, a similar analysis was conducted for each state for which sufficient yield data exists.
For each state, trend yields were calculated for each year from 2013 to 2018. Then the difference between actual yields and trends were calculated for each year. Finally, the average differences from 2013 to 2018 were then calculated.
There is geographical variability to the yield-above-trends. Six states had average yield-above-trends over 6 bushels per acre. All of these states bordered the Mississippi River and included Louisiana (8.2 bushels per acre), Mississippi (7.5), Kentucky (6.9), Tennessee (6.7) and Illinois (6.5).
There were also a number of states that had yield-above-trends less than 2.0 bushels per acre. These states included Michigan (2.0), Pennsylvania (1.8), Wisconsin (1.5) and North Dakota (0.3).
There are tendencies to the above geographical distribution. Southern states typically have higher yields, extreme northern states have lower yields, and states in the middle have more mixed resulted.
However, those tendencies do not hold for all states. For example, Texas in the south has a yield-above-trend average of 2.9 bushels per acre, considerably below the other southern states. Similarly, South Dakota in the north has a yield-above-trend of 6 bushels per acre, considerably above many of the other northern states.
An interesting comparison is the “I” states in the heart of the Corn Belt. Illinois, with a 6.5 yield-above-trend, is significantly above the U.S. average of 3.7 bushels per acre. Indiana has a 3.8 yield-above-trend, near the U.S. average. And Iowa has a 2.5 yield-above-trend, which is below the national average. States relatively close to one another in the heart of the Corn Belt had different yield experiences.
A combination of good growing conditions, continuing increases in genetic potential of soybean varieties and changes in farming practices likely contribute to high yields.
Southern states appear to have adopted farming practices that continue to lead to improved soybean yields. In Illinois, soybean management systems have changed with a move to earlier planting and use of seed treatments and fungicides.
Still, geographic patterns do raise questions. Why has Illinois’ experience of high yields differed from that of Indiana and Iowa? Why did South Dakota have better yields than states around it?
Further examinations of farming practices and weather in states with higher and lower yield-above-trends may shed light on those questions.