Source: FARM DOC DAILY, UNIV. OF ILLINOIS, 5/10/17


In the farmdoc daily articles of April 19, 2017 and May 3, 2017 we began to address the potential reasons behind the observation that U.S. average soybean yields in 2014, 2015, and especially 2016, were well above the long-term linear trend values for those years. We found that yields appear to have actually increased at an increasing rate over the last several years rather than at a constant rate in bushel terms (Figure 1). In other words, a quadratic equation provides a moderately better fit to U.S. average yields from 1960 through 2016 than does a linear equation. We also found there is an interesting spatial pattern in trends across states and by production practices. It turns out that a linear trend is still the best fit to actual yields for many states in the U.S. However, a quadratic trend provides a better fit than a linear trend for a number of states, particularly in the Southeastern portion of the U.S. and in Nebraska. We also find that yields on irrigated production have been increasing at a faster rate than for non-irrigated production. The purpose of today's article is to directly examine whether the non-linearity in U.S. average trend yield for soybeans is driven by trends in the Southeast, Nebraska, and irrigated production.

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