1. This #FDD looked at sensitivity of soybean trend yield estimates for the US to different sample starting dates. Similar to what we did the week before for corn. farmdocdaily.illinois.edu/2020/06/how-se…
2. Here is the history of US average soybean yields since 1960. The question is when should we start our sample for estimating the the trend. Use the full 60 year sample to estimate the line shown. Sure looks like some kind of shift in the last decade.
3. We estimated linear trend regressions moving the start year ahead one year at a time. Then projected 2020 trend yield for each sample set. Here is what you get doing that.
4. Fascinating pattern. Longest sample, starting in 1960, gets you a 2020 soybean yield trend of about 47.5bpa. This increases to about 49.5bpa through the mid 90s. Then just takes off for the shortest samples. 2000-2020 sample = 50.3bpa.
5. Same information but still interesting to consider change in trend coefficient estimate for the different sample period. Trend estimate is 0.43 bushels/year for 1960-2019 vs. 0.66 bushels/year for 2000-2019. Remarkable increase in rate of growth in trend yields!
6. So, when estimating trend yield for US soybeans looks like we should use a recent sample or a non-linear trend like the one shown below for the entire 1960-2019. Either way trend for 2020 is a bit over 50bpa. Choose your poison (in terms of ending stocks).
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