Fundamentally Speaking
Joel Karlin DTN Contributing Analyst

Wednesday 09/26/12

Illinois Derived Soybean Pod Weight vs. August Temps

Soybean futures have tumbled close to $2.00 per bushel from the all-time highs set near $18.00 per bushel at the beginning of September.

One of the reasons cited are widespread reports of soybean yields coming in higher, sometimes significantly so from earlier expectations.

This could be resolved when the October crop production report is released but for now the current USDA estimate is 35.3 bushels per acre (bpa), down from 36.1 bpa given in the August report.

This is the lowest national yield since a 33.9 bpa yield was posted in 2003. Illinois is one of the largest soybean producing states in terms of yield and production but very stressful weather this summer has resulted in a 2012 yield of 37.0 bpa.

Thisties 2003 for the lowest yield since 1988, another infamous drought year when the IL yield came in at 27.0 bpa.

Soybean yields are based on the number of soybean pods per acre and the average pod weight.

The USDA in its September crop production report indicated for the top soybean producing states the number of soybean pods per an 18 square foot plot and using a formula one can derive an implied soybean pod weight.

The USDA reported that there were 1,466 pods per an 18 square foot area for Illinois and that is the lowest number of pods per 18 square feet since 1,450 seen back in 1991.

Using this pod number and yield the Illinois derived soybean pod weight is 0.284 grams per pod.

This is actually higher than the past two years and above the 1990-2011 average.

It appears that the low soybean yield is based more on the very low pod count as opposed to the pod weight.

Nonetheless, we were curious about the impact of August temperatures on soybean pod weights and present the accompanying scatterplot.

The R squared indicates that August temperatures explain a little less than half the variability observed in soybean pod weights.

Note however, that since 1990, the year that saw the lowest August Illinois temperatures 1992 also had the highest soybean pod weight while the year with the highest August temperature had the second lowest soybean pod weight.


Posted at 9:18AM CDT 09/26/12
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