Similar to what we did with corn, this graphic is a scatterplot showing the week 30 (around the 7/30-8/1 period) crop ratings for U.S. soybeans vs the percent that the USDA's August soybean yield forecast deviated from the 25-year trend of final yields.
We use our usual system where we weight the crop based on the percent in each category and assign that category a factor of 2 for very poor, 4 for poor, 6 for fair, 8 for good, and 10 for excellent and then sum the results.
The 2021 U.S soybean rating as of week 30 is 714 which is slightly below the 20-year average of 715.
Such a rating would project soybean yields to be 1.1% below trend.
This year's calculated 25-year trend is 50.2 bushels per acre (bpa) so this year's rating would project the August 2021 yield forecast 1.1% below trend or 49.7 bpa.
The USDA weather adjusted soybean yield projection this year is 50.8 bpa so that would equate to a yield of 50.3 bpa.
In the chart we also include a table that shows the change in the percent deviation from trend yield from the August to final yield projection and the week 30 crop rating.
As an example, last year's August 2020 yield of 53.3 bpa was 7.3% above trend but the final yield of 50.2 bpa was just 1.1% above trend, a net move of down 6.2%.
This shows that August and September weather can make a difference as an August yield forecast that is ether above or below trend can change in both direction and magnitude by the time the final crop year projections are released in January.
This is particularly so for soybeans where August is considered the critical month.
This also explains by the R squared of 50.6% is quite a bit lower than the corn figure of 76.4%.
Another consideration is that soybeans are more geographically dispersed than corn with more seeded in the Ohio Valley, Southeast and Delta where conditions have been superb and record yields from a number of states are likely.
The bottom line is that as of the beginning of August, it appears the 2021 US soybean crop is on track to attain trend or slightly below trend yields so question is what happens to the crop over the next two months and what one's calculation of a trend yield is.
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