Fundamentally Speaking

History of Corn & Soybean Ratings Changes

Joel Karlin
By  Joel Karlin , DTN Contributing Analyst

Looking at various drought indicators, percent of normal moisture maps and temperature readings over average levels data it doesn't look like things improved on a national basis in any of these categories over the past two months and this is reflected in deteriorating U.S. corn and soybean conditions in the same time period.

This graph shows the week 34 rating for U.S. corn and soybeans on the left-hand axis vs. the percent change in rating from week 25 to week 34 or approximately around the beginning of July to the end of August on the right-hand axis.

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 corn rating as of week 34 is 712 which though the second lowest since 2013, is still above the 1999-2021 average of 709.

Back in week 26 the corn rating was 734 so over the past nine weeks ratings fell 22 points or 3.0% which is actually lower than the 1999-2021 average of a 5.5% drop.

Scatterplot studies continue to indicate that current corn ratings still imply a near trend yield or about 176.0 bushels per acre (bpa).

This year's week 35 rating and decline since week 26 seems to look a lot like 2013 where the week 26 rating was 738 falling 3.5% to 712 with final corn yields that season 1.7% below trend.

As for soybeans, the 2021 week 34 rating is 694 which is the worst rating for this point in the season since 2012 and the third lowest since 2005 and compares to the average 708.

Back in week 26 the soybean rating was 718, so over the past nine weeks, ratings fell 24 points or 3.3% which is actually a shade lower than the 1999-2021 average of a 3.5% decline.

The best analog for soybeans came just two years ago when the week 26 rating in 2019 was 702 falling just slightly to a week 34 rating of 696 with final yields that season just 0.3% below trend.

As in corn, week 34 scatter studies also indicating this year rating also implying close to a trend yield of 50.0 bpa.

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