In addition to USDA lowering the 2019 forecasted U.S. corn yield by 1.2 bushels per acre (bpa) to 168.2, they also issued some figures for corn plants per acre and number of ears per acre for ten objective states and the weighted 10-state figure for both the number of corn plants per acre and ears per acre.
This graphic shows the 10-state objective corn plant population in plants per acre on the left hand axis vs. the implied ear weight in pounds per ear on the rght hand axis.
With the harvested acreage from each of the ten states along with their respective yields, we are able to calculate the 10- state weighted yield (shown in the yellow boxes).
The calculated 10-state weighted ear count is 28,649, the same as USDA calculated, and the lowest since the 28,275 figure seen for 2012, compared to the all-time high of 29,100 for the final 2018 figures.
In its crop production report, USDA furnished a graphic showing the weighted ears per acre for the 10 states vs. the implied ear weight for the past number of years.
For every year from 2013 through 2018, the final USDA ears per acre figure was lower than reported in September.
If history holds, the January 2020 crop production report should show the ten-state ear count below 28,650.
The other factor in calculating yields is the ear weight, but as opposed to plant populations that have continually increased over time, ear weights are more reflective of growing conditions during the year.
A favorable season featuring timely plantings along with ample moisture and average to below average temperatures tends to produce a bigger or heavier ear than a season characterized by late seedings along with dry conditions and heat.
We have calculated the 10-state implied ear weight as 0.3371 pounds/ear, the lowest since 0.3300 in 2015.
Using the formula 10-state weighted yield (= implied ear weight * # of ears/acre) /56 lbs/bushel results in an objective ten-state yield of 172.5 bushels per acre, the lowest since 161.5 bpa seen in 2013.
If the implied ear weight moves lower in the next few reports, combined with the likely downward ear population/acre figure, it should result in lower yields than the 168.2 bpa figure given last week.