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Fine Tuning Corn Yields
Monday, September 16, 2019 3:12PM CDT
Fine Tuning Corn Yields 09/16 15:10
Yield Numbers Are Still a Moving Target
Before analyzing the Sept. 12 USDA reports, we must first remember the
methodology they use, according to Alan Brugler, a DTN contributing analyst.
USDA rolled out another crop production report Thursday, Sept. 12, with the
companion World Agricultural Supply and Demand Estimates (WASDE). Unlike the
two most recent editions, this report was a lot closer to trade expectations,
generally going in the same direction. Estimated planted and harvested acres
were left unchanged from last month. There are still questions about whether
permitting corn to be grown as a cover crop will result in a higher
abandonment/silage number, resulting in fewer acres harvested for grain.
National Agricultural Statistics Service (NASS) indicated that it might not
resolve that question until after the big post-harvest farmer survey in
December. Producers are asked to specify silage acres in that survey, with
results released in January on the mega report day.
NASS cut projected national average corn and soybean yields, which most
producers had argued was necessary. The average soy yield was reduced 0.6
bushels per acre (bpa) to 47.9 bpa. The average yield for corn was trimmed 1.3
bpa from last month to 168.2 bpa. Projected average corn yields were reduced
from last month in 19 states, and increased in four. In the garden spot of the
U.S. this year, the Nebraska, Iowa and Missouri yields were left unchanged from
last month's estimates. Now the fine-tuning begins. Out of the past 20 years,
NASS has been too low on final yield in the September report 11 times and too
high nine times. The average miss is 3.1% or 269 million bushels (mb). There
are a number of ways to get from September to the final number, however.
First, we have to remember the methodology NASS is using. The primary horse
the analysts are riding is the farmer survey, with 9,624 completed surveys for
this September report. NASS fills in the data holes from the farmer surveys
with satellite data and with their own objective yield plots. There were 2,905
objective yield plots visited between Aug. 24 and Sept. 1. The satellites tell
you what crop is there, and via Normalized Difference Vegetation Index (NDVI)
can give you some correlation between the image and historical yield. Where the
satellite images pair up with ground observations, you can calibrate the
satellite data. This is the area where most of the ag and weather industry
satellite forecasts fall apart. They don't have enough ground truth samples
because they don't do as many farmer surveys or objective yield plots. The
latter is very important because they give you ear counts, ear girth and length
that are nearly impossible to measure from a satellite no matter how good your
Speaking of ear counts, they are down this year. Here are the September ear
counts per acre for the 10 states tracked for this purpose. None of them have a
record-high ear count, as late planting, poor soil conditions, compaction and
other issues took a toll. Final ear counts are usually lower than the September
number. Compare the Final 2018 to the Sept. 18 column for a general idea.
Per Acre Final Final Final Final Final Final Sept Sept Max
2013 2014 2015 2016 2017 2018 2018 2019
IL 30150 30100 30800 30450 30250 31500 31550 30300 31550
IN 29850 30450 29150 29250 28850 29750 30000 28900 30450
IA 29550 30150 30850 30500 30600 30800 31150 30250 31150
KS 22200 24000 23650 22450 22650 21700 22350 21550 24000
MN 30850 30950 30450 30250 30600 30800 30850 30050 30950
MO 27100 27900 26850 27150 27850 27300 27400 26950 27900
NE 25700 26200 26700 25400 25950 26800 27100 25850 27100
OH 28300 29600 29600 29600 29150 30300 30750 29850 30750
SD 25300 24450 25750 25450 25850 28050 28100 26450 28100
WI 28950 28600 28600 28750 28550 30450 30700 29850 30700
Average 27795 28240 28240 27925 28030 28745 28995 28000
This is the lowest ear count per acre since the 2012 drought. A quick and
dirty, unweighted average for the 10 states puts the ear count at 28,000 in
September, down 3.5% from last September. If ear weight was identical, you'd
expect yield to be 3.5% smaller, i.e. 170.34 bpa. This is only from 10 states,
and USDA is actually using something north of 28,100. National average ear
weights can vary from a little over .31 pounds per ear to a bit over .36
pounds. Number of kernel rows, kernel depth and ear length all enter into that
part of the equation.
With the exception of 2018, final ear weights were higher than the one used
in September. Since very few of the objective yield plots have been harvested
and sent to the lab yet, the ear weight for 2019 is derived from the farmer
survey/published yield and the ear count. Producers are basically saying the
grain weight is going to be the lightest since 2014 due to smaller ears.
To wrap up our little exercise, that yield number is still a moving target.
Just about all the data we have at our disposal suggests a below-trend yield,
but how much below is a question mark. The elephant in the room -- the delayed
maturity of the crop -- suggests we still have considerable risk of a freeze
hitting before all the crop makes it to black layer (maturity). That would hurt
grain weight by stopping starch deposition.
If something like that happens (the GFS and European models are in some
disagreement right now) we also have to remember that it does not typically hit
all states equally. If you get a 10% loss on a state that has 3% of U.S.
production, that is only a .3% hit on U.S. production.
It is a big deal if it is your corn, but otherwise not so much.
Alan Brugler may be reached at email@example.com
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