Crop Tour Preview from the Head Scouts

August 13, 2009 07:00 PM

Pro Farmer Editors

USDA's first survey-based corn and soybean crop estimates revealed record combined ear counts in the 10 objective yield states (Illinois, Indiana, Iowa, Kansas, Minnesota, Missouri, Nebraska, Ohio, South Dakota and Wisconsin). We'll be in seven of those states this week on the Pro Farmer Midwest Crop Tour. Along with agronomists from Tour sponsor Pioneer, about 70 volunteer scouts will visit roughly 1,000 corn fields and 1,000 bean fields to assess yield potential of the 2009 crops.

It's all in the ears!

Those record combined ear counts in the 10 objective states scouted by enumerators from USDA's National Ag Statistics Service (NASS), however, are not consistent throughout those states. USDA's "Crop Comments," included with the Aug. 12 Crop Production Report, said ear populations in Illinois, Missouri and Wisconsin fell short of record levels. Ear populations are one of the most "trusted" pieces of data collected on the Crop Tour and are very easy to compare to past Tours. Without record average ear counts in Ohio, Indiana, Iowa, Minnesota, South Dakota and Nebraska (and a record ear count for all the samples collected), we'll have "an issue" with USDA's corn yield estimate of 159.5 bu. per acre.

Don't forget how to use Tour data!

After we wrap up a state, the Tour will release a calculated corn yield estimate for each crop district toured in each state based on the samples collected in that district, and a corn yield estimate for that state based on all the samples collected in that state. When you see the corn yield, don't forget to apply the "historical error" to the "raw" number. We know the yield calculated by the Crop Tour will be different than USDA's final yield estimate for each state. Fortunately, we know (on average) by how much.

Historical Error

Historical Error -- Tour Yield vs. USDA Final
(Average since 2001)
Avg. Tour Yield
Historical Error
South Dakota
7 States

Why the error?

Climate and crop maturity are factors, but where the Tour travels causes the bulk of the error. For example, we don't sample typically lower-yielding fields in far down-state Illinois or lower-yielding acres in central and northern Minnesota. As a result, Tour yields have typically been above USDA's final yield in those states. In Nebraska, about 60% of the corn crop is irrigated, but the mix of samples from Nebraska includes only about 40% irrigated fields. As a result, the calculated Tour yield is well below USDA's final yield. There are reasons for the errors and understanding why and how to adjust makes the Tour extremely valuable.

Most importantly, check the change!

We don't mind a "semi-direct" comparison to USDA's Aug. 1 yield estimates if it is done on a percentage basis. For example, USDA sees a 22.2% increase in Ohio's corn yield from year-ago (135 bu. per acre in 2008; Aug. 1 estimate of 165 bu. per acre for 2009). If the Tour yield is up more than 22.2% from year-ago, you'll probably hear PF News Editor and Eastern Tour leader Roger Bernard say something like, "It looks like USDA needs to find a few more bushels in Ohio." If the Tour yield falls short of a 22.2% increase, you might hear Roger say something like, "It looks like USDA got a little too aggressive with its Ohio corn yield estimate."

On soybeans... no yield, just pods

There are so many variables that must be considered when estimating bean yields. Too many to count on a Tour like this. But, we do count pods and calculate an estimate of pods in a 3X3-foot square. That gives us a good idea of how much of the "bean production factory" is up and running. Again, compare pod counts to year-ago to see "how much of the factory is in production."

And it's 'one big corn field'

Because we keep plot selection "consistently random," we're not worried about pegging the corn yield in each field we visit. It can happen, but only if scouts land in the "absolute average" spot of the field. It's much more likely to sample from the best, or worst, spot of any individual field. That's why it's important to get an adequate number of yield samples from "one big corn field" that stretches from Columbus, Ohio, to Grand Island, Nebraska, and from Montevideo, Minnesota, to Carlinville, Illinois. Samples from fields with poor, great and average yield potential balance out.

Sample along with us!

In each corn field, get past the end rows and go 35 paces down a main row. At the 35th pace, layout a 30-foot plot and count all the ears that will make grain in side-by-side 30-foot rows. (Average the number of ears). Pull the 5th, 8th and 11th ear from one row. Measure the grain length (not cob length) in inches (and average). Count the kernel rows around (and average). The calculation is simple: Average ear count in 30-foot row, times the average grain length in inches, times the average kernel rows around and divide that by the row width in the field.

Example: 45 ears X 6.5 inches X 16.7 kernel rows divided by 30-inch row =162.8 bu./ac.

Go to a "representative spot" in bean fields and measure 3-foot of one row. Count plants in 3 foot. Select three plants (at random) and count pods that measure at least one-quarter inch on the three plants (divide total by three to average). Multiply the number of plants in 3-foot by the average number of pods per plant and multiply by 36; divide by row width.

Example: 16 plants X 48 pods/plant X 36 divided by 15 inch row = 1,843.2 pods in 3'X3'

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