Production Blog

Do Your Own Yield Check

Pam Smith
By  Pam Smith , Crops Technology Editor
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Scouts will be counting next week to see how 2015 yields stack up. Why not head to the field and do your own calculations. (DTN photo by Pamela Smith)

DECATUR, Ill. (DTN) -- It would be easy for Kurt Line to mentally kill the corn crop this year. The farmer saw prolonged wet conditions early in the season that drastically reduced yield potential in the corn fields he farms in north west Indiana. He remains somewhat optimistic about soybean yields, but also knows what happens in his fields are but a drop in the proverbial yield bucket.

To avoid a myopic view of the yield picture, Line and his father, Elwood, pack up each August and head west to join about 120 other scouts as part of the Pro Farmer Midwest Crop Tour. For the better part of next week, the scouts climb in and out of pickup trucks and trudge into corn and soybean fields to pull samples in an attempt to estimate yields in South Dakota, Nebraska, Indiana, Ohio, Iowa and Minnesota.

DTN Markets Editor Katie Micik and I will be among those attempting to get a read on what this wild and wacky production year might yield. We already know variability will be the big story. See Katie's assessment, "Midwest Crop Tour Preview," in DTN Ag News.

Wednesday of this week, I attended the 360 Yield Center field day and watched farmer's frustrations as USDA report estimated the third largest corn crop could be coming to market. As a kick off speech, Gregg Sauder, founder and president of 360 Yield Center, spoke for an hour on the agronomic challenges of the 2015 season and what we've learned so far this year.

I fully expect to see evidence of some of the agronomic anomalies he discussed on the tour next week. For example, Sauder said the entire corn crop pollinated over a span of three days in 2014 compared to 7 to 10 days in 2015. Have you noticed extremely long silks in fields -- it's a clue that maturity could be somewhat erratic this year. I expect nitrogen shortages and tip back to be high on the list of what we find next week.

Even though Line's corn was hammered by water this year, he said the crop did pollinate. "However, we don't have a healthy enough corn plant to prevent kernel abortion in the coming weeks," he said. "Much of the corn is deficient nitrogen and has a shallow root system, so the recent dryness is also taking its toll on the crop.

"Fields with higher elevation or some slope look better," he added. "It seems like every year we talked about variability in the tour, but this year in the East, I would expect samples to be extremely variable.

"I have a little more hope yet on the beans if we could catch some rains. Don't get me wrong, bean fields have their share of drowned out spots and short beans, but they seem to be well podded for what they've been through." Soybeans are not measured for yield on the tour, but reports include the number of pods in a 3 ft. by 3 ft. square.

If I've learned anything over the past few crop tours, it is that yields from the road are almost always deceiving. Quit slamming those USDA numbers and go look what is in your field. It's also a good time to size up storage and transportation needs and do standability checks and disease evaluations for 2016 hybrid selection.

I interviewed Purdue University agronomist Bob Nielsen about yield sampling last year, and he reminded me that maturity is important in this process. "Once a [corn] field gets beyond the milk stage to the dough stage, it's ok to be doing yield checks because the kernels you see are still going to be there at harvest. Kernel abortion occurs around blister or milk stage," said Nielsen. The kernel milk stage occurs about 18 to 22 days after pollination is complete.

HOW TO COUNT THOSE KERNELS

There are several formulas for figuring corn yield, but here's a simple system used by Nielsen:

Step 1. Count the number of harvestable ears in a length of row equivalent to 1/1000th acre. For 30-inch rows, this would be 17 ft. 5 in.

Step 2. On every fifth ear in that sample, count the number of kernel rows per ear and determine the average.

Step 3. On each of these ears count the number of kernels per row and determine the average. (Do not count kernels on either the butt or tip of the ear that are less than half the size of normal size kernels.)

Step 4. Yield (bushels per acre) equals (ear #) x (avg. row #) x (avg. kernel #) divided by 85. In the past, a "fudge factor" of 90 was used as the average value for kernel weight, expressed as 90,000 kernels per 56 lb. bushel, but kernel size has increased as hybrids have improved over the years.

Step 5. Repeat the procedure for at least four additional sites across the field. Keep in mind that uniformity of plant development affects the accuracy of the estimation technique. The more variable crop development is across a field, the greater the number of samples that should be taken to estimate yield for the field.

Example: You are evaluating a field with 30-inch rows. You counted 29 ears (per 17 ft. 5 in. = row section). Sampling every fifth ear resulted in an average row number of 16 and an average number of kernels per row of 33. The estimated yield for that site in the field would be (29 x 16 x 33) divided by 85, which equals 180 bu/acre.

On the Pro Farmer tour, scouts walk past the end rows and count out 35 steps to determine where their sample begins. If, after 35 steps, they're in a ponded-out spot or area that won't make ears, the field goes into the data set as a zero. Scouts then count all the ears in 30 feet of two side-by-side rows. They pull the fifth, eighth and 11th ears to count rows around and measure grain length. They plug the data into a similar formula to estimate yield.

Follow us in the field next week on Twitter: @PamSmithDTN will be counting kernels and sees on the western portion of the tour. Katie Micik heads east and can be followed at @KatieMDTN.

Pamela Smith can be reached at Pamela.smith@dtn.com

(KM/AG)

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