Do a Yield Checkup

Preharvest Examinations Help Select Seed for Next Year

Ear length and kernel rows are two of the measurements needed for estimating corn yield. (Progressive Farmer photo by Pamela Smith)

It may seem counterintuitive, but Kurt Line enjoys going into harvest knowing what his crop will likely yield. Next year's hybrid and variety selection starts before grain goes in the tank for this manager of Churchill Farms, Lake Village, Ind.

"As I take samples, I also look for clues as to what might be limiting yield and how we might fix that for next year," Line says. "Soybeans are a little harder to judge than corn, but you can certainly take a look at how many pods are there and get a sense of what the yield might be."

EARLIER DECISIONS

In years past, growers didn't need to lock in seed choices until January or February of the planting year, but competition and early purchase discounts have moved that decision into fall. It also means seed company or university research trial data from the current year typically isn't available before the combines roll.

Purdue University agronomist Bob Nielsen reminds growers that while yield is important, documented consistency in yield performance is still key to success in selecting hybrids. "That's about how well a hybrid tolerates a range of growing conditions. Until the day comes [when] we can predict a season's weather accurately, we are dependent on trying to identify those hybrids that perform regardless of the weather," he explains.

JUDGE CAREFULLY

"Except for the newest hybrids, performance data from the previous year is useful for identifying consistent performers for your operation next year," he says. "Seek out summaries over many locations and avoid concentrating on single-site results. If a hybrid performs consistently well over many sites, then it likely will perform well on your farm in the future."

In addition to looking at how an individual hybrid yields, growers need to consider the yield data in comparison with a series of similar, competing hybrids. Once a group of consistently high-yielding hybrids has been identified, growers can filter them down further for traits that best suit their farm.

There are several formulas to check yields (see "Count Those Kernels"), but the important thing is to be in the field taking assessments. "Once a [corn] field gets beyond the milk stage to the dough stage, it's OK to be doing yield checks; the kernels you see are still going to be there at harvest. Kernel abortion occurs around blister or milk stage," Nielsen says. The kernel milk stage occurs about 18 to 22 days after pollination is complete.

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Kernel abortion can be caused by stress resulting from heat, drought or severe nutrient deficiencies. Tip fill also correlates with plant population -- grain yield is a balance between plants per acre and kernels per ear.

DISEASE CHECK

Nielsen says this August period is ideal for measuring disease susceptibility, such as Goss's wilt, Northern corn leaf blight and gray leafspot. Most seed companies bestow tolerance ratings for leaf disease, but keep in mind they use their own system, and numbers aren't consistent across the industry.

"Note simple things like overall plant height and ear height, and other characteristics that go into making up that hybrid," Nielsen adds. For example, some growers don't like high ear set because it can raise the stalk's center of gravity and contribute to lodging.

Harvest preparation should also include a walk through the fields to determine stalk strength. This could be particularly important this year in fields that have experienced considerable moisture stress.

Stalk strength can easily be evaluated using the push test, where plants are pushed 45 degrees (about 10 inches) from vertical at ear level. Plants that break following the push test are at risk for stalk lodging. Stalk strength can also be evaluated by pinching the lower stalk at the first internode above the brace roots. Hollow and deteriorated stalks will easily collapse when pinched.

PUSH TEST

University of Minnesota plant pathologists recommend at least 20 plants be pushed and pinched in five locations within a field. Fields with 10 to 15% or more of the plants failing the push or pinch test are at risk for severe stalk lodging and go to the top of the harvest list to prevent downed corn.

Preharvest yield checks help determine storage needs, too. "Scouting in mid- to late August also helps me feel a little more comfortable marketing," Line says. "It's a lot easier to be confident of what percentage sold you want to be if you know a realistic potential

of the crop."

COUNT THOSE KERNELS

There are several formulas for figuring corn yield, but here's a simple system used by Purdue agronomist Bob 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 feet 5 inches.

Step 2. On every fifth ear, 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-sized kernels.)

Step 4. Yield (bushels per acre) equals (ear number) times (average row number) times (average kernel number) 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-pound 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-foot 5-inch equals 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 bushels.

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

Follow Pamela Smith on Twitter @PamSmithDTN

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