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Factor in less-than-ideal spots when estimating corn yield

Tom J. Bechman hand holding 2 ears of corn, shucked
SELECT RANDOM EARS: Make sure you select the ears that will represent row number and kernel count in your yield estimate at random.
Corn Watch: Areas hurt by too much water or nitrogen loss will bring down average yield.

It’s time to estimate corn yields. The secret to accurate yield estimates is picking spots at random and selecting ears to examine at random, Dave Nanda says. He is director of genetics for Seed Genetics Direct, the company that sponsors Corn Watch ’21.

“If you pick bigger ears, even subconsciously, you aren’t going to get an accurate picture of what you will likely harvest,” Nanda says. “Remove the bias if you can.”

Related: Stay alert to multiple symptoms in fields

The Purdue University Corn & Soybean Field Guide explains the basic formula. Lay off 17 feet, 5 inches using a rope marked to that length or a tape measure. That represents 1/1,000 acre in 30-inch rows. Count ears to get total ear count. Nanda prefers counting on either side of the row or tape, and then averaging to get the final ear count there. Stalks with very small ears should not be counted.

Then count number of rows per ear and kernels per row on three to five ears and average them together. Multiply number of ears per 1/1,000 acre by number of kernel rows by number of kernels per row, and divide by a factor representing total number of kernels per bushel, giving yield per acre. Many people use 80 as the factor. If kernels are shallow or lighter, use 85 or 90. If they’re very large, use 75.

Uneven fields

The Corn Watch ’21 field presents a challenge in estimating average yield. It contains different soil types, and the lighter, somewhat poorly drained soils lost more nitrogen, even though N was applied in April with stabilizer. Obvious signs of nitrogen deficiency appeared by pollination, mainly on those soils. Some nitrogen was added when a fungicide was applied, but a drone flight in early August confirmed some areas were lighter in color, indicating plants were likely short on N.

Here’s an example using information gathered from field counts and the aerial map.

1. On 50% of the field with fewer nitrogen issues due to soil type, 90% of it looks this way: (good corn on better half of field) 30 ears times 17 rows times 40 kernels divided by 80 equals 255 bushels per acre.

2. About 10% of the corn on the better half of the field looks this way: (lighter-colored corn on better half) 28 ears times 16 rows times 34 kernels divided by 85 equals 179.2 bushels per acre.

Combining the two estimates, that half of the field pencils out at 247.5 bushels per acre.

3. On the second half of the field with more low nitrogen spots, 60% of the corn is as good as the best corn on the other half of the field, estimated at 255 bushels per acre.

4. For the other 40%, here is an example based on stand counts in the poorer areas: 26 ears times 16 rows times 30.5 kernels divided by 90 equals 140 bushels per acre.

Combining the two, based on percentages of each type, yield estimate is 209 bushels per acre for that half of the field.

Harvest 247.5 bushels per acre on half the field and 209 bushels per acre on the other half, and the field average estimate is just over 228 bushels per acre.

Call it 225 bushels per acre for the Corn Watch ’21 field. Time will tell if that’s in the ballpark.

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