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Estimating soy yield inexact, but here is how to get close
By CELESTE BAUMGARTNER
Ohio Correspondent

COLUMBUS, Ohio — Estimating soybean yields is a tricky business. Grain farmer Tim Hesselbrock checked to see how his pods were filling out to estimate yields, but there were many variables.

“We look to see how many beans are in the pods,” he said. “As for trying to guess yields, that’s a hard thing to do because moisture makes a big difference. We need a lot of rain in August and September to make good pod fill.”

Ohio State University soybean expert Laura Lindsey said there are four components farmers can look at to estimate yields, but agreed it is an inexact science. She also said yield is determined later in the season, depending on rainfall and other variables. Estimating yields gets more accurate as the growing season progresses.
The four estimating components are: number of plants per acre; number of pods per plant; number of seeds per pod; and amount of seeds per pound, or the seed size. “For the number of plants per acre, we usually recommend counting how many plants there are in 1/1000th of an acre,” she said. “If you are in 7.5-inch row spacing, count the number of plants in 69 feet, 8 inches of row.”

In a 15-inch row spacing, count 34 feet, 10 inches of row. In 30-inch rows, count the number of plants in 17 feet, 5 inches of row.
To estimate the number of pods per plant, Lindsey recommends collecting at least 10 plants at random. The more plants collected, the more accurate the count will be. The important thing is to randomly select plants. “Sometimes we have a tendency to pick the nice-looking plants, which won’t necessarily give you the best results,” she said. “Pull those plants and count the number of pods. Take an average number of pods per plant.

“You can then open the pods and look at how many seeds there are per pod. If you don’t want to do this you can use 2.5 as an estimate, but it is more accurate if you actually count the number of seeds per pod. Do this on the 10 plants you collected randomly and take an average.”

The last thing the grower does is estimate the number of seeds per pound. This requires a scale. The estimator can count out 100 seeds and weigh them, then convert that to how many seeds it takes to make a pound.

It’s not as accurate, but farmers can estimate 3,000 seeds per pound. In a stressful year it will take more seeds to make a pound. In a good year, the seeds may be larger, so it will take fewer seeds to make a pound.

To find the number of bushels to the acre, multiply the number of plants in 1/1000th of an acre times the number of pods on a plant, times the number of seeds in a pod. Divide that by the number of seeds in a pound, multiplied by 0.06.

Results are more accurate if it is later in the growing season and if this calculation is done in several areas of the field.
8/22/2013