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Soybean stand looks thin; what now?

Soybean Watch: Don’t panic — check the entire field first.

Tom J Bechman 1, Editor, Indiana Prairie Farmer

June 26, 2017

3 Min Read
WHERE ARE THE PLANTS? Spring rains delayed planting, and then the ground crusted. Now you find the thin stand pictured here at one spot. The best advice is to not panic.

You take your hula-hoop out to a late-planted soybean field to do a stand count. You toss it, and it lands like the one shown above. There are seven plants within the hoop. Your heart nearly stops.

You shouldn’t panic right away! There are some steps you can take first that may ease your concern. And by the way, this isn’t the Soybean Watch ’17 field. That field was planted June 6, so expect a report from there next week.

Steve Gauck, sales agronomist for Beck’s, based in Decatur County, will visit the field and help assess the crop. Soybean Watch ’17 is sponsored by Beck’s. Here’s hoping you don’t see another hula-hoop picture with just few plants inside!

Before you panic about a seemingly low stand count, follow these five steps.

1. Fire up your Soybean Field Scout app. The app is for iPhone and Android smartphones. Created by the Purdue University Crop Diagnostic Training and Research Center, it sells for $5.99. Cory Gerber, director of the center, says there is also a Corn Field Scout app for $5.99.

Both are bargains. Besides containing most of the information in the Purdue Corn & Soybean Field Scouting Guide, the apps feature several new calculators.

2. Find the “determining plant populations” calculator. Go to the “hula-hoop method.” The diameter of the hula-hoop in the picture is 26 inches, so plug in 26 inches. Then plug in 7 for number of plants inside the hoop. Hit “evaluate.” The estimated population in the field based on that one spot is 82,743 plants per acre.

3. Check the “information needed for replant decision” chart. According to the guide, in solid seeded rows (the field pictured was drilled in 7-inch rows), if you have 80,000 plants per acre, you can still expect 96% of the full yield potential. Note this is the yield potential for the date the soybeans were planted, not for the date you wanted to plant them.

4. Check the “yield loss by planting date” chart. These soybeans were planted May 20. According to the chart, delay for planting date doesn’t apply. You could still expect 100% of original yield.

However, it drops off quickly from there. If you found this stand on June 10, for example, and decided to tear it up and replant, you would only expect 92% of original yield. If you were hoping for 50 bushels per acre, the new top end, according to this chart, would be about 46 bushels per acre. That’s less than the 48 bushels per acre you could expect from the reduced stand if you had left it.

If you’re just finding this stand now and replant by June 30, averages say expect 70% of original yield. That’s only 35 bushels per acre, if you get a good stand.

5. Remember, the rest of the field may not be this thin, and may be more uniform. The fact is, this was likely the thinnest spot in the field, and perhaps the least uniform. Counts elsewhere were closer to 120,000 plants per acre, much too high to even consider replanting.

The fact that the stand is uneven could come into play in terms of weed issues. Two-foot skips in 50% of the rows can cause a 6% yield loss off the top. It may also affect canopy closure. If the field was drilled May 20, it should have canopied by now. If it’s in 15-inch rows, it may not canopy as fast. Full canopy also helps with weed control.

The bottom line is to assess the entire field and refer to research information before doing something rash like jumping on the tractor to tear up the stand!

About the Author

Tom J Bechman 1

Editor, Indiana Prairie Farmer

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