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Get out the Hula-Hoop to Check Soybean Stands

Soybean field
Some quick math will tell you what type of stand you have.

Those soybeans planted in mid-April should be coming up soon, if they're not already. Hopefully, you've got a good stand. If you're not sure, knowing you still have plenty of time to replant, how can you tell just how many plants you actually have per acre without just guessing?

One of the easiest methods is referred to as the 'hula-hoop' method, because you can do it using a child's hula-hoop. Or you can fashion a hoop out of stiff wire and use it instead. It's a handy diagnostic tool to help you quickly determine what your actual stand is in terms of plants per acre. The secret is sampling enough spots within the field to get an accurate picture of what's happening there.

Here's an example. You can follow along in the Purdue University Corn & Soybean Field Guide, 2010 edition, pages 108 and 109. To learn how to get a guide if you don't have one, contact:

Suppose your hoop has a diameter of 30 inches. Then you need to tuck away an important number you will use as a correction factor. For 30 inches, the factor is 8,878. Factors for hoops of 18, 21, 24, 27, 33 and 36 inches respectively, are 24,662, 18,119, 13,872, 10,961, 7,337 and 6,165.

Take your hoop to the field and select at least five areas within the field at random. Count the number of plants inside the hoop each time after you roll or throw the hoop at random.

Now average your counts together. Suppose you count an average of 18 plants inside the ring in five tosses. Then to find total population per acre, you simply multiply the average number of plants by the multiplication factor. In this case, it becomes: 18 plants times 8,878. That equals 159, 804 plants per acre.

Count that as an excellent stand, assuming it's uniform through the field. Many people today are only planting 160,000 to 170,000 seeds per acre in 15-inch rows.

Remember, if you use a different sized-hoop, then the number you multiply by will change.

The great thing about using a hula-hoop or wire circle is that you can use it over and over. You don't have to destroy any plants. Simply roll or throw it, then count plants on the inside of the circle.


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