Save Time—Use a Hula Hoop to Calculate Soybean Population

Kyle Allen calculates soybean populations with the hula hoop method near Hawk Point, MO (2017). ( Sonja Begemann )

Farmers across the U.S. are out scouting, and in some cases spotty soybean fields are leaving them wondering if there are enough plants out there to grow a crop. Cutworms, weather, whatever, scout to determine what’s going on—and save time by calculating soybean populations with a hula hoop.

Replant is a tricky decision and will depend on a farmer’s end yield goal. If a stand looks spotty, check to see what population is left and what that means for yield at the end of the season. Be sure to check several areas of the field, at least five, to find a field average.

Upon entry, throw the hula hoop into the field. This ensures the location is picked at random, and when done at least five times should show an adequate representation of what’s in the field. Count how many plants are in the hoop then multiply that by the hula hoop “factor” to determine average plants per acre. The factor represents how many hoops fit in one acre and can be found in field guides, such as Purdue’s.

Purdue provides factor information for various hula hoop diameters:

Diameter of Hoop

Factor

18”

24,662

21”

18,119

24”

13,872

27”

10,961

30”

8,878

33”

7,337

36”

6,165

 

For example, a 24” hula hoop with 13 plants means 13 x 13,872 and an average population of 180,336. Some field guides will also provide tables with the math already completed for these and additional hula hoop sizes.

See the hula hoop method step-by-step in this video taken last year in Hawk Point, Mo.

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