Hula hoops?

Hula hoops provide an additional technique for calculating soybean populations.

Photo by Sonja Begemann

While you might think of hula hoops as a game for children they’ve found a new use—helping farmers calculate soybean populations. With no need for a tape measure, this method could save time and help farmers make critical decisions such as replant.

“We’ve had about 30% replant in corn this year and are looking at about 5% replant so far in soybeans,” says Kyle Allen, Channel seedsman near Hawk Point, Mo. “Rain has caused crusting or washed away seeds, especially in no-till.”

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.