# Save Time—Use a Hula Hoop to Calculate Soybean Population

June 6, 2018 08:34 AM

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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Tom K
Eagan, MN
6/6/2018 01:23 PM

A straight piece of pvc pipe 8.75 ft long works better. Lay it between two rows and count the plants on each side then multiply by 1000 for 30 inch rows. A hoop on 30 in rows will get you high variability depending on diameter of the hoop and where it lands when you throw it. In drill beans a hoop works good. Different row spacing require different methods for counting stands.

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