Soybean School: Counting plants to assess stand establishment

Soybeans have been slow to emerge and establish across Ontario this spring as cooler weather has tempered the vigour of the heat-loving crop.

Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) soybean specialist Horst Bohner notes that the crop tends to flourish early in the season when the daytime temperature reaches 28 degrees C and nights hover around 24 degrees C. Overall, most soybean fields across the province are at the 2nd and 3rd trifoliate stage as the calendar pushes into mid June.

Bohner is encouraging all growers to scout their fields to determine how their plant stands stack up and assess yield potential. On this episode of RealAgriculture’s Soybean school, he looks at two methods growers can use to determine plant populations and assess their stands. He quickly reviews the traditional hula hoop method which requires a grower to count the number of plants in the hoop on average when it’s tossed randomly across the field. If the hoop averages 12 plants, for example, the population is estimated at 75,000 plants.

When it comes to the recommended plant numbers, Bohner notes that 90,000 plants per acre are required on lighter textured soils and loam soils. That number increases to 110,00 plants on heavier clay-type soils. “If you are below that you really have to start thinking about whether you have to beef that population up with a replant or another pass,” he adds.

Bohner also shares a simple plant counting method based on the number of square feet in an acre — 43,560. “Basically, one plant per square foot is not enough; two plants per square foot is okay (no replant is required); and three plants per square foot is a normal stand,” he adds. In the video, he demonstrates how growers can do a simple calculation using their own feet as they walk through soybean fields. “2.5 plants per foot is equal to about 100,000 plants per acre…. If I average four plants per foot length, it’s about 140,000.”

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