Soybean Seeding Rate and Row Width Effect on Yield

Soybean seed costs have increased over the past few years, driven in part by soybean seed being priced similar to corn seed.  That is, farmers are now buying soybeans by the seed, a departure from buying soybeans by the pound.  As a result, there is great interest from farmers in reducing soybean seeding rates and maintaining maximum yield.  I’ve seen several farmers in the Van Wert area move away from using a drill to sow soybeans.  The trend has been towards planting soybeans in 15″ rows with a planter unit.

For years, we’ve been researching soybean seeding rate and row width effect on soybean yield. Multiple years of research at Farm Focus has shown 15 inch row planting width comparable in yield to 7.5 inch row planting width. In good growing conditions, OSU research indicates the the most profitable seeding rate is about 150,000 seeds per acre, which results in a harvest population of slightly more than 100,000 plants per acre.  In the poor growth environment, the most profitable seeding rate was just over 200,000 seeds per acre and resulted in a harvest population of about 180,000 plants per acre.

As long as soybeans are maintained at 15 inch row width, sunlight energy capture is maximized, which drives photosynthesis.  Ultimately, it is photosynthesis efficiency during the critical reproductive stage that helps determine soybean yield.   As a general rule for our area, final populations of 100,000 to 120,000 plants per acre are adequate for maximum yield for soybeans planted prior to May 20.

Lets take a closer look at some recent research.  In 2008, we evaluated two different soybean planting widths, 7.5″ and 15″, consisting of three different seeding rates: 100,000, 150,000, and 200,000 seeds per acre.  Results from this soybean study showed that 15 inch row planting width was  comparable in yield to 7.5 inch row planting width. That is, the 15 inch row spacing at 100,000 seeds/A was not statistically different than the 7.5 inch row spacing at 100,000 seeds/A, and so forth.

In 2006 we researched four different soybean row widths at specified planting populations. The widths were as follows: 7.5″, 15″, twin-row, and 30″.  Yields were not statistically different for the 7.5-inch, 15-inch, and twin row spacing row widths. The 30-inch row soybean spacing treatment was statistically lowest among the row width treatments.

2008 full study- http://farmfocus.osu.edu/beans_population_row_width-08.pdf

2006 full study- http://farmfocus.osu.edu/bean_row_width-06.pdf

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