Source: Bob Battel, Michigan State University Extension Field Crops Educator
Michigan State University Extension educators in the Thumb and Saginaw Valley studied optimal soybean seed populations in multiple on-farm population studies in 2009 and 2010. Planted populations ranged from 80,000 to 240,000 seeds per acre with incremental increases of 40,000 seeds. Harvested populations were generally similar to planted populations. The soybeans were planted in 30-inch rows, and the variety Pioneer 92Y30 was used both years. These results represent 15 study replications over the two years. It should be noted that these studies were established on high yielding, well-tiled loams and clay loams throughout the tri-county Thumb region.
Gross per acre returns for each population were calculated using a soybean price of $12.90 per bushel and a cost of $45 for a 140,000 seed unit. Thus, each incremental increase of 40,000 seeds increases costs $12.86 per acre, and an additional 1 bushel per acre yield would be necessary to cover the increased seed cost. See the following table for results.
Soybean Population Per Acre Returns
Seed at $45/Bag and Soys at $12.90/Bu.
Pop X 1,000
2009 Yield (bu./A)
2010 Yield (bu./A)
2 Year Ave Yield (bu./A)
Results between 2009 and 2010 were substantially different. In 2009, the 200,000 and 240,000 populations were significantly greater than lesser populations at the 0.05 level. In 2010, each population between 120,000 and 240,000 were statistically similar, and significantly greater than the 80,000 population. When averaged together, and with the seed costs factored in, it is clear that more profitable yields are realized at populations greater than 80,000 seeds per acre by about $30 per acre. But within the 120,000 to 240,000 seed range, the results are not different enough to recommend one population over another at this point. This study will be repeated in 2011 to help clarify differences in yield between soybean populations.
The Michigan Soybean Promotion Committee provided funding to make this study possible.