Michigan’s Thumb area study confirms MSU recommendation for soybean populations

MSU Extension educators studied the effects of soybean planting populations in 30-inch rows over a three-year period under growing conditions in Michigan’s Thumb.

MSU Extension educators in the Thumb and Saginaw Valley studied the effects of optimal soybean seed populations in multiple on-farm studies conducted in 2009, 2010 and 2011. Planted populations ranged from a low of 80,000 seeds per acre to 240,000 seeds per acre in increments of 40,000 seeds. See Table 1 for harvest populations in 2011.

Table 1. Planted versus actual population

Planted Population (X1000) Actual Population (X1000) % of Intended Population
80 72 91
120 117.6 98
160 132.8 83
200 180 90
240 216 90

Plots were established in a Randomized Complete Block design with four replications. Plots were 100 feet long by 15 feet wide. Each of the three years, the studies were replicated at three sites. Thus, the following data represents 18 study replications over the three years. During the first two years of the study, the variety used was Pioneer 92Y30. In 2011, NK S19-A6 was used at one site and Pioneer 92Y51 was used at the other two sites.

Gross returns per acre for each population were calculated using a soybean price of $11.65 per bushel and a cost of $45 for a 140,000 seed unit. Each incremental increase of 40,000 seeds increases costs to $12.86 per acre, and an additional 1.1 bushel increase in yield would be necessary to cover the increased seed cost. See Table 2 for results over the three years the study was conducted.

Table 2. Soybean population per acre returns - seed at $45/bag and soys at $11.65/bushel

Pop X 1,000 2009 Yield (bu./A) 2010 Yield (bu./A) 2011 Yield (bu./A) 3 Year Ave Yield (bu./A) Return/A
80 36.8 44.0 50.4 43.7 $483.74
120 43.2 44.5 52.3 46.7 $505.17
160 43.9 45.8 52.1 47.3 $499.38
200 44.8 44.8 52.8 47.5 $488.66
240 48.8 45.0 50.9 48.2 $484.58

Findings over three years confirm the MSU recommendation of planting soybeans at 130,000 seeds per acre in 30-inch rows.

This project was made possible with funding from the Michigan Soybean Promotion Committee.

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