Maximizing returns on soybean seed investments – 2013 trial results

With more expensive soybean seed, farmers may question just how low a population they can plant to remain profitable. Studies in Michigan’s Thumb help answer that question.

Michigan State University Extension educators who work with the Thumb Ag Research and Education (TARE) project evaluated five soybean seeding populations in 2013. Planted populations ranged from 100,000 seeds per acre to 210,000 seeds per acre in increments of 30,000 seeds. This population study was established at two sites at Elkton, Mich., and Fairgrove, Mich. This study was similar to a series of studies established 2008-2012 by the TARE group when the evaluated populations ranged from 80,000 to 240,000 in increments of 40,000 seeds.

Soybeans were planted in 30-inch rows and the variety used was Rupp 7251 treated with Cruiser, fungicide and an inoculant. Note that the studies were established on high-yielding, well-tiled, loamy ground. Actual plant stands were measured in August. The Fairgrove site was planted on June 3, 2013, and the Elkton site was planted on June 5. Actual populations were about 83 percent and 80 percent of planted populations at the Elkton and Fairgrove sites, respectively. Actual populations more closely matched planted populations at the lower ranges (100,000 and 130,000) at both sites. See the following table for more information.

Planted Pop X 1,000

Elkton

Fairgrove

Average

Final Pop X 1,000

% of planted

Final Pop X 1,000

% of planted

Final Pop X 1,000

% of planted

100

85.9

86%

87.1

87%

86.5

87%

130

111.6

86%

106.4

82%

109.0

84%

160

129.3

81%

127.9

80%

128.6

80%

190

151.5

80%

146.4

77%

149.0

78%

210

173.9

83%

153.5

73%

163.7

78%

See the following table for soybean yield at the varying populations.

Two site average yield by population

Planted Pop X 1,000

Final Pop X 1,000

Yield (Bu/A)

100

86.5

49.6

130

109.0

52.6

160

128.6

53.0

190

149.0

50.8

210

163.7

51.0

All planted populations of 130,000 seeds per acre and greater (stands of 109,000 plants per acre and greater) yielded greater than 50 bushels per acre. The 100,000 seeding rate (86,500 plants per acre) yielded less than 50 bushels per acre.

The following table shows a regression analysis of the data from the two sites. Values of $13 per bushel for soybeans and $63.50 per 140,000 seeds were used for the regression analysis.

Regression analysis of two sites

According to the regression analysis, maximum yield was realized at 129,000 plants per acre and maximum return was realized at 119,000 plants per acre, or 147,000 seeds per acre at 81 percent average stand.

This study will be repeated in 2014 and 2015.

The author gratefully acknowledges the assistance of Bob Nielsen, Professor of Agronomy, Purdue University, for providing the regression analysis, and for his assistance in interpreting these results.

The Michigan Soybean Promotion Committee provided funding to make this study possible. 

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