Thin soybean stands can produce surprisingly high yields

Consider this information when making soybean replant decisions.

Soybean emergence and final plant stands can be reduced by a number of factors, including:

  • Rainfall occurring within 24 hours after planting
  • Soil crusting
  • Insects
  • Diseases
  • Poor seed-to-soil contact
  • Planting too deep or too shallow

When poor soybean emergence and thin stands occur, producers are compelled to make timely and informed replant decisions. Accurately assessing your soybean stand and diagnosing the cause of the emergence problems are the first steps in the process. Once the existing stand has been determined, use the information in Tables 1 and 2 to help inform replant decisions.

The plant stands and yields of the lowest and the highest planting rates from 21 planting rate trials conducted in Michigan in 2015 and 2016 are compared in Tables 1 and 2, respectively. The planting rate trial results are available in the “SMaRT 2016 On-farm Research Report.”

Information provided in Tables 1 and 2 clearly shows that thin soybean stands can produce surprisingly high yields. There were exceptions to this as yields from the 80,000 planting rate were reduced by more than 4 bushels per acre at six of the 21 sites (29 percent of the time). At two of these sites, the yield loss was more than 7 bushels per acre. It should be noted that none of the varieties planted in the trials were thin or narrow plant types.

Soybean agronomists have identified 100,000 plants per acre in narrow rows and 80,000 plants per acre in 28- and 30-inch rows as the minimum plant stands required to produce optimum yields. However, the information presented in Tables 1 and 2 shows that fields having plant stands of less than 80,000 plants per acre have the potential to produce high yields.

I urge producers to consider this information when making soybean replant decisions. The case for keeping reduced stands becomes even stronger for fields having a history of white mold. The lower plant stands may actually produce higher yields than higher plant stands when conditions favoring the development of white mold occur (see the Sanilac 2 site in Table 1).

Table 1. Effect of low soybean planting rates on final plant stand and yield in 2015

Location

Row spacing (inches)

Target planting rate (seeds/acre)

80,000

160,000

Stand (plants/acre)

Yield (bushel/acre)

Stand (plants/acre)

Yield (bushel/acre)

Cass 1

15

79,100

48.9

133,100

54.5

St. Joseph

Twin 8

69,800

63.8

138,100

64.7

Tuscola

15

54,500

60.1

126,600

59.1

Sanilac 1

30

63,200

52.7

138,400

53.0

Sanilac 2

15

71,600

63.2

136,200

57.9

Berrien

30

78,500

72.1

150,600

75.9

Cass 2

15

78,300

72.0

150,000

72.4

Monroe

15

51,500

38.9

105,800

49.8

Ingham

Twin 7

79,900

46.5

180,000

47.6

Fairgrove

28

73,300

65.8

151,300

66.6

Average

70,000

58.4

139,700

60.2

 

Table 2. Effect of low soybean planting rates on final plant stand and yield in 2016

Location

Row spacing (inches)

Target planting rate (seeds/acre)

80,000

160,000

Stand (plants/acre)

Yield (bushel/acre)

Stand (plants/ac)

Yield (bushel/acre)

Tuscola 1

15

66,000

67.2

128,200

71.7

Sanilac 1

22

77,100

80.3

149,100

79.0

Sanilac 2

20

59,200

75.0

124,900

79.3

Tuscola 2

15

66,600

78.0

118,300

80.7

Tuscola 3

15

65,000

71.9

122,600

77.7

Sanilac 3

24

59,800

61.6

150,900

69.2

Cass

15

75,300

75.6

142,300

74.5

Calhoun

30

57,300

62.0

115,800

64.8

Barry

30

59,000

55.0

130,000

56.8

Ionia

15

69,900

77.0

128,200

80.1

Ingham

Twin 7

79,400

53.0

138,200

51.4

Average

66,800

68.7

131,700

71.4

This article was produced by the SMaRT project (Soybean Management and Research Technology). The SMaRT project was developed to help Michigan producers increase soybean yields and farm profitability. The SMaRT project is a partnership between Michigan State University Extension and the Michigan Soybean Checkoff program.

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