Thin soybean stands can produce surprisingly high yields

Consider this information when making soybean replant decisions.

Plant stands from 80,000 seeds per acre planting rate. See side-by-side comparison pictures below of 80,000 versus 160,000 seeds per acre panting rate. All photos by Mike Staton, MSU Extension.

Plant stands from 80,000 seeds per acre planting rate. See side-by-side comparison pictures below of 80,000 versus 160,000 seeds per acre panting rate. All photos by Mike Staton, MSU Extension.

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 provided in this article to help inform replant decisions.

The final plant stands and yields of the lowest and the highest planting rates from 32 planting rate trials conducted in Michigan in 2015, 2016 and 2017 are compared in tables 1, 2 and 3 respectively. The planting rate trial results are available in the “SMaRT 2017 On-farm Research Report.” Information provided in the following tables clearly shows that thin soybean stands can produce surprisingly high yields. However, there were exceptions as yields from the 80,000 planting rate were reduced by more than 4 bushels per acre at eight of the 32 sites (25 percent of the time). At three 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 straight-line plant types.

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

LocationRow widthPlanting date Target planting rate (seeds/ac)
80,000 160,000
Stand (plants per acre)Yield (bushels per acre)Stand (plants per acre)Yield (bushels per acre)
Cass 1 15” 13-May 79,100 48.9 133,100 54.5
St. Joseph  Twin 8” 29-Apr 69,800 63.8 138,100 64.7
Tuscola  15” 21-May 54,500 60.1 126,600 59.1
Sanilac 1 30” 21-May 63,200 52.7 138,400 53
Sanilac 2 15” 5-May 71,600 63.2 136,200 57.9
Berrien 30” 22-May 78,500 72.1 150,600 75.9
Cass 2 15” 14-May 78,300 72 150,000 72.4
Monroe 15” 9-May 51,500 38.9 105,800 49.8
Ingham Twin 7” 13-May 79,900 46.5 180,000 47.6
Fairgrove 28” 19-May 73,300 65.8 151,300 66.6
Average 70,000 58.4 141,300 60.2

 

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

LocationRow widthPlanting date Target planting rate (seeds per acre)
 80,000160,000
Stand (plants per acre)Yield (bushels per acre)Stand (plants per acre)Yield (bushels per acre)
Tuscola 1 15” 19-May 66,000 67.2 128,200 71.7
Sanilac 1 22” 21-May 77,100 80.3 149,100 79
Sanilac 2 20” 7-May 59,200 75 124,900 79.3
Tuscola 2 15” 9-May 66,600 78 118,300 80.7
Tuscola 3 15” 9-May 65,000 71.9 122,600 77.7
Sanilac 3 24” 20-May 59,800 61.6 150,900 69.2
Cass 15” 23-May 75,300 75.6 142,300 74.5
Calhoun 30” 16-May 57,300 62 115,800 64.8
Barry 30” 2-Jun 59,000 55 130,000 56.8
Ionia 15” 19-May 69,900 77 128,200 80.1
Ingham Twin 7” 25-May 79,400 53 138,200 51.4
Average 66,800 68.7 131,700 71.4


Table 3. Effect of low soybean planting rates on final plant stand and yield in 2017.

LocationRow widthPlanting dateTarget planting rate (seeds/ac)
80,000 160,000
Stand (plants per acre)Yield (bushels per acre)Stand (plants per acre)Yield (bushels per acre)
Sanilac 1 22” 19-May 71,200 61 123,100 62.2
Sanilac 2 20” 15-May 66,900 69 124,400 67.6
Tuscola 1 15” 23-May 65,000 50.8 117,600 52.5
Sanilac 3 30” 24-May 72,400 54.3 131,800 57.3
Sanilac 4 30” 31-May 73,000 36.8 155,400 42.9
Saginaw 1 15” 7-Jun 50,500 39.5 89,200 41.6
Saginaw 2 15” 7-Jun 44,000 38.9 92,500 42.5
Shiawassee 15” 15-May 61,600 42.5 131,300 45.8
Tuscola 2 15” 15-May 73,900 56.4 132,900 63.6
Calhoun 30” 8-May 59,600 44 109,300 46.4
Berrien 30” 22-May 69,800 64.2 126,500 65.2
Average  64,400 50.7 121,300 53.4

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 the preceding tables 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.

80,000 seeds per acre 160,000 seeds per acre

Plant stands from the 80,000 seeds per acre planting rate (left/top) and the 160,000 seeds per acre planting rate (right/bottom) from the 2017 Sanilac 2 planting rate trial.

Producers should also consider the fact that soybean yields have been shown to decrease by 0.3 to 0.4 of a bushel per acre per day that planting is delayed after the first week of May when making 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 sites in tables 1 and 3).

This article was previously published in the Summer 2018 issue of the Michigan Soybean News.

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