By Michael Staton
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 39 planting rate trials conducted in Michigan in 2015, 2016, 2017 and 2018 are compared in Tables 1, 2, 3 and 4, respectively. The detailed information from all the planting rate trials conducted from 2015 to 2018 is available in the 2017 and 2018
SmaRT On-farm Research Reports. 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 nine of the 39 sites (23 percent of the time). Four bushels per acre is the breakeven yield loss for the 80,000 planting rate given current seed and crop prices. 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. |
|---|
| Location | Row width | Planting 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. |
|---|
| Location | Row width | Planting date | Target planting rate (seeds per acre) |
|---|
| 80,000 | 160,000 |
|---|
| 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. |
|---|
| Location | Row width | Planting 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) |
|---|
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 | 41.9 | 89,200 | 42.2 |
Saginaw 2 | 15” | 7-Jun | 44,000 | 43.0 | 92,500 | 47.2 |
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 | 51.3 | 121,300 | 53.8 |
Table 4. Effect of low soybean planting rates on final plant stand and yield in 2018 |
|---|
|
Location |
Row width |
Planting date | Target planting rate (seeds per acre) |
|---|
80,000 | 160,000 |
|---|
Stand (plants per acre) | Yield (bushels per acre) | Stand (plants per acre) | Yield (bushels per acre) |
|---|
Tuscola | 15” | May 14 | 64,700 | 66.0 b | 124,200 | 68.5 |
Sanilac 1 | 30” | May 18 | 74,700 | 59.5 | 130,200 | 63.5 |
Barry 1 | 30” | May 8 | 62,800 | 65.3 | 97,900 | 62.5 |
Sanilac 2 | 22” | May 25 | 54,500 | 79.2 | 121,000 | 81.4 |
Barry 2 | 30” | May 8 | 51,500 | 53.9 | 92,300 | 57.7 |
Saginaw | 30” | June 7 | 57,400 | 66.2 a | 105,100 | 61.2 |
Eaton | 15” | June 14 | 66,900 | 57.9 b | 122,800 | 60.7 |
Average | | | 61,800 | 64.0 | 113,400 | 65.1 |
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. 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.
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.
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 and the Saginaw site in Table 4). The lowest planting rate increased soybean yields by 5 bushels per acre and income by $80 per acre over the highest planting rate at these locations.