By Michael Staton
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.