By Michael Staton
When poor soybean emergence and thin stands occur, producers need 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, the following information may help producers make an informed replant decision.
Sixty-six planting rate trials conducted in Michigan from 2015 to 2021 are summarized in Table 1. The average final plant stands and average yields for the lowest and the highest planting rates are shown. There were 10 locations in 2015, 10 sites in 2016, 11 sites in 2017, eight sites in 2018, nine sites in 2019, nine sites in 2020, and eight sites in 2021. Detailed information from all the planting rate trials conducted from 2015 to 2021 is available in the 2017 to 2021 On-farm Research Reports available at the Michigan Soybean Committee website.
The data shows that thin soybean stands can produce surprisingly high yields. However, there were exceptions as yields from the 80,000 seeds per acre planting rate were reduced by more than 2.5 bushels per acre at 23 of the 66 sites (32% of the time). This is the approximate breakeven yield loss for the 80,000 planting rate given current seed and crop prices ($60/140,000 seeds and $14.40/bushel) making the 80,000 rate less profitable than the 160,000 rate at these sites. At four of the sites, the yield loss in the lowest planting rate was more than 7 bushels per acre. None of the varieties in the trials were thin or straight-line plant types.
Table 1. Average final plant stands and yields by year for the lowest and highest planting rates compared in 66 on-farm planting rate trials conducted in Michigan from 2015 to 2021. |
|---|
Year | Target planting rates (seeds per acre) |
|---|
80,000 | 160,000 |
Stand (plants per acre) | Yield (bushels per acre) | Stand (plants per acre) | Yield (bushels per acre) |
2015 | 70,000 | 58.4 | 141,300 | 60.2 |
2016 | 66,800 | 68.7 | 131,700 | 71.4 |
2017 | 64,400 | 51.3 | 121,300 | 53.9 |
2018 | 61,800 | 64.0 | 113,400 | 65.1 |
2019 | 64,300 | 58.1 | 120,000 | 62.0 |
2020 | 63,100 | 56.2 | 1117,500 | 60.1 |
| 2021 | 64,400 | 64.2 | 124,700 | 67.8 |
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 Table 1 shows that stands of 60,000 to 70,000 plants per acre can produce high yields. Also, realize that soybean yields decrease by 0.3 to 0.4 of a bushel per acre per day when planting after the first week of May. I urge producers to consider this information, the information presented in Table 1, and to refer to an excellent publication from the University of Wisconsin, “Think Twice Before Replanting Soybeans,” when making replant decisions.
The case for keeping thin stands becomes even stronger for fields having a history of white mold. The lowest planting rate increased soybean yields by 5 bushels per acre and income by $100 per acre (using current seed and market prices) over the highest planting rate at two sites infested with white mold.
This article was produced by a partnership between Michigan State University Extension and the Michigan Soybean Committee.
Source : msu.edu