February 1, 2023
Soybean planting date has become a hot topic in many soybean producing regions across the United States. Particularly when looking at the early planting time frames of late March and April, and the recommendation to plant soybean before corn, which is a new concept in the northern growing areas of Minnesota, Wisconsin, Michigan, and the Dakota’s. High yielding genetics, improved seedling disease tolerance, enhanced fungicide seed treatments, and better planting techniques have contributed to the ability to plant earlier, faster, or increase the breadth of the planting window without a typical yield penalty.
It is commonly understood that soybean is more tolerant or adaptive to planting date compared to corn, with a recommended planting date window running from late March to mid-May without much yield differences or penalties, particularly when compared to corn (Figure 1). Yet, much of the new research has shown when soybean planting moves into May, yield potential begins to decline after May 1 and the rate of decline increases after May 15 (Table 1). A study in Wisconsin looking at farmer data indicated a 0.4 to 0.5 bu per acre per day yield loss when planting was delayed past April 25.1
Figure 1. Relative performance of corn and soybeans at different planting dates combined over years in 2020 and 2021.(1)
| Planting Date | Yield Loss (%) | Yield Potential (% of maximum) |
|---|---|---|
| May 1 | 0 | 100 |
| May 5 | 1 | 99 |
| May 10 | 2 | 98 |
| May 15 | 3 | 97 |
| May 20 | 6 | 94 |
| May 25 | 9 | 91 |
| May 30 | 13 | 87 |
| June 4 | 18 | 82 |
| June 9 | 24 | 76 |
| June 14 | 30 | 70 |
*Naeve, S. L. and Nicolai, D. 2018. When and how to plant soybean. University of Minnesota Extension. Permission for use granted by Dr. Naeve, University of Minnesota.
One reason early planting can be advantageous is that soybean plants are able to harvest more sunlight with an earlier and potentially larger canopy. Because soybean plants are photoperiod sensitive, earlier planting generally means the plants spend more time in the vegetative phase which ultimately equates to more nodes where potential pods set and seeds fill. Additionally, the greater sunlight capture results from an earlier canopy closure. This means more overall light interception, and an increased surface area for photosynthesis when reaching critical stages of pod set and seed fill. A side benefit from the earlier canopy closer and denser canopy is reduced weed populations and competition.
To answer the question “when is the optimum time to plant soybean”? It often comes down to, “it depends”, particularly on geography, rainfall patterns, and spring frost free dates. Yet in general, most recent research has shown early (for the area) planted soybean crops typically have a greater opportunity for upside yield potential with an increased opportunity to capture light energy and add more pod bearing nodes (Figure 2). Ultimately the “best” planting dates is the earliest opportunity when soil conditions and forecasted weather patterns align to allow for a good seedbed and emergence environment that create uniform emergence and healthy seedlings.
Figure 2. Minnesota soybean field planted April 27, 2022.
Sources
1Corn and soybean planting timing decisions. 2021. Bayer Research (2020 and 2021). Illinois. https://www.channel.com/en-us/agronomy/corn-and-soybean-planting-timing-decisions.html.
2Naeve, S. L. and Nicolai, D. 2018. When and how to plant soybean. University of Minnesota Extension. https://extension.umn.edu/soybean-planting/when-and-how-plant-soybean#when-to-switch-maturities-522061/.
3Rattalino Edreira, J.I., Mourtzinis, S., Conley, S.P., Roth, A.C., Ciampitti, I.A., Licht, M.A., Kandel, H., Kyveryga, P.M., Lindsey, L.E., Mueller, D.S., Naeve, S.L., Nafziger, E., Specht, J.E., Stanley, J., Staton, M.J., and Grassini, P. 2017. Assessing causes of yield gaps in agricultural areas with diversity in climate and soils. Agricultural and Forest Meteorology. 247 (2017) 170-180.
Web sources verified 12/13/22
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