Many soybean producers in South Dakota have embraced the practice of early soybean planting in recent years. At a workshop this winter, one producer in northern South Dakota mentioned his intention to begin planting soybeans as early as April 15th. This would be considered ‘ultra-early’ soybean planting, and it seems to be increasing in popularity. Some producers feel they have ‘nothing to lose’ when planting ultra-early, as most seed companies will provide full or partial seed replacement in replant situations, regardless of the reason.
University on-farm research has shown no consistent yield benefits to ultra-early planting when compared to the last week of April or the first week of May. The main benefit of planting ultra-early is to extend the planting window… or to try and ensure the last soybean field planted still has the same yield potential as the first. While planting this early offers some benefits, it also carries some risks, which will be outlined in this article.
Risks to Consider
Frost or Freeze Damage
A major risk of planting early is plant damage or death from freezing temperatures (Figure 1). Several major soybean growing areas in South Dakota can see an average last frost date as late as May 7-9. The growing point of a soybean is vulnerable once the cotyledons have emerged. Soybean cotyledons are more-resistant to freezing than corn; air temperatures need to be below about 30°F for damage to occur. Once the trifoliate leaves emerge, temperatures below 32°F may cause damage. High-residue environments may help protect the seedlings from cold temperatures; however, high residue may inhibit soil warm-up.
Imbibitional Chilling Injury
When soybeans imbibe cold water (<45°F) within 24 hours of planting, injury can occur. Visible symptoms include poor, uneven emergence and dead tissue on the exterior of the cotyledons. This type of injury often happens when a cold front bringing rain and cold temperatures occurs immediately following planting. Cold injury can occur after 24 hours, but the symptoms are usually less severe. To mitigate the potential for chilling injury in cool soil temperatures:
- Plant high-quality seed with good early-season vigor.
- Avoid planting seed that is excessively dry. Dry seed imbibes more moisture.
- Avoid planting if rain chances are high within 24 hours of planting.
- Begin planting in the early afternoon to allow soils to warm up.
Disease pressure is greater due to the probability that early-planted soybeans will encounter cool and wet soils. Choose varieties that are resistant to Sudden Death Syndrome and phytophthora. In addition, fungicide seed treatments are always recommended for early-planted soybeans. Choose seed treatments that are effective against fusarium, pythium, phyphophthora and rhizoctonia. Some company promotion materials have suggested that seed treatments are all that is needed to protect ultra-early planted soybeans, but this is an exaggeration. The consensus among extension specialists is that seed treatments are one tool that can help to keep soybeans healthy in early planting situations.
Bean Leaf Beetles
Some areas of the South Dakota may have issues with bean leaf beetles on early-emerging soybeans, as there are not many alternative food sources early in the growing season. Insecticide seed treatments and foliar applied insecticides may help in situations of high infestation.
Reduced Plant Populations
Any of the problems listed previously may cause a reduction in final stands. It’s important to remember that a stand of 100,000 plants per acre is enough for maximum yield potential. University research has shown no consistent benefit to increasing planting populations in early-planted soybeans.
No matter the calendar date, it is not recommended to plant soybeans when soil temperatures are less than 40°F. Ultra-early planting of soybeans has not shown consistent yield benefits. Planting date studies in the northern states (South Dakota, Minnesota, Wisconsin, and Michigan) have shown that potential yield loss in soybeans typically begins to occur when planting occurs after April 25th, with an average loss of about 0.3 bu/acre per day. However, potential yield loss is minimal in the early-season timeframe. Beginning May 10th, yield potential begins to decline more rapidly, at about 0.5 bu/acre per day.
When planting early, consider using a longer relative maturity variety. For example, research indicates that a 1.6 to 1.8 RM soybean is the ideal maturity for east-central South Dakota when planting occurs in mid-May. When planting in late April, it seems that a 2.1 to 2.3 RM will have a yield advantage in most growing seasons.
Early soybean planting offers potential yield benefits, but also poses some risks. When planning for early or ultra-early soybean planting, consider the suggestions in this article when making management decisions.
- Conley, S. “Just the Facts Jack: Soybean Planting Date, Seeding Rate and Seed Treatment Recommendations.” Web blog post. Cool Bean Blog. 4/11/2022. Web. Accessed: 4/20/2022.
- Licht, M. “Mitigating the Risks of Very Early Soybean Planting.” Web blog post. Iowa State University Extension and Outreach – Integrated Crop Management. 4/12/2020. Web. Accessed: 4/20/2022.
- Staton, M. and H. Bohner. 2020. Identifying and mitigating the risks of ultra-early soybean planting. Soybean News – Michigan State University Extension. East Lansing, MI.