Soybean planting date. Plant early. What’s early? February? March? Before corn? Simultaneously with corn? These questions and many, many more come up in discussion whenever this topic is broached. And it comes up often these days. Over the past few seasons, agronomists have been recommending that growers move soybean planting dates earlier to get higher yields. Growers have responded by adopting earlier planting in greater numbers than many of us who made these recommendations expected.

My first comment is that the term “early” is very subjective and relative. Everyone gets a picture in their head when the term early is used. In my way of thinking and in this part of the world, early planted beans are any in the ground before April 30. In some years early beans may not be planted until May 15 due to soil and weather conditions. Early is more a way of thinking than any hard and fast rule.

Most often, the goal of planting soybeans early is to provide for increased vegetative growth prior to R1, first flower. This stage has historically been assumed to start on June 21, the summer solstice. Dr. Shawn Conley, soybean extension specialist with the University of Wisconsin, points out that longer nights before the solstice may induce flowering earlier in soybeans planted earlier. This combination of more vegetative growth (more nodes) and more light interception, plus a longer flowering period, can produce more flowers and can increase yield potential.

Along with early planting, another management practice to help increase yield potential is to use the latest possible Maturity Group (MG). Research suggests that this will, in most seasons, maximize soybean yields under all but the latest of planting dates, where planting has been delayed past mid-June.

Conley’s research also indicates that Illinois growers are already planting within the optimal dates for their geography. In Identifying Optimal Soybean Planting Dates Across the U.S., he states that, “It is evident that many progressive farmers in the North Central U.S. region (e.g., Illinois), continuously monitor and strive to plant crops earlier on an annual basis.” Read that again. “Continuously monitor.” That’s what has been going on, that’s what growers have done. Adjusted planting dates gradually to maximize yield potential.

That distinction is important, too. Yield potential is maximized. Are there soybeans planted June 10 that yield well? Yes. Doublecrop soybeans following wheat or vegetable crops can yield well. Or they can fail. The most important factor in soybean yield are those things that come after planting.

If you’re wondering what I specifically recommend, it’s this: plant soybeans when the soil conditions are suitable, you’re confident you’ll get an acceptable stand, and when it fits your operation’s logistical constraints. That is what early planting means to me. Below are some links to some reference articles.

Identifying Optimal Soybean Planting Dates Across the U.S.
The Soybean Flowering – Summer Solstice Fallacy
Soybean Planting Date and Maturity Group Considerations Moving into 2019
Another Look at Soybean Planting Date

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About the Author: Kevin Nelson

Kevin Nelson is a certified crop adviser (CCA) and 4R Nutrient Management Specialist (NMS) serving the ag industry in north-central Illinois. Nelson received his CCA certification in 1994 and is a Senior Agronomist with Prairie Agronomics, his independent consulting firm. Nelson has a strong background in soil fertility and precision agriculture, and he is passionate about providing information and advice to help growers be more profitable and grow better beans.