When we think about maximizing soybean performance, there are many agronomic factors to consider. Agronomists usually discuss variety selection, varietal maturity, seed treatment, seeding rate, planting depth, fertility, pest and weed control, and planting date, to name some of the key factors. In this article, I am going to focus on the importance of planting date and how it impacts soybean performance.

When analyzing long-term Practical Farm Research (PFR)® data that evaluates soybean planting date and its impact to yield, we find that earlier planting (April through early May) provides a significant advantage over later planting dates.

As we consider crop production yield factors, it is usually best to focus on the largest yield-limiting factors. For many, the first factor that comes to mind is water, as it is often the most yield-limiting factor to manage in some areas of the US. However, I believe water is NOT the most yield limiting factor in many of those areas. Where water stress is less of a concern, sunlight, and its impact on the development of soybean plants, can become one of the most over-looked factors that limit yields.

Soybean plants are highly sensitive to the length of summer nights. Fluctuations in the length of the dark period triggers changes in soybean plant development, resulting in the development of reproductive structures at each soybean node. Typically, soybean plants add a new node every 3.7 days after the first trifoliate stage until approximately the R5 growth stage of development. Each node equals more flowers, pods, and eventually, grain. A 14-day delay in planting can result in the loss of four nodes! Earlier planted fields have the potential for more nodes. Earlier planting also aids in providing better weed control through crop competition, which results in less yield reduction from weed pressure. Varieties today flower approximately one week earlier and remain in the R1-R6 growth stages up to 14 days longer, than historical varieties. As stated above, earlier planting allows for earlier development of a more robust plant factory to improve the plant’s ability to harvest light and convert it into the carbohydrates, which builds greater yields. Delayed planting results in a shorter overall season with less resource development because of reduced nutrient uptake and photosynthesis. By planting earlier, we maximize the advantages provided by modern genetics.

Another advantage to earlier planting is the improvement in light quality and quantity that we can harvest due to the placement of the sun early in the summer. Prior to the summer solstice, the intensity of the light continues to increase. Daylengths are longer and the depth of atmosphere that the light must penetrate before it reaches the surface of the earth is less, until we reach the first day of summer. This results in more of the soybean plant’s life cycle occurring during the period of greatest light intensity.

As an example, when we plant double crop soybeans, we are typically planting after the summer solstice. Those fields are automatically at a disadvantage compared to earlier planted fields because they will never have light that is as energetic as the light available earlier in the season. This reduced light intensity and shortened growing season highlights the information in this article to help explain why earlier planting dates provide higher yields.

Again, many factors have a significant influence on soybean yield, but don’t overlook the importance of planting date and sunlight capture. If planting conditions are favorable, risk of significant damage from freezing has ended, and diseases such as Sudden Death Syndrome (SDS) have been accounted for, moving planting dates earlier should allow you to improve your farm’s long-term soybean yield.