Agronomy: How Soybeans Respond to Late Planting

Spring planting is still a couple months away, but inevitably, some farmers in Illinois will have to deal with a wet spring, which delays planting corn and soybeans. While both corn and soybeans benefit from early planting, the yield drag is greater for corn with late planting.

Historically, in Illinois it seemed that when the calendar flipped to May, growers knew it was time to think about seeding beans. Of course, if you wait until May to start and then it rains for the first three weeks, you are stuck planting into late May and June, which is something no farmer relishes.

Growers know that no matter when they plant in May, they could have an ideal summer and a warm fall that will help compensate for late planting. Once in a while that happens. But when you get into June, that isn’t the case, it is just late and the plant just doesn’t get big enough to produce desire yields. That is why agronomists recommend narrow row spacing and higher populations on later planted fields. You just need more plants to offset yield losses because the plant can’t compensate accordingly.

Narrowing row spacing is difficult if you only have a 30-inch planter. However if you have access to a split planter (15inch for beans) or drill you can narrow the rows while increasing the population 10 to 15 percent for late May plantings and 20 to 30 percent when planting in early to mid-June. If you find yourself having to plant in late June, manage full-season beans like double-crop beans, which may mean a 50-percent increase in seeding rate.

Soybean yield is mainly about pod set per plant and less about seed number and size, though they do contribute to yield. Generally speaking, the earlier you plant, the more nodes are produced on the main stem, the greater number of branches and total pod sites on the plant and the greater the yield potential. Also, the earlier you plant means the plant will start to flower earlier. A general rule of thumb is that for each week you plant earlier than May 1, a few flowers will show up before summer solstice in June. Not great numbers of flowers, but it will start flowering sooner, which means more pods set. And remember that adding one more pod with two beans per pod per plant is worth two additional bushels per acre.

Of course one can question how important adding extra pods is since soybeans routinely abort about 50 to 60 percent or more of their flowers and pods due to stress or their inability to feed them. However, it is true that a good portion of pods set weekly will survive to the end, so the earlier pod set starts, the greater the survival and yield. But in the end a lot still depends on the season.

Of course there are “popular” ways to encourage more branching and pod-setting sites and those include rolling beans, applying a lactofen herbicide (Cobra®) or applying plant growth regulator products such as Stoller’s Bioforge® or other growth stimulants at V2 or V3 stage. So even if you plant a few days or weeks later, these types of treatments may help the plant compensate for late planting by setting more nodes or pod sites. However, the data on whether these approaches work isn’t consistent yet so you have to make this decision based on your own instincts and experience.

At the end of the day, soybean yield is really about pod count, and the more pods we produce and keep, the greater the yield. Do you have any strategies you deploy to increase pod set on your soybeans or do you leave it up to Mother Nature to determine it for you?

Drop in a comment below and let us know what strategies you plan to adopt to maximize bean yields and if you will end up planting outside the optimum window in May or just late in June?

Agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com