Late Soybean Planting: Management Considerations

 

As we are nearing the end of May, the USDA-NASS reports only 6% of soybeans have been planted in South Dakota, which is substantially behind the 5-year average of 64%. While saturated soil conditions are prevalent in many areas of the state, extended weather outlooks suggest that producers may be able to return to the fields and resume soybean plantings in the near future. Should management practices change due to the late planting season?

 

 

 

Conventional wisdom says that it is not necessary to switch to earlier maturities until June 10th. However, producers that plant very long maturity group (MG) soybeans may want to switch to something earlier around June 1st. Those planting early MG soybeans should be fine until the end of June. A study from Minnesota and Wisconsin showed that yield losses for 1.5 MG soybeans only began to show significant yield losses after June 1st. The study concluded that there is little potential for higher yield based on MG selection when planting late. In addition, soybeans have the ability to ‘make up ground’ or adjust to late planting because they are photoperiod sensitive. A study from Iowa reported that the same soybean variety planted 40-60 days apart reached physiological maturity 7-10 days apart. Perhaps the most important take home is not to switch to inferior soybean genetics just to get an earlier MG.

 

 

Some agronomists like to increase seeding rate as planting is delayed to increase canopy and (in theory) boost the number of flowers/pods per acre. Researchers from Iowa, SD, and Wisconsin observed maximum yields for late planted soybeans at a planting rate of 154,000 seeds per acre, or slightly higher than the normal recommended rate of 140,000 seeds per acre. The authors were quick to point out, however, that the practical yield differences between seeding rates were not large and the difference between 140,000 and 160,000 seed per acre was only 0.7 bushels (66.6 and 67.3 bu/acre, respectively). Despite ‘iffy’ yield benefits, many producers may choose to increase seeding rates in order to increase canopy to help with waterhemp (or other weed species) pressure. If increasing seeding rate, make sure to consider extra seed cost into the decision.

 

 

Recent research in South Dakota has demonstrated that insecticide seed treatments do not provide consistent yield benefits throughout the state. The research demonstrated that insecticide seed treatments should be used in a targeted approach in areas where bean leaf beetles have an increased likelihood of causing early season defoliation, which is typically in the southeast corner of the state.

 

Despite being past the optimum planting window, there is still time to get a good soybean crop this year. Often, the weather during the growing season has a larger impact on yield than planting date alone. In a South Dakota study consisting of four locations over two years, June planted soybeans out-yielded May planted soybeans 50% of the time. While odds for high soybean yields are generally better when planting early, a well-timed precipitation event can have a much larger impact at the end of the season.