Soybean planting dates have been moving earlier and earlier. In a nod to this, the USDA Risk Management Agency has moved up the earliest planting dates for replant insurance coverage – April 10 for the southern 3 tiers of Iowa counties and April 15 for the northern 6 tiers of Iowa counties. Even with this change, there has been some experimenting with planting soybean even earlier.
Earliest planting dates for replant insurance coverage were updated ahead of the 2023 planting season. https://www.extension.iastate.edu/agdm/crops/html/a1-50.html for more information from ISU Extension and Outreach Ag Decision Maker.
The hopes of early soybean planting are faster canopy closure, more plant nodes, high pod retention, and ultimately, higher grain yields. It is true that early planted soybean will close canopy sooner and, in some situations, can begin flowering and pod setting earlier compared to soybean planted at the end of April or in early May. However, this does not always translate into higher yields.
Soybean are just as susceptible as corn to cold injury when they are planted into cold, wet soils. Soybean cold injury results in seed death before emergence or loss of seedling vigor, much like corn, however, corn will also have corkscrewing of the mesocotyl. In severe instances soybean emerged plant populations could be reduced up to 20%.
The hypocotyl and cotyledons are thick, waxy and have a high sugar content. These characteristics do allow them to tolerate frost better (down to 30 degrees) than corn leaves. However, this stage only lasts until the apical meristem (soybean growing point) begins to develop at which time soybean frost injury is much greater than corn.
Soybean planting is also influenced by corn planting. I often get asked which should be planted first, corn or soybean? Both have the highest yield potential when planted prior to May 20. After May 20, yield losses for late planting are greater for corn than they are for soybean. From this standpoint, if there is potential to be planting after May 20, corn should be given priority. If all acres can be planted before May 20, it does not really matter whether soybean or corn is planted first. This may be a situation where soybean and corn planting date can be used to increase the harvest window for soybean.
Yield potential response to planting date for corn and soybean in Iowa.
If soybeans are planted in mid-April, or earlier, there are some important considerations that can help improve plant health and yield potential.
Plant soybean into warm soils where the soil temperature will not decrease during the first 24 hours. Aim for planting in late morning or early afternoon when soil temperatures may be greater than 50 degrees. Soybean seeds imbibe water in the first 12 to 24 hours and imbibitional chilling is often associated with cold soil water temperatures during this seed imbibing timeframe.
Choose soybean varieties with high scores for early season vigor or cold tolerance, is high quality, and has a high seed germination percentage. If time allows, get a cold, saturated germination test to determine risk potential for planting into harsher soil conditions.
Account for frost and freeze damage associated with early planting dates. One benefit from planting earlier is that emergence is usually delayed too.
Increase seeding rates by 10 to 20 percent to account for emergence losses and seedling disease mortality. The ultimate goal is to have 100,000 plants per acre at harvest time.
Consider fungicidal and insecticidal seed treatments to help manage an increased risk of seedling diseases and bean leaf beetles. Fusarium, pythium, phytophthora, and rhizoctonia seedling disease risk is greater when emergence is delayed, especially in cool, wet soils. Sudden death syndrome and phytophthora can also be managed through variety selection. Insecticide seed treatments can protect against early season insects and bean leaf beetles tend to be most problematic in the first emerging soybean fields.
Regardless of when you plant your soybean, scout your earliest planted fields first to see what issues are to come. Compare plant populations from early planted and late planted fields. Identify how weed pressure is affected by changes in canopy closure. By comparing and contrasting early planted versus later planted soybean will help you determine what benefits were attained.
