Behind Planting My Full Season Soybeans: What Maturity Group Can I Use?

By Rachel Vann

Many growers are now planting soybeans later than they intended to. Whether it is because wet weather prevented fields from getting planted in the first place or excessive wet weather is requiring a replant on soybean or cotton acres, questions are emerging about what maturity group can be used at this point in the planting season.

• Optimal maturity group for late May/early June planting: What does our preliminary planting date data suggest? Last year across the state, we saw our highest yields with a late MGIV and mid MGV planted from mid-April through mid-June. I will emphasize this was a late MGIV (4.9) and one year of data. We have limited information on planting an earlier maturing soybean variety as we move into June planting dates because this has not traditionally be done in North Carolina. More information will be generated in the next few years on this topic.
• What do we know from our NC State University OVT data? We are somewhere between our typical planting dates for the full-season and double-crop soybean OVT tests. Data from this program over the past several years indicates that a high-yielding soybean variety can be selected from a MGIV to MGVII for planting both full season and double crop, but the full season trends over the past three years have leaned towards higher yields with a MGIV and V then later maturing varieties when planted in the middle of May. Double crop results have been variable, with a flat yield response to MG in two of the past three years, meaning growers have some flexibility in planting a mid MGIV to MGVII in a double-crop situation. A excellent tool has been developed by the NC Soybean Producers Association using the NC State OVT Soybean data to aid in soybean variety selection.
• Can I plant a maturity group earlier than a mid-IV at this point in the season? I have had a few questions about planting earlier than a mid MGIV at this point in the season. I am hesitant to recommend this now and as we move into a double-crop situation. Soybean flowering is triggered by an interaction between photoperiod (night length) and temperature. When we start planting MGIII and early MGIV soybeans at this point in the season, the night length required to trigger flowering will occur quickly after planting, potentially not leaving enough time for vegetative growth prior to flowering. If you were around the Raleigh latitude and you planted a MGIII.7 to MGIV.2 that emerged on June 6, it is predicted using the SoyStage tool developed out of the University of Arkansas that these soybeans would only have a month for vegetative growth prior to flowering. If you plant a MGV.2 to MGV.7, it is predicted you would have six weeks for vegetative growth prior to flowering. As Dr. Dunhpy consistently emphasized, we want our soybean tall enough to lap the middles. As we delay planting, the use of an earlier maturing variety decreases our chance of having enough vegetative growth to lap the middles.
• Be ready for timely harvest: Using this information if you decide to plant an earlier maturing variety than you typically use at a later planting date, you need to be ready to harvest when the soybeans are ready. Timely harvest of earlier maturing varieties is critical to protect seed quality.
• A few things to consider for soybean replant: 1. For May planted soybeans, you are at maximum yield potential if you have 75,000 plants/A; that number is 90,000 plants/A for June planted soybeans. Get an accurate assessment of stand before making replant decisions, especially as we push into June planting. It has been documented in the mid-Atlantic region that after mid-June planting, we are losing ½ bu/A with each day delay in planting. The pros of replanting must outweigh the potential yield declines from delayed planting.

Other things to look out for right now: cooler-than-normal and wet weather synergizing herbicide injury and seedling diseases. I have seen many soybeans fields across the state off to a very slow start this year. That is going to result in reduced canopy competitiveness with weeds. Growers should be alert at scouting for early season soybean issues. Consult your County Extension agent if you have questions about early season soybean issues.