By Shaun N. Casteel
This planting season has been another trying one for many of the state. Over the month of May, we were waiting for field conditions to improve enough for field preparations and planting. The calendar and workload weighed on many, so fields were worked a touch early and soybeans were planted in less than ideal conditions. Soybean stands are subpar in countless fields from “mudding in” (open seed slots) to “clodding in” (fields worked wet and seeds are in contact with clods instead of soil, Figures 1 and 2) with no more rain. While other fields dried out by Memorial Day, and soybeans were planted into decent seedbeds just to have a pounding rain within a day to prolong the dampening off conditions followed by hot temperatures to form crust.
Figure 1. Spotty stand of soybeans due to cloddy seedbed conditions followed by limited rainfall to make up for the poor seed-to-soil contact.
Figure 2. Uneven emergence of soybean due to variable seed depth under cloddy soil conditions and lack of moisture.
Needless to say, many soybean fields are in dire straits as we assess stand establishment. Our normal goal is 100,000 to 120,000 plants per acre to optimize yield. However, we should not be quick to replant or overseed into an existing stand if the field is less than 100,000. Obviously, the distribution of plants at suboptimal stands will factor into the decision to replant. Approximately 70,000 plants per acre is the gray area for replanting. If there are pockets that are much lower than 70,000 plants per acre, those can be filled in.
Figure 3. Hula hoop method determined stand of 90,000 plants/acre. No replant needed.
Stand assessments need to count emerged soybeans AND the potential seeds or seedlings that may emerge. The below ground factor and weather forecast will play into these decisions. If the missing plants are due to seeds that have rotted below ground or the hypocotols and cotyledons have snapped off, then the stand is what you have to work with in that field. Whereas, seedlings near the soil surface that need a softening rain could be the reinforcements that is needed for subpar stands.
The replanting operation will cause damage to the established plants (nearly 20% stand loss when overseeding with a 30-inch planter at an angle) and you still at the mercy of Mother Nature to have the replanted seed establish plants. Young soybean plants (VC stage, cotyledons and unifoliates) are sensing light quality to determine the need for branching out. Basically, if a soybean plant has few neighboring plants (little to no shading), branches are initiated to fill the void literally and produce pods on those branches. As we get later into June, these soybeans in subpar stands will have minimal branching due to “pushes” from the photoperiod. Replanting into stands of soybeans that are V2 (two unrolled trifoliates) often become more cosmetic early if the overall stand was above 70,000 plants per acre.
Replanting recommendations will be field specific, but factors to consider are seeding rate, maturity group, planting pattern, and weed control (see Late Planting and Replanting of Soybean).