June 12, 2009
Assessing Post-Storm Soybean Stands
(Extension specialists have recommended reprinting the following story published in the May 28, 2004 CropWatch. It was written by Roger Elmore, who was an extension crops specialist at the South Central REC and is now an extension corn specialist at Iowa State University.)
Consider several factors when assessing the minimum stand necessary to achieve reasonable yields. The expected yield loss from the reduced stand must be balanced against the anticipated yield loss from replanting after the optimum planting date (mid to late May). Leaving a poor stand may result in poor weed control or increased herbicide costs. Replanting entails additional costs for seed, tillage, and replanting in addition to the potential yield penalty imposed by a later-than-normal planting date.
Obtaining stand counts is the first step to assessing the field situation. Count plants that have a good chance of recovery. Emerged soybean plants can recover from stem damage if the stem is not severed below the cotyledonary (seed leaf) node. This is the first node on the seedling; the two fleshy-like cotyledons are attached to this node. If still present, buds on each side of this node can produce regrowth. If the plant is broken off below this node, it will not survive.
Once stand counts are established, refer to Figure 1 to estimate plants/acre. Although yield is reduced when plant populations fall below 100,000 plants per acre, the yield loss is not proportional to stand loss. A general guideline is to leave a field alone if plant populations are greater than 50,000 plants per acre, the stand is uniform, and the field can be kept weed free.
If replanting is necessary, what seeding rates and other practices are recommended?
- Use a narrow row spacing, if possible, and higher seeding rates to hasten canopy closure since soybeans planted in June are usually shorter . Faster canopy closure will suppress weeds.
- Avoid using very early maturing varieties because they will flower quickly, resulting in short plants. Tall, medium maturing varieties for your area offer the best hope of minimizing potential yield loss from planting late.
- Don't plant non-adapted, early-season varieties.
These recommendations apply to double-cropped soybeans as well.
See Soybean Seeding Rates (NebGuide G1395) for recommended soybean seeding rates, stand assessment, and replanting rates.
Extension Crops Specialist
South Central REC