By Dr. Harold Willis
To achieve a desired soybean plant population, you need to calculate the number of seeds required. Some seeds will not germinate, and some that germinate will not become established because of weather, pests or disease. Generally, if the seedbed and planter are good, about 90 to 95% of germinated seedlings will become established. To figure planting rate, use this formula:
You need to plant 7.9 seeds per foot of row to get six plants per foot. Since soybean seed is usually sold by weight rather than by number of seeds, you need to know the number of seeds per pound to figure pounds needed per acre. If the seed dealer cannot give you number of seeds per pound, weigh a few one-ounce samples on a postage scale to get an average figure.
The number of linear feet of row per acre can be found from the accompanying table. Then figure the pounds of seed needed per acre:
Calibrate your planter accordingly and check seed drop in the field regularly.
Soybean Planting Depth
Soybean seeds should be planted deep enough to absorb enough moisture to germinate, but not so deep that they have trouble emerging from the soil. Some varieties can emerge from greater depths than others. Typical planting depths are 1 to 1½ inches, but if soil is low in moisture or sandy, plant 2 inches deep. In cool, moist soil seed can be planted 1 inch deep if there is no danger from herbicides.
Soybean Planting Method
Best results are obtained using a unit planter or grain drill to plant in rows. Drills usually do not handle rough seedbeds as well as planters. Broadcasting or aerial seeding followed by light tillage to cover seed often results in uneven emergence and stands that are too thin in some areas and too thick in others.
If a stand of soybeans is reduced by disease, pests, hail, flooding, herbicide injury, etc., replanting may be considered. If the loss is covered by crop insurance, consult your insurance agent first. If most of a field is lost, be sure enough growing season is left for beans to mature.
If the surviving population is 75% or more of the desired population, replanting is not necessary (unless weeds will be a problem) since the surviving plants will branch out to fill in gaps.
When replanting, you may want to use shallow tillage to kill young weeds. Do not apply herbicide. Use a variety with maturity date appropriate for the later planting date, increase the seeding rate by 10 to 15% and plant in narrow rows to increase yield.
Source: How to Grow Super Soybeans