By Jim Specht
Numerous soybean seeding rate studies have indicated that a final plant population of about 80,000 to 120,000 plants per acre is likely sufficient for ensuring an economic return, with the latter being based on weighing the slightly higher yield potential with higher final plant populations against the cost of planting more seed/acre to get to higher plant populations than this range.
For example, if your goal is to have 100,000 plants per acre at harvest, you will need to adjust your seeding rate accordingly for two factors.
One adjustment accounts for the fact that it is rare to have a bag of seed with 100% seed viability. Check the seed bag tag for the official germination percentage. It may be 98%, 95% or perhaps even 90%.
The second adjustment accounts for the fact that not every germinated seed will result in an emerged seedling, and not every emerged seedling will survive the season to become a final mature plant. A review of the literature indicates that, on average, the seedling and plant survival percentage is about 85%. You can choose a different percentage to suit your experience and the field condition the day you plant.
To adjust for these factors, multiply the decimal equivalents of the two percentages (for example, 95% germ and 85% survival). Thus, 0.95 x 0.85 = 0.8075. Now, divide 100,000 by that decimal number: 100,000 / 0.8075 = 123,839 seeds/acre. Rounding that number to 125,000 seeds/acre gives you a seeding rate that is likely to get you to your goal of 100,000 plants/acre.