In 2006, a group of farmers gathered in York for a discussion about on-farm research projects for the coming year. They were looking at ways to reduce input costs without affecting yield. One question asked was; “What is the effect of seeding rates on soybean yields?” To look at the question, several farmers chose to try a project with four seeding rates (90K, 120K, 150K, and 180K seeds/acre) in 30-inch row spacing.
Ten years later, the research continues with the same results: reducing soybean seeding rates from 180,000 or 150,000 seeds/acre to 120,000 seeds/acre doesn’t statistically reduce yields in 30-inch rows in silty clay loam and silt loam soils in south-central and southeastern Nebraska. Results of 16 studies showed for seeding rates of 180K, 150K, and 120K seeds per acre, average yields were 66.9, 66.5, and 66.2 bu/ac, respectively, which is not statistically different.
Surveys conducted via CropWatch (website) and at pesticide trainings found most Nebraska farmers planting an average 150,000 seeds/acre. Our recommendation, based on our research, is to consider reducing the soybean seeding rate to 120,000 seeds per acre and aiming for a final plant stand of 100,000 plants per acre.
Economically, if you dropped your seeding rate from 150,000 to 120,000 seeds per acre, you would save $10.69/acre (Assuming a $60/bag seed cost at 140,000 seeds).
The same question, regarding the effect of reduced populations on soybean yields, exists today for farmers switching to narrow-row soybeans. In 2016, two on-farm research studies were conducted in Richardson and Washington counties with 15-inch row soybeans.
Seeding rates of 90K, 120K, 150K, and 180K seeds/acre were planted in the Washington County field with non-significant yield differences of 76, 77, 77, and 76 bu/ac respectively with the 90K rate resulting in the highest marginal net return. The farmer was able to achieve 91% or greater of original planted stand.
Seeding rates of 116K, 130K, 160K, and 185K were planted in the Richardson County field. There were no statistical yield differences between 185K, 160K, and 130K seeding rates in this study with yields of 68, 68, and 67 bu/ac respectively. The 116K seeded rate resulted in a yield of 66 bu/ac. Heavy crusting affected final plant populations in the field, resulting in final stands of 87,667, 99,417, 113,667, and 126,333 and for seeding rates of 116K, 130K, 160K, and 185K, respectively. The 116K seeding rate resulted in the highest marginal net return for this study.
Let’s be clear about the bottom line here – Nebraska research shows reducing the soybean seeding rate from 150,000 to 120,000 seeds/acre can result in a $10.69/acre savings without affecting yield.