Hopefully many growers are aware of the K-State Agronomy eUpdate that comes out weekly. If not, I would suggest you take a minute to subscribe. Simply type into your internet browser box – K-State Agronomy eUpdate – and it should pull up. Once you have subscribed you will get an email each Thursday that you can click onto and read the eUpdate.
One of the articles last Thursday is on adjusting seeding rates for soybeans. Due to space limitations I will summarize it the best I can. I would suggest though if you are a soybean grower to read the full article in the eUpdate.
Seed cost is a critical economic factor, and selecting the proper seeding rate is a key management practice. This article reviews key factors in determining optimal soybean seeding rates.
Adjusting by yield environment – identifying yield potential for each environment in your field is a good practice to use when refining the soybean seeding rate decision. A recent study by Carciochi, Ciampitti, and collaborators published in Agronomy Journal evaluated soybean yield performance in a database of hundreds of experiments across the Midwest. Seeding rates ranged from 69,000 to 271,000 seeds/a, and final plant density and seed yield data were considered for the analysis. The data was classified by yield environments as follows: Low (<60 bu/a), Medium (60-64 bu/a), and High (>64 bu/a).
Main outcomes of this study were:
Most probable values. On average, optimum plant densities were:
Low-yield environments: 127,000 plants/a,
Medium-yield environments: 96,000 plants/a
High-yield environment: 97,000 plants/a.
Expected uncertainty. In 50% of cases, optimum plant densities ranged from:
Low-yield environments: 109,000 - 144,000 plants/a
Medium-yield environments: 77,000 to 114,000 plants/a, and
High-yield environments: 76,000 to 117,000 plants/a
In low-yield environments, the need for higher optimal plant density was not related to a low plant survival rate, but to a reduced potential growth rate per plant.
Another reason for the need for higher plant density in low-yield environments is that there is often less precipitation during the reproductive period in these environments, reducing the crop’s reproductive ability (reduction in yield contribution from branches).
Site-specific simulator - for site-specific management, the previous information can be used to generate prescriptions for variable rate seeding. In 2022, Kansas State University, in collaboration with the Iowa Soybeans Association, launched a free web-based simulator designed to assist farmers in implementing variable seeding rates. https://analytics.iasoybeans.com/cool-apps/SoybeanVRSsimulator/
Maintaining a fixed seeding rate for the whole field can reduce profitability compared to using a variable seeding rate, is the concluding point with more details in the full article. It goes on to explain how the profits simulation works and the interaction with other practices.
In summary, adjusting seeding rates based on plant survival rates, soil conditions, and planting dates can reduce the risk of yield and profit losses due to suboptimal densities in a low-yield environment while limiting higher seed costs due to supra-optimal densities, especially for medium and high yield environments. Soybean plant density levels above the optimal plant density increase the risk of lodging and disease development without adding a yield benefit.
If planting early, try to maximize plant survival and reduce threats to emergence by:
Avoid planting when soil temperatures are below 60°F. If planted into soils cooler than 60°F, seedlings may eventually emerge but will have poor vigor.
Treating seeds with fungicide and insecticide.
Selecting varieties with resistance to soybean cyst nematode and sudden death syndrome.
Stacy Campbell is an Agriculture and Natural Resources agent for Cottonwood Extension District. Email him at scampbel@ksu.edu or call the Hays office, 785-628-9430.
