Determining Soybean Seeding Rates

To the casual observer, growing a soybean crop is easy, simply plant, spray, and harvest.  However, what the casual observer doesn’t see is the crop management decisions that take place before a soybean seed is planted. These decisions often start towards the end of the previous growing season and continue to the time the planter reaches the field the following spring. Choosing an appropriate soybean seeding rate is one crop management decision that seems easy to make, but when you take a minute to think about it, there are numerous factors to consider.

It is well known that a harvestable stand of 100,000 healthy, evenly spaced soybean plants is needed to maximize yield potential and profitability. However, it is important to remember that emerged soybean stands are often 10 to 20% less than the seeding rate used.1  A seeding rate of 140,000 seeds per acre is typically the maximum seeding rate recommended for soybean seed possessing a 90% warm germination score treated with a fungicide and insecticide seed treatment, such as Acceleron® Seed Applied Solutions Standard, and planted into good seedbed conditions.  Increasing the soybean seeding rate above 140,000 seeds per acre is usually recommended if seed quality is poor, if planting into a poor seedbed, or if a fungicide and insecticide seed treatment is not used.

Soybean planting technology has improved seed singulation and planting depth control to the point most farmers that once used a grain drill to plant soybean seed have abandoned them in favor of their row-crop planter. This has made 15-, 20-, and 30-inch rows the predominate row spacing used for soybean in my geography of northern Iowa. Interestingly, research suggests there is no need to vary soybean seeding rates when planting these row widths.2

Row width and seeding rate can influence soybean plant height (Figures 1 and 2).  Wider row widths result in closer plant-to-plant spacing compared to narrower row widths planted at the same seeding rate. As plant-to plant spacing decreases, plant-to-plant competition for resources such as sunlight and space increases, which can result in taller plants in wider rows.

Measuring soybean row width. Figure 1. Measuring soybean row width. Row width and plant height are just a couple of the many factors to consider when determining soybean seeding rates.
Measuring soybean plant height. Figure 2. Measuring soybean plant height. Row width and plant height are just a couple of the many factors to consider when determining soybean seeding rates.

Product selection plays another important role when determining an appropriate soybean seeding rate because plant characteristics such as plant height, standability, and disease tolerance can influence the seeding rate used. Soybean products that are inherently tall might be prone to greater lodging risk, but in my experience, the standability score is a better indicator for lodging risk than plant height. Growers may want to plant soybean products possessing poorer standability scores into a row width narrower than 30 inches, or plant them at a slightly lower seeding rate. Both tactics should help increase soybean stem diameter, which may help improve standability at harvest.

Soybean product tolerance to disease, especially tolerance to white mold, might influence the soybean seeding rate used by growers that have a history of this disease in their fields.  Wider row widths and/or lower seeding rates resulting in lower plant populations can delay canopy closure and encourage better air circulation among the soybean plants and create an environment that is less favorable for white mold infections to occur.

Although, row width and lower seeding rates can help delay the onset of a white mold infection, they cannot prevent an infection from occurring, if the conditions of the disease triangle are met (suitable host, presence of white mold inoculum, and favorable environmental conditions for infection). However, these tactics can be combined with soybean product selection by choosing a product that has a good white mold tolerance score and using crop protection products labeled to suppress white mold, such as Delaro® fungicide and Delaro® Complete fungicide.

Land rollers have become popular over the last twenty years, and many soybean acres are rolled shortly after planting. Land rollers flatten the soil surface and push rocks, corn root balls, and clods into the soil, which makes the combine ride during harvest much smoother and allows the combine operator to keep the cutting bar of the soybean platform closer to the soil surface resulting in fewer soybean pods missed or cut open. Soybean pod height above the soil surface can vary based on the seeding rate used with pod height tending to increase as the seeding rate increases. Therefore, the use of a land roller may be one factor growers consider when determining their soybean seeding rate.

Remember, there several factors to consider when selecting a soybean seeding rate, but ultimately, a harvestable stand of 100,000 healthy, evenly spaced soybean plants is the goal to maximize yield and profitability. Your Channel Seedsman can help you determine appropriate soybean seeding rates for your fields to achieve that goal.

Paul Parcher

Sources

1Anderson, M., Vittetoe, R., Licht, M., and Rieck-Hinz, A.. Stand assessments – soybean. Integrated Crop Management. Iowa State University Extension and Outreach, Ames, Iowa. https://crops.extension.iastate.edu/encyclopedia/stand-assessments-soybean

2Licht, M.  Soybean plant population. Integrated Crop Management. Iowa State University Extension and Outreach, Ames, Iowa https://crops.extension.iastate.edu/encyclopedia/soybean-plant-population

Websites verified 10/9/22.

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FOR SOYBEANS SEED TREATMENT PRODUCTS APPLIED DOWNSTREAM, EACH ACCELERON® SEED APPLIED SOLUTIONS OFFERING is a combination of separate individually registered products containing the active ingredients: BASIC Offering: metalaxyl, penflufen and prothioconazole. STANDARD Offering: metalaxyl, penflufen, prothioconazol and imidacloprid. FOR UPSTREAM TREATED SOYBEANS, EACH ACCELERON® SEED APPLIED SOLUTIONS OFFERING is a combination of separate individually registered products containing the active ingredients: BASIC Offering: metalaxyl, fluxapyroxad, and pyraclostrobin. STANDARD Offering: metalaxyl, fluxapyroxad, pyraclostrobin and imidacloprid. Not all products are registered in all states and may be subject to use restrictions. The distribution, sale, or use of an unregistered pesticide is a violation of federal and/or state law and is strictly prohibited. Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields. Not all products are registered for use in all states and may be subject to use restrictions. The distribution, sale, or use of an unregistered pesticide is a violation of federal and/or state law and is strictly prohibited. Check with your local dealer or representative for the product registration status in your state. Channel® and the Arrow Design® and Seedsmanship At Work® are registered trademarks of Channel Bio, LLC. Acceleron® and Delaro® are registered trademarks of Bayer Group. All other trademarks are the property of their respective owners. For additional product information call toll-free 1-866-99-BAYER (1-866-992-2937) or visit our website at www.BayerCropScience.us. Bayer CropScience LP, 800 North Lindbergh Boulevard, St. Louis, MO 63167. ©2022 Bayer Group. All rights reserved.

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