Maximizing Soybean Yield Potential

An Illinois Soybean Association 100 bushel Yield Challenge record was established in 2015 when a Champaign County farming operation obtained a 108.3 bu/acre yield in the checkoff-funded contest.1 Agronomists, researchers, and farmers are continually researching and testing ways to maximize soybean yield potential.

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Yield maximization is a factor of agronomic and environmental factors including genetics, planting date, row spacing, plant population, fertility, pest management (weeds, diseases, insects), scouting, and available water. Several of these factors contributed to the new record.

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Product Selection (Genetics)

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One recommendation for maximizing yield potential is to utilize a full season seed product with desirable agronomic traits for the area. Full season products have the ability to fully utilize the available sunlight for the growing season to optimize photosynthesis. The record was set using Asgrow® AG4135 brand, a 4.1 maturity product with Rps1c resistance and moderate field tolerance (likely more effective in Illinois than the single gene) for phytophthora root rot, a disease common to central Illinois because of its soils and rainfall amounts. The product also has R3 resistance to cyst nematode (SCN), and excellent ratings for emergence and standability. Soil testing for SCN races or HG type(s) should be accomplished to help determine the need for SCN resistant products. Products rated high for emergence have demonstrated the ability to potentially emerge more easily under stressful conditions. Products with excellent standability are less likely to lodge, allowing for an easier harvest and reduced chance of lost seed due to the inability to fully harvest lodged plants.

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Planting Date

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The contest winning field was planted April 23, generally within the defined prime corn planting timeframe for the area. Researchers at the University of Wisconsin found that soybean yields decreased by 0.4 bushels per acre per day when planting was delayed past the first week of May.2 Planting soybeans earlier allows for earlier canopy closure which can help increase yield potential. This can maximize light interception and capitalize on a longer period for photosynthesis. It can also lead to an increase in the number of plant nodes, earlier flowering, a longer reproductive period, and an increased crop growth rate during pod set leading to a greater seed filling rate, and earlier harvest. In addition, early canopy development can help in conservation of soil moisture, which is critical during reproductive periods.

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When planting early, it is important to wait until good soil and seedbed conditions exist as soils that are too wet may result in compaction, poor seed placement, and reduced stand establishment. Additionally, seeds planted in cool, wet soils may remain dormant and can become more vulnerable to diseases, insects, and feeding by animals and birds. Planting soybean seed into wet soils will likely negate any yield advantage from planting early.

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Narrow Rows

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Research has shown that narrow rows (less than 30 inches) yield greater than wide rows (30 inches or greater).3 A 20-inch row spacing was used in the record-setting Champaign County field. Narrow rows help promote quicker canopy closure, which can help improve light interception, weed control, and soil moisture retention. An Iowa State University study showed an average 4.5 bu/acre increase using 15-inch row spacing, compared to 30-inch row spacing.3 A Monsanto demonstration trial showed that 30-inch twin rows provided a yield advantage over conventional 30-inch rows.4 The attraction of the twin row configuration is based on the ability to utilize the same planter for corn and soybean, utilize 30-inch harvest equipment for corn, and possibly realize a benefit in soybean similar to what would be expected in narrower rows.

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Plant Population

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Higher plant populations have some advantages including quicker canopy closure, greater light interception, and decreased weed competition. However, yield does not always increase as soybean plant population increases.

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To help maximize yield potential, growers should have no less than 100,000 plants per acre in 7.5- and 15-inch rows and no less than 80,000 plants per acre in 30-inch rows.5,6 Iowa State University recommends a 15 to 30% increase in seeding rate over the desired final plant stand to compensate for any plant loss resulting from crusting, hail, or other causes.5

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Nutrient Availability

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Soil tests are an important management tool for determining soil pH and fertility needs. Use soil tests to determine whether the pH is in the proper range for nutrient availability and to assess phosphorus and potassium needs.

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Soybean plants obtain 50 to 75% of nitrogen (N) requirements from the air when Rhizobium bacteria are present in the soil. The remainder of the N must be supplied from soil mineralization. Seed inoculation with Bradyrhizobium japonicum can increase N fixation and may improve yield potential.

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When the supply of soil N and N-fixing nodules is not adequate, the addition of foliar N from late vegetative through pod fill growth stages may be beneficial.

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Pest Management

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Soybean yield can be negatively impacted by insects, fungi, bacteria, viruses, nematodes, and weeds. In general, an integrated pest management (IPM) approach is the most economical way to protect yield potential while limiting input costs and environmental hazards. An IPM approach utilizes host resistance with biological control, pest monitoring, chemical control when thresholds are reached, and good agronomic management practices to help avoid yield loss. Management decisions are usually made on a field by field basis and control tactics depend on the presence of particular pests, diseases, or weeds. When specific soil borne diseases and early-season insects are expected because of historical information, seed treatments such as Acceleron® Seed Treatment Products for soybeans can be a proactive course of action.

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Season long weed control is important. Preventing early season weed competition can encourage early canopy development, thus helping to maximize soybean yield potential. Plants that develop canopies early may have an increase in flowering period and number of main-stem nodes. Multiple overlapping residual herbicides are a key component of season long weed control. Consider targeted weed species, rate, site-of-action, tank-mix options, and timing when using residual herbicides.

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Agronomic Resources

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Your local Asgrow® brand dealer is a vital source for agronomic information. Along with other information, they can help with product selection, scouting information, and weed control recommendations. The new record holders cited and were thankful for the availability of professional resources.