The foundation upon which all soybean management decisions should rest is product selection. The use of the best-adapted product along with proper fertility, planting practices, and stress management can help set the stage for maximizing yield potential. Weeds, insects, diseases, nematodes, and other manageable agronomic and environmental factors should be addressed.
Maximizing soybean yield potential is determined by the interaction of many agronomic and environmental factors. Selecting the best-adapted product for each field is a fundamental step toward accomplishing a yield maximization goal. After seed selection, aside from non-controllable weather related issues, the management of inputs and agronomic factors are keys toward the production of a well-podded and disease free soybean crop (Figure 1).
Product Selection: Selecting the best-adapted product for a field should be based on the history and characteristics of each field along with the genetics, maturity, and traits of available products. Product ratings should be reviewed closely to address potential disease, weed, nematode, and standability issues.
Planting Date: If early soil and weather conditions are favorable, an earlier planting date has the potential to add bushels.1 Earlier planting can produce a quicker canopy which can help plants utilize solar radiation for energy production throughout more of the growing season. As a result, more nodes can be produced on the main stem which can increase the potential for more pods and seeds/plant. The University of Wisconsin has reported average yield decreases of 0.4 bu/acre per day when planting was delayed past the first week of May.1 Additionally, the University of Nebraska reported an average decrease of 0.6 bu/acre per day that planting was delayed after May 1 under good growing conditions.1
Early planting can also help conserve soil moisture and reduce potential wind and water erosion. Early planting may not be as favorable in fields with a history of holding excessive moisture because of diseases that favor wet soils, such as sudden death syndrome and phytophthora.
Planting Conditions: Soybean seed should be planted 1.25 to 1.75 inches deep into a moist seedbed with good seed-to-soil contact for germination.2 Soybean seed can begin the gemination process when soil temperatures are around 50° F; however, it is recommended to plant when soil temperatures at seeding depth are in the 50’s and trending upward. Planting into seedbeds that are too wet can result in poor seed placement, stand establishment, and compaction.
Row Spacing: Research has shown that row spacings narrower than 30 inches can help improve yield potential.2 Narrow rows can close the rows quicker which helps: 1) intercept more sunlight for photosynthesis, 2) keep weeds from growing, and 3) conserve available soil moisture.
Seeding Rates: A seed product’s seed size, plant height, ability to branch, disease tolerance or resistance, germination percentage, and standability rating should be among considerations when determining seeding rates. Economics (seed cost) is another consideration. Studies have demonstrated that potential yield increases attributed to higher seeding rates is small above 100,000 seeds/acre.3 However, in some situations such as planting into poor seedbeds or more weathered soils, higher seeding rates may be desired. Soybean plants have a great ability to compensate for lower populations by producing more branches which can set more pods. Final stands of 50,000 plants/acre uniformly spaced have produced yields equal to much higher populations.2
The goal is to have a uniform population of equally spaced plants at harvest. Seed treatments, such as Acceleron® Seed Applied Solutions should be considered to help protect seeds and seedlings from fungal pathogens, nematodes, and insect pests that have the potential to decrease plants/acre.
Nutrient Management: As soybean yield potential increases, a well-fertilized previous corn crop may not supply adequate fertilization for the following soybean crop. Therefore, the need to manage soil fertility becomes essential. Soil sampling is an important part of a nutrient management plan to determine soil pH and the amount of soil-available nutrients. A soil pH of 6.5 is considered to be appropriate level for the release of soil nutrients for soybean growth.
Although soil tests can provide a good idea of the availability and amounts of most nutrients, they do not provide an accurate picture of available nitrogen (N). Because soybean plants can acquire up to 75% of their N requirements from the air when N-fixing bacteria are active on soybean roots, it is important to first determine whether there is a presence of the N-fixing bacterium Bradyrhizobium japonicum in the soil. In general, if a soybean crop has not been grown in a field for 3 to 5 years or more, seed inoculation is recommended.
The remainder of the N must come from the soil or supplemental N provided to the plant. Supplemental N may be a consideration on the most productive fields or in cases where the following conditions may warrant its use: 1) soil is light colored, eroded, or compacted, 2) soil has a pH lower than 5.5, 3) crop shows N deficiency symptoms, or 4) active nodules cannot be found on roots. Efficiency of the nodules providing N to the plant tends to decrease during the later reproductive growth stages when N requirements are high.4 If supplemental N is needed, half can be applied before flowering begins and the rest at the beginning of pod filling to help assure the availability of N at critical stages.
One of the biggest challenges that farmers face trying to improve soybean yields is stress management. Stress can appear in the form of weeds, insects, diseases, nematodes, and a whole host of environmental factors. While a soybean crop seems to tolerate short periods of stress better than other crops, any extended stress as plants reach reproductive stages can impact the ability of plants to recover and salvage yields.
Weed Control: Soybean plants are relatively resilient in terms of weed competition; however, yield loss due to inadequate weed control still occurs. For optimum weed control, weeds should be managed early and completely using Roundup Ready PLUS® Crop Management Solutions. Begin with a preemerge program, followed by a postemerge program that controls herbicide-resistant weeds. Be sure to consider proper timing and application rates and use herbicides with residual activity and multiple sites of action when possible. For best results, eliminate weeds prior to planting and control new weeds when they are small. Scout and monitor fields throughout the season for weed escapes. Weeds should be controlled so they don’t set seed prior to harvest and create future weed control problems in following seasons. Consider rotation to other crops in future seasons to allow for the use of different weed management and cultural practices. For more information about weed management solutions, visit www.roundupreadyPLUS.com
Scouting: Insects, diseases, and nematodes can all have a negative impact on soybean yield. Because these can vary greatly across different geographies and field environments, it is beneficial to know each field’s risk factors. For example, soybean cyst nematode (SCN) is a pest that cannot be eliminated from a field once established; however, management techniques can be employed that can help protect yield goals.
Scouting can be done by walking a random path through the field and stopping at various locations throughout to look for weeds, insects, damaged leaves, diseases, and nutrient deficiency symptoms. Record your findings for reference later in the season as well as during successive seasons. Scouting for insect infestation and damage should continue through the R7 (beginning maturity) stage as yield-robbing insects such as bean leaf beetles and two-spotted spider mites may still warrant control through seed fill.
Treatment thresholds vary by geographical areas, weed heights, flowering dates, and other factors. Therefore, consult your local Channel Seedsman or university specialists for control recommendations. Seed treatments, such as Acceleron® Seed Applied Solutions should be considered to help protect seeds and seedlings from fungal pathogens, nematodes, and insect pests.
1Staton, M. 2011. Planting soybeans early offers many benefits. Michigan State University Extension. http://msue.anr.msu.edu
2Nafziger, E. Chapter 3 Soybean. Illinois Agronomy Handbook. University of Illinois. http://extension.cropsci.illinois.edu/handbook/
3Licht, M. 2008. Soybean plant population. Integrated Pest Management. Iowa State University Extension. http://extension.agron.iastate.edu
4Ferguson, R.B., Shapiro, C.A., Dobermann, A.R., and Wortmann, C.S. 2006. Fertilizer recommendations for soybean. University of Nebraska, Lincoln. NebGuide G859.
Additional sources: Illinois soybean production guide. 2012. Illinois State University and Illinois Soybean Association. Pedersen, P. Row spacing in soybean. Iowa State University Extension. http://extension.agron.iastate.edu