- Soil conditions, weather, planting date, and cultural practices all have an effect on soybean emergence.
- Cloddy, compacted, or crusted soils are some scenarios to watch out for when planting soybeans because they can result in reduced emergence.
- In order to help maximize yields, soybean seeds should be planted with uniform seed spacing and seeding depth.
Soybean emergence can depend on soil conditions, weather, planting date, and cultural practices used, such as planting depth, tillage, and seed treatments (Figure 1). Soybean plants have a favorable response to early planting under ideal soil conditions. Regardless of the planting date, the goal is for the soybean crop to reach canopy closure (fill in the row middles) prior to flowering. An early canopy can result in better yields due to a more efficient use of sunlight. Late soybean planting can result in yield losses ranging from 1/4 bushel to more than 1 bushel per acre per day depending on the row spacing, planting date, and plant type.1 Planting delays can reduce the pod number, and therefore yield per acre. If planting late cannot be avoided, be sure to plant a late-maturing product that will reach physiological maturity before the first killing frost.
Weather and Environmental Conditions
Temperature. Soybean plants can germinate when the soil temperature at a 2-inch depth is 50° F, but cooler temperatures can slow germination up to 3 weeks.2 The optimum soil temperature for soybean germination is 77° F, but often this temperature is not met until after the ideal early planting window for soybean has passed.2 Warmer temperatures will result in a faster germination rate and seedling growth.
Generally, planting earlier in cooler soils can result in slower emergence, but yield potential is usually not impacted. That being said, it is important to consider seedbed conditions if planting early. Although adequate moisture is needed to initiate germination, planting into a seedbed that is too wet can lead to reduced emergence which may reduce yield potential. Because root development is slow in cold soils, soybean plants may be more susceptible to root rot pathogens. Therefore, if planting into cool soils with a history of seedling diseases, a fungicide seed treatment such as Acceleron® Seed Applied Solutions is recommended.
Soil Conditions. A number of soil conditions can affect soybean seed placement, germination, and emergence. Ideally, a well-drained soil is needed to enhance soybean yield. Loose, aerated soil increases water-holding capacity and allows air to reach roots for nitrogen-fixing to occur in the nodules. Cloddy, compacted, or crusted soils are some scenarios to watch out for when planting soybeans because they can result in reduced emergence. These factors are influenced by soil type, tillage practices, and weather. Under no-till or reduced tillage, most problems from planting occur when soil is too wet or too dry. When too wet, there is improper slot closure and firming; when too dry, it is difficult to get adequate coulter penetration and seed placement at the correct depth.
Soil Compaction. Soil compaction occurs when soil particles are pressed together to the point of reducing pore space and increasing soil density. Effects of compaction on soybean plants can appear as decreased seed germination, poor root and plant development, moisture and nutrient stresses, stunted plants, and ultimately reduction in yield potential. Poorly drained or compacted soils can also increase the potential of seedling diseases when planting in cool, wet conditions. Most soil compaction occurs due to equipment passes over a field. Research has shown that roughly 80% of compaction happens during the first pass with additional, but progressively less compaction in subsequent passes.3 The best way to manage compaction is through prevention. Planting or performing field work early when it is too wet can cause compaction and poor seed placement, which will likely outweigh the benefit of getting the seed in the ground early. If mud sticks to the tires and ruts are deeper than one inch, it is too wet to be in the field.
Soil Crusting. Lack of residue on fields with conventional tillage can result in crusting, which can lead to germination and emergence issues. Crusting is usually more noticeable in fields with a high silt content, low organic matter, and little surface residue (especially intensive tillage situations). Crusting can prevent emergence, reduce oxygen flow to roots, and create a barrier to water infiltration. If crusting is a problem, breaking up the crust with a rotary hoe is generally recommended to help expedite soybean emergence. Timing is critical for rotary hoe use to minimize damage to emerging seedlings.
Saturated or Flooded Soils. When soils are too wet, the result can be reduced emergence, plant population, and yield. Soybean plants need oxygen for productivity and saturated soils reduce the amount of oxygen available to the plant which results in reduced respiration. If you are planting into fields that have been subjected to flooding, it is important to remember that they are likely to be more susceptible to nitrogen and other plant nutrient deficiencies and some root rot diseases.
If flooding occurs on planted fields, the extent of flood damage to the crop will be related to water temperature, amount of water movement, duration of the flooding, and the growth stage of the crop during flooding. Soybean plants may tolerate 48 hours underwater, but 4-6 days can result in stand reduction, reduced vigor, and yield loss at around the V2 to V3 growth stage.4,5 When flooding occurs, higher temperatures are more detrimental, whereas cool, cloudy days with cool nights increases survivability. Flooding for 6 days or more at V2 to V3 growth stage may result in significant yield loss or entire crop loss.4,5
Seeding Depth. In order to help maximize soybean yield potential, planting should occur at uniform seed spacing and seeding depth. Seeds need good soil contact to ensure adequate moisture transfer to begin germination. Seeding depth should be 1 to 1.75 inches where tillage is used, and no deeper than 2 inches.1,2,6 When seeding under no-till conditions, a shallower depth of ¾ to 1 inch may be considered.1 Seeds should be placed shallower when planting earlier in moist soil conditions, or in heavy soils. Deeper planting depth should be used when planting later in dry soil conditions, or on light, well-drained soils. Furthermore, planting speed can affect seed placement, so drive no faster than the speed at which you can achieve uniform depth control within the range specified in the planter’s manual.
Row Spacing. Narrow rows can capture more sunlight energy and thus have the ability to produce more grain.1 The right row spacing for a situation can vary by soil type, planting date, weather, and product. Rows that are narrower than 30 inches, down to 15- or 20-inch rows, have a better yield response than 30-inch and wider rows.7 Drilled soybeans have the potential to perform better, but because the seed does not tend to be uniform in depth when drilling, any potential gains are usually offset by the inconsistent planting depth.7 One way farmers have been able to more efficiently use narrow row spacing is through the use of skip rows.1 A skip-row planting system uses narrow rows with strategically spaced wider rows to accommodate application equipment tires. This system is beneficial because of the ease of postemergence pesticide application with minimal crop damage while maintaining the yield benefit of using narrow rows.
In order to give a soybean crop the best opportunity for emergence and stand establishment, planting should occur when the soil temperature and conditions are favorable and seeds should be planted at the proper depth, seeding rate, and row configuration. Sometimes it means waiting for soils to warm up or dry out to help seedlings avoid diseases, reduced oxygen situations, and other unfavorable growing conditions. However, it is important to plant within the acceptable planting window for your geography in order to avoid late planting yield penalties.
1 Barker, D., Beuerlein, J., Dorrance, A., et al. 2005. Ohio Agronomy Guide 14th Edition. Bulletin 472. Ohio State University Exte http://extension.agron.iastate.edu.
2 2016. Soybean planting date can have a significant impact on yield. Iowa State University Soybean Extension and Research Program.
3 Daum, D.R. 1996. Soil compaction and conservation tillage. Penn State Cooperative Extension. http://extension.psu.edu.
4 Coulter, J., Naeve, S., Malvick, D., and Fernandez, F. 2014. Considerations for flooded corn and soybeans. University of Minnesota Extension. www.extension.umn.edu.
5 Sullivan, M., VanTooai, T., Fausey, N., Beuerlein, J., Parkinson, J., and Soboyejo, A. 2001. Evaluating on-farm flooding impacts on soybean. Crop Sci. 41:93-100.
6 Specht, J., Rees, J., Glewen, K., and Grassini, P. 2014. Soybean planting depth: Consider planting deeper. University of Nebraska-Lincoln Crop Watch. http://cropwatch.unl.edu.
7 Illinois soybean production guide. 2012. Illinois Soybean Association and Illinois State University Department of Agriculture. www.ilsoy.org.
Web sources verified 3/9/17.