SOYBEAN SEED MANAGEMENT

SEED

• Use seed with both high germination and vigour.

SEEDING DATES

• Soybeans are very sensitive to cold water uptake immediately after planting.
• Planting date is determined to a large degree by soil temperature. Ideal soil temperatures will be at least 10°C at seeding depth.
• Seeding below these temperatures may delay emergence and may result in reduced stand establishment.
• The first water that the soybean absorbs in the hours after it is seeded is important to be warm to avoid seed chilling.
• Seeding fields later in the morning, when soils have warmed up a bit more from overnight and will continue to warm throughout the day, and avoiding seeding if a large rain is forecast, will help reduce the uptake of cold water.
• Seeding as early as soil temperatures permit is important as later seeding dates can result in decreased plant height and lower pod establishment, making harvest difficult.
• Later seeding also increases the susceptibility to fall frost and reduces seed yield potential.
• May 10 to the 25 is a typical seeding window of soybeans. Research is currently being done to evaluate ideal seeding dates across the Prairies.
• Once soybeans emerge, they can tolerate light frosts of up to -2°C for short periods, as long as the growing points are not damaged.

SEEDING DEPTH

• Soybeans are a relatively large seed and require adequate moisture to hydrate and germinate. They need to be able to remain in contact with moist soil.
• Ideal seeding depths range from 0.75 to 1.5 in (1.9 to 3.81 centimetres). Deep-seeding can reduce emergence and increase the risk of disease infection from soil-borne pathogens.

SEEDING RATE CALCULATOR

• A Seeding Rate Calculator to help you determine the proper seeding rate will soon be available on the Alberta Pulse Growers’ app. Download the app here to be notified of when the calculator becomes available.

Seeding Rates

• Soybean seeding rates should be determined by targeting desired final plant stands. Using this method, you need to take into account the desired plant population, the variety seed size (thousand kernel weight), and the percentage seed survival. Soybean seeding rates are usually given in seeds per acre (plants/ac).
• Ideal final plant population ranges four to five plants per square foot. Average seed survivability of around 75% is usually achieved when using a drill.
• A planter is typically able to achieve a higher seed survivability rate. Overall, seed survivability will depend on equipment, seed quality, and seedbed conditions. This means seeding rates will range from 70 to 140 pounds per acre (lb/ac), depending on the various factors.
• Exceeding ideal plant stands can result in drought stress during dry years and lodging in wet years. Soybeans can branch to help compensate for lower plant stands but plant height and pod height are usually lower with a less dense stand, creating more issues with harvestability.

Seeds Per Pounds

• 2,000 – 3,400 seeds per pound

SOIL TEMPERATURE

• Ideal soil temperatures will be at least 10°C at seeding depth.
• Soybeans emerge within 24–35 days when seeded into 6–12°C soils and 4–16 days when seeded into 14–22°C soils (based on soil temperatures at a 5 cm depth at 10:00 a.m. for two consecutive days). (Research conducted at University of Manitoba)
• Warm soil temperatures result in faster emergence and prevent the risk of chilling injury during inbibition. Residue management should have a minor impact on plant population and yield if soybeans are seeded during optimal calendar dates and into warm soil.

Other Considerations

TYPE OF EQUIPMENT

• Soybeans can be seeded using conventional air drills and air seeders found on most farms. They can also be seeded as row crop with planters on row spacings ranging from 15 to 30 inches (in).
• Research in Manitoba and North Dakota has found that narrow-row spacings typically yield the same or higher than wide-row spacings.
• Narrow rows will require a slightly higher seeding rate compared to a planter, to compensate for less concentrated rows and potential seed damage, especially when seed is less than 12% moisture. However, narrower rows will achieve canopy closure more quickly, helping with weed competition and moisture conservation.

PACKING

• Packing to improve seed-to-soil contact is important – but don’t overdo it, especially in heavy, wet clays (this can be especially detrimental if air temperatures rise quickly and the soil bakes and crusts).

LAND ROLLING

• Soybeans are harvested very low to the ground, so rolling should be done if possible.
• Soybeans are sensitive to rolling once they have begun to break the soil surface. Soil compaction at this time can break off fragile emerging soybeans which kills them, so it is important to get out and roll the field within a few days of seeding.
• If you miss the window prior to emergence, wait until soybeans are at the first trifoliate stage and it is a warm, sunny day, so plants are wilty and less likely to break. It is much better to roll when they are not emerged.
• Care should also be taken to avoid rolling when soil is wet. Compaction and soil crusting can inhibit seedling emergence, especially in heavier textured clay soils.

Resources:

• Government of Alberta Land Rolling Guidelines for Pulse Crops in Western Canada
• Tips for Rolling your Pulse and Soybean Crops

GROWTH STAGES

• To understand the growth stages of the soybean – refer to the Soybean Plant Development Guide.

SEED TREATMENTS

• Soybeans are susceptible to a number of early season seed and seedling diseases, and some soil insects. Fungicide and insecticide seed treatments are available and should be assessed on a field-by-field basis.

Residue Management

FALL PRIOR

• Use proper straw and chaff management in the fall before seeding a soybean crop is critical.
• Heavy straw conditions can create seeding problems such as hair pinning with disc openers or plugging between the shanks of an air seeder.
• Hair pinning refers to a condition where the seed is pushed down onto the straw layer by the opener, creating a wicking effect, where there is poor seed-to-soil contact and, as a result, patchy or poor germination of the soybean crop.
• Thick layers of chaff may also cause phytotoxicity to the next crop. 
• Phytotoxicity is the phenomenon of reduced growth and yields of the next year’s crop due to toxic compounds leached from the residue and/or microbial activity that produces toxic compounds during breakdown of the residue.

Direct Seeding Considerations

• Direct seeding is usually defined as seeding into standing stubble, but can also be referred to as reduced tillage.
• Even and wide distribution of residue with a durable straw chopper and chaff spreader is vital.
• To avoid plugging shanks, stubble height should be the same or less than the shank spacing of the seeding tool.

ROTATIONAL PLANNING

• Proper rotational planning can also assist in managing heavy residue:
  • avoid planting high-residue crops back-to-back
  • include forages in the crop rotation
  • periodically bale and remove straw.