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SOYBEAN – SEEDING

For best results, follow the recommendations in this section on selecting a site, seeding management, residue management, and fertilization. For control of weeds, please seed Weed Control.

Seeding Equipment

Site Selection

PLAN AHEAD

  • Planning for soybean production should begin a year prior to planting.

Choose

  • Soybeans and other pulse crops are relatively intolerant to saline soil. Select fields with soluble salt levels <1.0 mmho/cm and avoid soybean production on fields with ≥2.0 mmho/cm.2.  Millimho per centimeter is the basic unit of measure of electrical conductivity in soil.
  • Choose fields with adequate amounts of iron (Fe) to meet the demands of soybeans. Some environmental conditions (excess moisture, salinity, carbonates and/or high nitrate levels in the soil) can reduce the availability and uptake of Fe by the soybean plant, leading to the condition known as Iron Deficiency Chlorosis (IDC).
  • Symptoms of IDC include yellowing of new soybean leaves between the veins (interveinal chlorosis), and an overall yellowing of soybean fields, particularly during the early vegetative stages in June. (Source: Manitoba Pulse and Soybean Growers)

Avoid

  • Avoid sandy, drought-prone soils.
  • Inadequate precipitation can reduce soybean yield due to this crop’s high water demand.
  • In heavy clay soils, soil compaction or crusting can reduce emergence.
  • Avoid rocky fields. Harvest operations are usually done close to the soil surface, and rocks can damage a combine.
  • Avoid poorly drained fields to reduce the incidence of seed and seedling diseases.

Maintain good records

  • Keep good records on herbicides used in previous crops – some leave residues that will injure the soybean crop. Always read the herbicide label and pay close attention to re-cropping restrictions.

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

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

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:

GROWTH STAGES

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.

 

Soybean Seed Quality Testing and Evaluation

GERMINATION TESTING

  • Germination testing is one method for evaluating seed lots for quality.
  • Germination addresses the seed’s ability to develop into a normal, healthy plant under favourable field conditions.
  • This testing can be misleading because seed may germinate well in the lab due to optimum conditions being present or to the fact that the seed has every opportunity to develop into a normal healthy seedling.

VIGOUR TESTING

  • Vigour testing, another method, assesses the seed’s potential to withstand unfavourable field conditions by assessing certain factors that influence seed quality.
  • While vigour results represent the lowest germination obtained from the lot, germination testing represents the highest result. Actual field germination would normally fall between the two.

VARIABLES IMPACTING SEED QUALITY

  • Germination and vigour are influenced by the physiological well-being and anatomical completeness of the seed plus its interaction with a wide range of environmental conditions.
  • Seed vigour is affected by:
    • genetic constitution
    • seed size and weight
    • mechanical integrity and soundness
    • deterioration, aging, and stage of maturity
    • pathogens
    • climatic conditions.

COMBINED TESTING

  • In years where unfavourable weather conditions prevail, it is best to combine a vigour test with a germination test to determine seed quality and performance more accurately.
  • Be sure germination results include adequate categorization of the seedling defects and the seedling’s ability to survive adverse conditions.
  • It’s impossible to predict post-seeding conditions with a vigour test, so seed is placed under a variety of stressful conditions, simulating climatic conditions as closely as possible, including:
    • cold temperatures
    • wet conditions
    • micro-organisms
    • seed soaking
    • accelerated aging.
  • Under these conditions, the seed must demonstrate the ability to germinate into a vigorous seedling.

Evaluation

  • Testing for vigour is an important tool if it is suspected that seed has sustained some injury or that the soil environment will impose stress on the seed.
  • Mechanical injury, such as small seed coat cracks, results in rapid water intake that leads to dead seed cells – this dead tissue then becomes a source of food for invading pathogens.
  • Vigour tests must be combined with germination tests to predict field performance.
  • The seed may also require 1000 seed weight and disease tests to completely assess the seed’s total quality.

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.