Soybeans are a crop that requires the full growing season to reach maturity. Early establishment and emergence in the spring are key to ensuring a successful soybean crop.
Time of Seeding
Before diving into soybean establishment, “when to seed?” becomes the first question to answer. Soybean days till emergence will vary greatly based on soil temperatures, so placing into soils warmer than 10°C is ideal. Seeds take in water within the first 12-24 hours in the ground and you’re looking for this first moisture in the seed to be warm and avoid shocking the seed. Seeding with a forecast of warm, sunny conditions will increase the chances of emergence and minimize the risk of injury. Depending on the year, these soil and weather conditions are not typically seen until mid May.
Research from the University of Manitoba found that soybean yield was similar when seeded from April 28 to May 24, but the early seeding date of April 28 did expose plants to frost damage. Seeding into June lowers yield potential, as soybeans require 105-125 frost-free days from planting to maturity. A good rule of thumb is to seed soybean within two weeks of the last expected spring frost in your area.
“Growers have to assess frost-risk and balance seeding operations based on other crops’ needs,” says Rene Mabon, Agronomic and Regulatory Services Manager with BrettYoung.
Narrow or wide rows both have their advantages when it comes to planting soybeans. Narrow rows of less than 15 inches offer faster canopy closure, which can help with moisture retention and weed control, whereas wider row spacing allows airflow throughout the canopy to minimize disease pressure in wet years. Row spacing is taken into consideration when determining seeding rates and target plant densities.
Mabon says, “Like in canola, plant populations matter in soybean too. Make sure you are seeding to a target population and adjusting up or down based on conditions.”
The optimal plant density for soybean is 140,000 – 160,000 plants per acre. Seed survival, row spacing and other risks need to be factored in when determining a seeding rating. Manitoba Pulse and Soybean Growers (MPSG) offer a Soybean Seeding Rate Calculator to help make these calculations.
Optimal seeding depth for soybean is 0.5 – 1.5 inches, into a warm, moist seedbed. On dry years, it’s best to avoid chasing moisture with seeding depth and wait for a timely rain to allow for uniform emergence. A packed, firm seed bed will allow for increased seed to soil moisture contact.
If land rolling, look to make this pass immediately after seeding or wait until post-emergence at the first trifoliate stage, to minimize plant damage. Soybean rolling creates a smoother and firmer seedbed, and many benefits are seen at harvest including reduced risk of equipment damage, faster and easier harvest, and cleaner seed.
Nutrient applications during soybean seeding are usually minimal due to the plant’s ability to fix nitrogen and to extract phosphorus (soil test range of 10 – 20 ppm) and potassium (more than 100ppm) from the soil. Soils usually receive enough fertilizer from other crops in rotation to provide sufficient levels for soybeans. Soil nutrient analysis is the only way to determine if an application is warranted.
“Nodulation is critical to a successful soybean crop. Inoculation decisions are as important as variety, fertility and weed control decisions when planning a soybean crop,” Thomas Thiessen, Soybeans, Corn, and Ag Biologicals Product Manager with BrettYoung.
Inoculation of soybeans with Bradyrhizobium japonicum bacteria help root nodules form and nitrogen fixation to occur. Inoculants are available in many forms which allow for the products to be placed on the seed and/or in-furrow. Double inoculation should occur for fields with no recent history of soybeans, whereas single inoculation will get the job done on fields where soybeans are well established in the crop rotation. It’s best to evaluate nodulation at early flowering, where at least 10 healthy nodules should be found per plant.
Yield success starts in the spring with uniform plant establishment.
For more information on soybeans, contact your BrettYoung Regional Account Manager.