Is there an ideal planting depth for soybeans?

March 16, 2021

The issue of seed planting depth comes up every year with different information circulating in the industry. But does the depth at which you plant soybean seeds actually affect the yield? 

Absolutely! Naturally, seed depth is important, especially since soybean seeds are more sensitive when sown too deeply. This is why it’s important to make sure you have the right information so you can start your crop off on the right foot. Planting the seeds at the right depth will produce more even crops with a higher yield. If planted too deep, they will struggle to emerge. They will also be more vulnerable to diseases and insects like seedcorn maggot, especially since growers are planting earlier and earlier in the season, increasing the number of days before emergence. If planted too close to the soil surface, germination may be delayed from lack of moisture.

Depending on the soil type and soil and the conditions, a seed depth of 3.8 cm, or 1.5”, is appropriate for soybeans. For directly no-till seeded crops, the seed depth can often be reduced to 2.5 cm, or 1″, if there is adequate moisture in the ground. A soybean seed needs to have 50% of its weight in water to begin germination. Whenever possible, plant the soybeans at a depth of 1 cm (1/2”) in damp soil, and never more than 6.4 cm (2.5”) deep, as newly planted soybean seeds fully depend on their energy reserves to push through the soil and will not be able to reach the surface if planted too deeply. It’s also worth noting that varieties with larger seeds contain more energy, meaning they can better handle deeper planting. 

It is difficult to plant seeds at an exact depth with certain seeders, especially for directly no-till seeded crops, which is why it’s important to check the depth in each field. The soil type may affect the depth of the seeds, despite the same setting being used on the seeder. It is also important to be sure you have good seed-to-soil contact and have properly adjusted the wheels to close the seed slot. 

In general, the key to success is planting in a fine seedbed with a correctly adjusted seeder. Some varieties are able to emerge from the ground after being planted more than 5 cm (2″) deep, but we shouldn’t generalize, especially in cold spring conditions! 

Once we’ve established the seed depth, when is a good time to start planting? Some important indicators to look for:

  • Plant when the soil temperature reaches 10-13°C (over 50 °F) where the seeds will be planted.
  • The seeds should be planted between 2.5 cm and 3.8 cm (1″ and 1.5”) deep in soil when the ambient temperature will continue to rise in the days following planting. 
  • The first 24 to 48 hours are important for the soybean’s germination and yield potential.
  • It’s also recommended that you roll/pack the soil after seeding to conserve soil moisture.

Some growers plant very early in the season, but be careful! For those who usually take advantage of these early windows, it is important to consider fungicide seed treatments to protect the seeds from diseases like pythium and phytophthora. Soybeans are somewhat tolerant to spring frosts as cold as -2.8 °C (30 °F) for short periods of time, but it is strongly recommended that you avoid this situation to prevent crop losses and maximize the variety’s potential yield. 

Happy planting season!