Forage seeds, being small, don’t come equipped with a large supply of stored energy to carry them through the initial establishment phase prior to leaf development. Seeds that are placed too deep simply run out of fuel before they can emerge.
In Penn State’s Field Crop News, Hall points out that optimum seeding depth varies with soil type, soil moisture, time of seeding, and firmness of the seedbed; however, this depth is generally not more than three-eighths of an inch. “A rule of thumb is that 5 to 10 percent of the seeds should be on the surface after seeding,” says Hall.
A firm seedbed is the key to proper and consistent depth placement. This often requires rolling or cultipacking fields before seed placement in the soil. A follow-up firming helps to ensure good seed-to-soil contact.
“Once placed into the soil, the seed needs to absorb its weight in water,” explains Hall. This process is most efficient when the seed is tightly surrounded by soil. Field conditions such as cloddy or loose soil contribute to a poor seed-to-soil interface. A firm seedbed also helps to conserve moisture below the surface during dry conditions following seeding.