Source: Penn State University Extension
By Marvin Hall, Forage Production Specialist
Controlling the depth of forage seeding and ensuring good seed-to-soil contact are the keys to successful forage establishment in the summer.
More failures in establishing forages are the result of improper seeding depth than any other cause! If seeding depth isn’t correct then you might as well not bother to plant.
Forage seeds have a very small supply of stored energy to support the seedling until it emerges and begin making its own energy. Seeds placed too deep are not likely to emerge. Optimum seeding depth varies with soil type (sandy, clay, or loam), soil moisture, time of seeding, and firmness of seedbed, but generally is not more than 3/8 inch deep. A rule-of-thumb is that “5-10% of the forages seeds planted should be on the surface after seeding”.
Ensuring that seeds are placed at the proper depth requires a firm seedbed. It is extremely difficult to accurately regulate seeding depth if the soil is soft and fluffy. Here is a rule-of-thumb regarding soil firmness: On properly firmed soil, an adult’s footprint should not be deeper than ½ inch. Forage seeds should be covered with enough soil to provide moist conditions for germination but not so deep that the shoot cannot reach the surface.
Forage seeds need to absorb at least their own weight in water before germination begins. Unless the forage seed has been planted in saturated soils, the water generally moves into the seed from surrounding soil.
Adequate seed-to-soil contact ensures maximum water movement into the seed in the shortest time. Field situations (cloddy or loose soil) that do not promote good seed-to-soil contact generally result in extended germination periods and sporadic emergence.
The use of press wheels on a grain drill or culti-packing after seeding can improve seed-to-soil contact.