Cover crop seed application is as important as commercial seed application and the method used will effect seed germination rate and stand quality. Using equipment that allows accurate application at the correct rate will save money and help ensure sufficient cover. Since cover crop seed sizes and weights vary, it is important to match equipment to both the seed and management practice.
Start by choosing a cover crop and a method for its application (see specific cover crop information sheets for recommendations). Some methods and equipment might include:
Broadcasting by air: Cover crops can be applied from a broadcast seeder mounted on an airplane. This practice works well for larger seeds like rye and wheat, but is not recommended for small clover or grass seeds. Broadcasting by air allows for the overseeding of an existing crop or for planting when soils are too wet for ground seeding, although seed germination might be slower and a higher seeding rate may be needed.
Broadcasting by ground: This is the most popular and accurate seeding method and may be done using spinners, drop tubes or air pressure. The most critical factor is accurately metering seed before it is spread. Make sure the seeding pattern is appropriate for complete and even ground cover. Different seeds have varying spread patterns based on their respective weights, and heavier seeds spread further than lighter seeds. This can cause difficulties when heavier and lighter seed mixtures are applied. Broadcast seeders may be mounted on ATV's, tractors, tillage tools or other implements.
Incorporation: Cover crop seeds produce better stands with shallow soil incorporation. Excellent results can be obtained by combining broadcast seeding with a cultivator or other incorporating tillage tool. The combination chosen depends on when seeding takes place and what management practices are in effect. Most cover crop seeds are very small and do not need much soil cover, just good seed-to-soil contact.
Drilling: This is another good cover crop establishment method, as most drills are equipped with a legume/grass seed box. Drilling works well for metering small seeds (use the standard drill box for larger seeds) and gives good placement and seed-to-soil contact. Drilling can be especially successful in no-till management systems.
There are many variations on these methods. Watch different equipment in action on farms and at farm shows. Every piece of equipment is different, and individual farm needs depend on the management system in use.
Here are a few helpful hints:
- No matter what seeding equipment is used, an agitator in the seed box is essential when using grass seeds. The agitator prevents bridging and keeps seeds flowing uniformly.
- A slower-turning metering unit and a larger feedout opening reduce seed grinding and cracking.
Accurate seeding equipment calibration is essential for applying cover crop seeds. Calibrate a seeder each time a different type of seed is used and routinely during the season. Use the following steps as a guide to calibrating a broadcast seeder:
- Determine the desired application rate (in pounds per acre).
- Fill the seeder.
- Determine the spread width. The spread width will be smaller than the actual width the seeds are spread. Allow for enough overlap so a consistent pattern is achieved.
- Set the seeder opening on the desired setting.
- Catch the seed being applied for one minute. Be sure to stay away from all moving parts.
- Determine the area that would have been seeded (if actually moving) using the following formula: length (in feet) of area seeded (tractor speed converted to distance traveled in one minute X spread width (in feet) ÷ 43,560 = acres seeded).
- Divide the volume collected (in pounds) by the area seeded to obtain the actual seeder output in pounds per acre.
- Make adjustments to tractor speed and/or seeder setting and repeat steps 5-7 to change application rate to the desired value.
Frost-seeding: Seeding a cover crop into an established crop in late winter to very early spring. Example: Seeding red clover into wheat in March.
Interseeding: To prolong the cover crop growing season it is sometimes possible to plant a cover crop into the growing cash crop. Careful consideration needs to be made regarding the stage of the cash crop, cover crop species selection, and environmental conditions. Consult an experienced cover crop user to prevent issues such as cash crop yield loss (due to competition), reduced harvest efficiency, and failed cover crop establishment (due to reduced light penetration through the cash crop canopy and moisture stress). Examples: crimson clover seeded into corn at the V6 corn stage and annual ryegrass flown onto seed corn in late August in south-west Michigan.
Pre- or Post-season seeding: Cover crops can be planted early in the growing season before late-season vegetables or field crops (e.g. dry bean) or after cash crop harvest. Example: Cereal rye following potato harvest.