Clovers provide several benefits when they are used in pastures along with grass species. If the pasture species composition is 30 to 50% legumes research has showed us there is no benefit to adding additional nitrogen fertilizer. With current nitrogen prices in the 60 cents per pound range, the elimination of the need for commercial fertilizer can result in a savings of between $40 and $60 per acre per year based on nitrogen fertilizer recommendations for pastures and hayfields that are all grass.
Another benefit to having 30 to 50% of the pasture species legumes is that legumes will help fill in the "summer slump" that most cool season grasses have during the middle of summer. During this time frame legumes do not have the slowdow in growth that our common cool season grasses have. This provides growth that the animals can graze making for less acres or less need for supplemental feed for a given number of animals. A third benefit to including legumes in the pasture mix is that their presence increases the quality of the grazed feed because they are typically higher in nutritional value than grasses, particularly as the plants mature. This improved feed quality leads to better animal performance.
Ideally a farm would look at implementing a program where they would set up their pastures and permanent grass hayfields on a rotation where they would interseed 1/3 of them each year as the legumes should last at a sufficient level in the stand for three years.
A low cost method to get clovers into pastures is to frost seed this time of the year. Following are some considerations for pasture owners who may want to frost seed some clovers this spring.
Frost seeding is broadcasting forage seed on the ground surface while the ground is still frozen in the spring. Farmers have reported that frost seeding works 50 to 70 % of the time. Some feel it is worth it because of the cost saving from not needing a seeder. While frost seeding is a less expensive method of seeding forages than using seeders, it is also riskier than seeding with a drill because seed-soil contact is less good. Frost seeding can result in increased legume percentage but not in uniform stands of the seeded forage. Frost seeding may be acceptable for pasture improvement but not for establishing hay fields.
If a pasture has weed problems, get the weeds under control first. Herbicides used to control the broadleaf weeds will kill desirable legumes too.
The optimum is to seed early in the spring after the snow is gone but while the ground is still frozen. The principle is that freezing, thawing, and refreezing that occurs in the soil surface during this time will cause the seed to be incorporated to some degree into the soil to enhance germination. Frost seeding works best if pastures have been grazed short, about 2 inches in height, the previous fall to allow the seed to reach the soil surface.
Frost seeding on top of snow is not recommended because rapid snow melting may cause the seed to be washed off the pasture. Snow fall after broadcasting the seed will not hurt anything. Frost seeding should be done soon after the snow melts. Earlier seeding will also result in seed loss by birds, rodents, etc.
Frost seeding is not recommended for sandy soils because the freezing and thawing does not incorporate the seed.
Frost seeding works best for legume species that germinate rapidly, and at low temperatures. Legume seeding rates would be 2 to 4 lbs/a for red clover and white clover, once every three years. Red and white clovers are the easiest to establish but there has also been limited luck with birdsfoot trefoil. Frost seeding grasses is not recommended due to very low success rates. Some farmers broadcast a pound or two every year rather that higher rates every three years. Either way can be successful.
Legumes can also be interseeded using a no-till drill after the ground thaws, this may add a little more cost per acre, however success rate is generally also greater. Preparation of the field or pasture is the same, with a preference to having it short prior to drilling, and having weeds under control.
No-till drilling is the recommended way to add alfalfa to existing stands because alfalfa does not tolerate frost seeding well due having a higher germination temperature. Once the ground is thawed out and firmed up no-till drilling can take place. Pay particular attention to seeding depth. One quarter of an inch is all that is needed for the small seeded legumes, and seeding too deep will result in poor plant establishment.
Alfalfa is most likely the legume of choice for interseeding into grass fields that will be baled for hay because it is easier to get dry for baling.
In summary, there are a a couple different ways legumes can be interseeded into grass pastures and hayfields. Benefits from interseeding legumes include yield equal to a nitrogen fertilized cool season grass stand at a lower annual cost, growth of usable forage from the legumes during the cool season grass's summer slump time, and increase quality of the forages grown.