By Melanie Barkley
As you travel to work this winter, you may notice somebody driving a tractor or 4-wheeler across a frozen pasture field. The farmer is spreading something across this field, and you wonder what he or she is doing. Likely, that person is making pasture improvements using a method called frost seeding. This method allows pasture improvements to take place at the end of winter when temperatures drop below freezing at night and rise above freezing during the day.
A key to any plant growing from a seed involves that seed touching the soil. Farmers call this seed to soil contact. During late winter, temperatures often drop below freezing. This causes the soil to freeze and look like the nooks and crannies of a honeycomb. Farmers spread seeds that land in the valleys of those honeycombs during early morning hours. Then, temperatures must rise above freezing that day so that the soil thaws and covers the seeds. Thus, frost seeding results in good seed to soil contact.
If you think back to last fall, that farmer allowed animals to closely graze that field or mowed them late in the season. Removing this extra vegetation helps to expose the soil so that the seed reaches the ground more easily. Fields with a thick layer of vegetation often do not frost seed well because the seeds do not reach the ground. The short plant height for the existing plants also reduces competition to the seedlings because the seedlings have better access to sunlight. Farmers will also mow or graze the field when plants grow to six to eight inches tall so that once again the sunlight reaches the new seedlings.
Not all plant seeds work well for frost seeding. Farmers who want to improve their pastures with this method mostly use seeds from legume plants. These plants have heavier seeds that settle better into the honeycombed soils. Legumes include plants such as alfalfa, red or white clover and birdsfoot trefoil. Research has demonstrated that red clover has the highest success rate with frost seeding.
Grass seeds traditionally do not work well for frost seeding. The seeds tend to be lighter in weight and may include a structure called an awn, which is a small stiff bristle on the end of a seed. These two factors often prevent the seed from becoming well covered by the soil once it thaws. However, farmers can overcome this problem by using a chain drag or lightly running over the field with a disc.
Why would a farmer want to frost seed a legume into a pasture? The answer is that legumes can help to “feed” the pasture grasses. Legume roots have nodules on them that take nitrogen from the air and “fix” them into the soil. This nitrogen is then available to feed other plants growing nearby. A pasture with 30% of the plants comprised of legumes and 60% of grasses makes a good combination to feed the animals and for the legumes to feed the grasses.
Another reason to frost seed a legume into a pasture is to thicken up a pasture stand. Over time, some plants begin to die out. This can be due to the age of the plant, insects, disease or overgrazing. Regardless of the reason, frost seeding can improve both forage quality and yield. This can then lead to faster growing animals, higher milk production, or even a greater likelihood for sheep or goats to produce twins.
Successful seedings always start with a soil test. Optimum fertility greatly increases the likelihood of seedling survival. Many farmers take soil samples in the fall so that if the soil pH needs adjusted, lime can be added to the field that same fall. Farmers take soil samples every three years to determine fertilizer rates to maintain optimum fertility in the soils. The soil test makes recommendations based on the type of crop growing in the field and the expected crop yield.
Frost seeding can be a very effective and economical method to improve pastures. It can improve both the quality and the quantity of forage produced in the pasture. Farmers who manage soil fertility and take steps to encourage good seed to soil contact can expect good results.