Numerous benefits are associated with adding legumes to established tame stands. Some of these benefits include nitrogen (N) fixation with establishment to reduce N needs by grasses, strengthen the grazing system for livestock, and tend to increase palatability and forage quality compared to monoculture grass stands. Adding legumes to tall fescue can reduce fescue toxicosis. Adding another species to an established grass stand may sound complicated, but it can often be beneficial for the entire forage system in the long run when the correct steps are taken.
What is frost seeding?
No-till seeding, minimum tillage, and frost seeding are all techniques used to introduce or reintroduce clovers into grass stands. Frost-seeding, as the name suggests, requires minimal equipment and is among the simplest options. Frost-seeding is accomplished by broadcasting legume seed onto the existing field of grass from late winter into early spring and allowing freeze-thaw cycles to incorporate the seeds into the soil. For most of Kansas, this would be the mid-February through mid-March time frame, accounting for the temperature gradient across the state. Due to seed costs, this practice should be done with favorable establishment moisture, limited insect populations, and short pasture/forage stubble to minimize grass competition.
The longevity of legumes in a stand depends on establishment success, soil fertility, grazing/haying pressure, and grass and weed competition. Research from other universities has noted two to four years as an average, while some stands last for far longer, and others never establish.
Choosing a legume for frost seeding
Overall, the most successful species for frost seeding are crimson, red, and white/ladino clovers. Birdsfoot trefoil, chicory, annual, and Korean lespedeza have mixed results with this practice and often have limitations in seed availability and stand longevity, making the investment potentially less favorable. This practice is not recommended for alfalfa.
Factors to consider when frost-seeding a legume
Soil fertility: Clovers need a pH of 6.5 to 7, and adequate levels of plant-available P and K. Overapplication of N will support grass production. Soil sampling is critical.
Variety: If available, choosing a known variety (not VNS “variety not stated”) with known performance and genetics will increase hay tonnage, improve forage quality, and improve stand life.
Seed treatment: Make sure the seed has been inoculated with the correct rhizobia, especially in fields that have not had the legume you are planting in recent history. Remember that a standard soybean inoculum will not work for clovers.
Seed per square foot: Make sure there is enough seed being broadcast with seeding rates of 6 to 8 pounds for crimson and red clover and 3 to 4 pounds per acre for white/ladino clover. If mixing the red and white clover when seeding, apply the minimum seeding rate of red clover (6 lb./A) mixed with 1 lb./A of white/ladino clover.
Seed-to-soil contact: Seed needs to land on bare soil and be worked into the top ¼ inch by rain, snow, and/or freeze-thawing. When broadcasting, the driving factor behind frost-seeding failure is too much forage ground cover, so the current forage height needs to be considered. A corrugated roller can be used to push seed into the soil, while livestock traffic or dragging a chain harrow can ensure seeds fall through the grass thatch later if excessive.
Weed management: Until clovers are well established, many broadleaf herbicides will kill out the clover. This means weed control should be done before establishing covers. Once clovers are well established, some herbicide products for broadleaf control are considered clover safe. Always check the herbicide label before an application.
Tina Sullivan, Northeast Area Agronomist
tsullivan@ksu.edu
Logan Simon, Southwest Area Agronomist
lsimon@ksu.edu