Benefits of Frost Seeding Legumes

– Curt Stivison, Fairfield County Soil and Water Engineering Technician

Adding legumes to hay and pasture fields brings at least four benefits and frost seeding is a simple, but effective method. Broadcasting legume seed on the soil surface as it ‘honeycombs’ in late winter (February 15 to March 15) allows the seeds to become covered as the soil freezes and thaws.

1) Higher yields: The total yield of forage per acre is increased. For example, a study conducted at Lexington, Kentucky compared renovating a fescue pasture using red clover to fertilizing the grass with nitrogen. In this study, adding 6 pounds of red clover seed to a fescue pasture produced higher yields than fescue fertilized with up to 180 lb N/ac.

2) Improved quality: Adding legumes to grass fields improves forage quality over grass alone. This added quality includes increases in palatability, intake, digestibility, and nutrient content. The result is improved animal performance. Research has shown that legumes improve animal growth rates, reproductive efficiency, and milk production.

3) Nitrogen fixation: Legumes get their nitrogen needs from symbiotic bacteria that live in “knots” (nodules) on their roots. These bacteria are added when the legume seed is inoculated. This “fixed” nitrogen provides the nitrogen needed by the legumes and also grasses growing with them. Alfalfa usually fixes the most, between 200 and 300 pounds/acre/year, while annual lespedeza is on the low side with about 75 pounds. Red clovers can fix 100 to 200 pounds of nitrogen/acre/year. With nitrogen cost at 56 cents a pound that equals 56 to 112 dollars an acre benefit in nitrogen alone. At the recommended seeding rates of 6 to 12 pounds (depending on conditions) and a cost of $3.25 a pound, that equals 20 to 40 dollars per acre.

4) More summer growth: Most of the growth of cool-season grasses occurs during the spring and fall. Legumes make more growth during the summer months than cool-season grasses. Growing grasses and legumes together improves the seasonal distribution of forages and provides more growth during summer.

Controlling grass and weed competition in a new seeding is critical. Many attempts at renovation have failed simply because grass was allowed to grow and reduce the light, nutrients, and water available to the young legume plants. The grass must be kept short by grazing or mowing until the new legume plants are 3 to 4 inches tall. Stop grazing if the animals begin biting off the young legume leaves. Grazing and mowing should be stopped for several weeks to allow the legumes to become well established. After this, the field should be mowed or grazed on a schedule that will help keep the particular legumes used in good condition. A rotational grazing system helps keep legumes in the stand longer.

Find more details about frost seeding forages in OSU Extension Fact Sheet “Improving Pasture With Frost Seeding