Sow legumes in winter for cheap fertilizer in spring pastures

With nitrogen prices high, Craig Roberts says this winter, it’s important to consider freeze-seeded legumes as an alternative fertilizer source.

“2022 is different because fertilizer costs have tripled,” says the state forage specialist at the University of Missouri Extension. “Think of legumes as almost free fertilizer.”

Frost seeding, a method of broadcasting seeds to frozen pastures, improves poor pastures at low cost, Roberts says. The seeds penetrate the ground and germinate when the ground freezes and thaws.

Gel seeding requires less fuel, labor and equipment than other methods, Roberts says. It works in an age where heavy equipment could rut and compact wet fields.

More importantly, nitrogen-fixed legumes can be another option for fertilizer.

Legumes fix nitrogen. The root nodules of legumes fix nitrogen from the air. Not all legumes are created equal when it comes to nitrogen fixation, Roberts says. In a typical year, fixed nitrogen replaces 25 to 75 pounds per acre of fertilizer.

Red clover, white clover and annual lespedeza are the three main legumes recommended for frost seeding in Missouri, Roberts says. Other legumes include alfalfa, birdsfoot trefoil, hairy vetch and sunn hemp. These should be sown later in the year.

When to sow on frost in Missouri

Roberts says frost seeding is easy for clover and annual lespedeza. Most growers use a hand-held whirlybird or a whirlybird attached to a four-wheeled vehicle.

There are several advantages to doing this on snow, Roberts says. It is easy to see where the seeds have been scattered and there is less risk of rutting or compaction of wet soils since the ground is frozen.

Throughout most of Missouri, released in mid-February when there is snow or severe frost. Frozen seed in late January in southern regions or late February in northern counties.

Roberts specifically recommends not frost seeding alfalfa and bird’s eye clover in January or February. If sown, the seed may germinate and emerge before an ice storm. Roberts says he doesn’t recommend interplanting birdsfoot trefoil because it has low seedling vigor in Missouri.

The seeds must come into contact with the soil

Seeds need the action of freezing and thawing for good soil contact and to pull the seed to the top soil layer, Roberts says.

The best contact occurs on exposed ground. Plant residues can prevent seeds from reaching the ground. The sabotaging action of cattle can help drive the seeds into the soil.

Apply little or no nitrogen in the spring

Legume seedlings need time to grow without competition for light and nutrients from grass canopies, so apply little or no nitrogen in the spring. Adding more nitrogen fertilizer decreases the amount and size of nodules.

Wait until fall when root systems are strong. Graze or prune frost seeded pastures in the spring and summer to allow light to reach the seedlings.

A four-year study by UM researchers, titled “Nitrogen Fertilization Rates Influence Stockpiled Tall Fescue Forage Through Winter,” shows that nitrogen increases grass competition and significantly blocks light penetration into the Red clover.

Seeding rates vary depending on the legume. Roberts recommends the MU Extension publication “Seeding Rates, Dates, and Depths for Missouri Common Forages” on extension.missouri.edu to determine seeding rates.

Craig Roberts, forage specialist at the University of Missouri Extension, describes the benefits of legumes for farms:

Legumes improve digestibility. Grazing cows love legumes. Pulses improve digestibility with higher crude protein content and higher mineral content, especially calcium and magnesium.

Animal performance improves with legumes. Studies show that animal performance and weight gain improve with legumes, especially clover.

Legumes extend the grazing season. Legumes grow best in late spring and summer when the fescue grows slowly or not at all. Cool-season grasses get two-thirds of their growth in the spring and one-third in the fall. The annual lespedeza fills this gap, known as the “summer crisis”.

Legumes contribute to animal health. Adding red clover to fields of common tall fescue helps prevent some animal health issues, Roberts says. Adding legumes dilutes fescue toxicosis. More than 90% of Missouri fields contain toxic Kentucky 31 tall fescue.

Fescue toxicosis causes vasoconstriction, a narrowing of blood vessels. In summer, this causes heat to build up in an animal’s core body. In winter, the blood does not flow to the extremities, and the hooves fall off. Red clover contains compounds that open blood flow, reducing vasoconstriction.

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