Get “almost free” fertilizer by sowing legumes on frost

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COLUMBIA, Mo.—High nitrogen prices make it especially important to consider frost seeding legumes this winter, said University of Missouri State Forage Specialist Craig Roberts. Extension.

“2022 is different because fertilizer costs have tripled,” Roberts said. “Think of legumes as almost free fertilizer.”

Frost seeding, a method of spreading seeds on frozen pastures, improves poor pastures at low cost, he said. 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 said. It works in an age where heavy equipment could rut and compact wet fields.

More importantly, nitrogen-fixed legumes can be an alternative to fertilizers.



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

BENEFITS OF LEGUMES

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

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

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

Legumes extend the grazing season by growing 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”.

There are also veterinary benefits. Adding red clover to fields of common tall fescue helps prevent some animal health issues, Roberts said. 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

WHEN TO FREEZE SEEDS IN MISSOURI

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

There are several advantages to doing this on snow, Roberts said. It’s easy to see where the seeds have been scattered and there’s less chance 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. Frost seedlings in late January in southern regions or late February in northern counties.

Roberts specifically recommends no frost seeding of alfalfa and birdsfoot trefoil in January or February. If sown, the seed may germinate and emerge before an ice storm. Roberts said he doesn’t recommend intercropping bird’s-foot trefoil because it has low seedling vigor in Missouri.

Seeds need the freeze and thaw action for good soil contact and to pull the seed to the top soil layer, Roberts said.

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

APPLY LITTLE OR NO NITROGEN 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. Read the full report at acsess.onlinelibrary.wiley.com/doi/abs/10.2135/cropsci2016.02.0097.

Roberts recommends the MU Extension publication “Seeding Rates, Dates, and Depths for Missouri Common Forages” at extension.missouri.edu/p/G4652 to determine seeding rates.

For more information, see “Seeding Legumes in Pastures Can Offset High Nitrogen Prices” in MU’s Integrated Pest and Crop Management Information Bulletin, or watch a video of the town hall on MU livestock and fodder at youtu.be/zkYQo251xDQ.

Roberts also recommends pasture renewal workshops from the Alliance for Grassland Renewal. See GrasslandRenewal.org/workshops.

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