Alfalfa Seed Production

Historically, alfalfa seed production was centered in the Great Plains, where hay producers used old hay fields with thin stands. Between 1936 and 1945, Oklahoma ranked second in the United States in alfalfa seed production. Seed yields were 50-400 pounds per acre, and seed quality was frequently questionable. Recently, seed production has become specialized in the western states, where producers plant in wide rows with one to three pounds of seed per acre and obtain yields of 500-2000 pounds per acre of high-quality seed.

Despite the fact that seed production sometimes accounts for up to ten percent of the revenue from alfalfa in Oklahoma, it can best be considered a catch-as-catch-can operation for the majority of seed producers. Most alfalfa seed is produced in the western part of the state from fields that were originally sown for hay production but that now have declining  stands.

Alfalfa seed producers usually rely on wild bee pollinators exclusively or provide minimal numbers of honeybees. Only rarely do Oklahoma seed producers use alfalfa leafcutting bees or other contract pollination services. They usually harvest one or two cuttings of hay from a field, then let the next crop mature seed in August or September. Rainfall and soil moisture conditions in spring and early summer are major factors determining when alfalfa producers try for a seed crop. When moisture is limiting and the prospects for a good hay crop are poor at second or third harvest, alfalfa stands are allowed to mature seed. Thus the farmer exchanges two hay crops (with the accompanying labor and harvest costs) for one crop of seed. Even if seed yields are low (100 pounds per acre), farmers may make more money from seed than with two poor hay crops.

Alfalfa seed yields generally average from 150-200 pounds per acre statewide; however, individual yields of 500-1100 pounds per acre have been reported. After the seed crop is harvested, if there is adequate moisture, another hay crop may be harvested, or the stand may be grazed by cattle during the fall.

Generally, high rainfall seasons are not favorable for seed production in Oklahoma. For this reason, when moisture conditions are favorable for hay production, no seed crop will be harvested. This is why most producers consider it a catch-as-catch-can crop.

Alfalfa produces flowers over a period of approximately seven weeks. When a flower is pollinated, the seedpod develops and matures in 3-5 weeks. Under reasonably good conditions, each pod contains 3-5 seeds. Under conditions of high insect pest pressures, many pods do not contain a viable seed (see Chapter 2, "Insect Pests in Alfalfa Grown for Seed").

Most reliable alfalfa seed production in Oklahoma comes from stands harvested for hay about May 15 and left for seed until August. Seed are mature about four weeks after pollination, and it takes another three weeks for them to dry. If an alfalfa field blooms for three weeks, that's about 10 weeks from first bloom to seed harvest. To harvest seed in mid-August, alfalfa should be cut about May 15, as illustrated in Table 10-1.

Table 10-1. Reliable Seed Production Schedule for Western Oklahoma.

Cut for Hay	Grow Plants	1st Bloom	Blooming		Maturing		Drying	Harvest Seed
May 15		June 14		July 5		July 26		August 16

Seed fields normally have high populations of Lygus bugs, and controlling this insect may increase seed yields dramatically. Much of the flower drop in seed production fields is due to injury from Lygus bugs, but is most often blamed on dry weather. Early morning spraying for Lygus bugs when alfalfa first begins to bloom minimizes damage to pollinators. If honey bee hives are on trailers, they should be removed from the field for at least a day when spraying for Lygus bugs. In addition, seed producers should choose insecticides that are the least harmful to pollinators.

Windrowing Before Threshing: Alfalfa is usually cut and allowed to dry in the windrow before combining. This is an extremely vulnerable period for seed harvest. Hard rains accompanied by high winds can cause pods to pop open, allowing seeds to shatter or germinate in the windrow before threshing.

Seed fields should be swathed when about 60 percent of the seedpods have turned light to dark brown. Many pods that set late are still yellow at this time. Drying in the swath to about 14 percent moisture prepares the crop for combining. Do not crimp the crop during swathing.

Chemical Desiccation: When chemical desiccation of a standing seed crop is used, it can be ready for direct combining within three to four days after desiccation. Green pods do not ripen after desiccation, so nearly all the pods should be brown or yellow before applying the desiccant. Check the latest regulations and read the label before deciding to use a desiccant.

Regardless of how alfalfa is dried for seed harvest, clearance between the combine cylinder bar and concave should be 1/8-3/8 inch. Cylinder speed should be about 4000 feet per minute (850 RPM for an 18-inch diameter cylinder).

Specialized Seed Production: While most seed is produced in solid stands, research in Oklahoma has demonstrated low sowing rates (one to three pounds per acre) in 24-40-inch rows improves the reliability of alfalfa seed production. Under favorable weather conditions and correct management, fall-sown seedling stands can produce up to 500 pounds per acre the following August. In limited commercial production fields, this type of seed production practices has demonstrated that specialized seed fields may produce surprising forage yields, up to 2.5 tons per acre in late May and 1-2 tons per acre after the seed is harvested.

Alfalfa Production Guide for the Southern Great Plains, 2001
Comments and Questions:
E-mail: John Caddel

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