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Alfalfa (Medicago sativa L.), also called lucerne, originated near Iran, but related forms and species are found as wild plants scattered over central Asia and into Siberia. Its value as feed for horses and other animals was described as early as 490 B.C. by Roman writers. Alfalfa was first introduced into the eastern US by the colonists in 1736.
Called the “Queen of Forages”, alfalfa is not only the oldest cultivated forage crop in the US, but it is one of the most palatable and nutritious. Alfalfa is rich in protein, vitamins, and minerals. And, when cut prior to bloom, it is low in fiber and high in energy. Thus, it is prized as a primary component in dairy cattle rations and is an important feed for horses, beef cattle, sheep, and milking goats.
Alfalfa has a very high yield potential compared with that of other forage crops. It also is an integral component of many crop rotations because of its ability to fix nitrogen, improve soil structure and tilth, and control weeds in subsequent crops.
Alfalfa is a herbaceous (definition link) perennial legume. A mature alfalfa plant may have from 5 to 25 stems, which usually reach a height of 15-25 inches (38-63 cm). Stems are branched and slender and bear pinnately trifoliolate leaves. Leaves with more than three leaflets are not uncommon (picture link). Leaves are arranged alternately on the stem Stipules are slender and adnate (fused) to the petiole (picture link). Leaflets are linear, oblong, or obovate oblong and are toothed toward their apices (picture link).
Area of Adaptation
Alfalfa is worldwide in its distribution (world crop and statistical table link) and is grown in many areas of the US, accounting for nearly 30 million acres (12 million ha) of production. A wide range of soil and climatic conditions are suitable for alfalfa, but for best production it requires a well-drained soil with nearly neutral pH and good fertility. Alfalfa should not be expected to do well in poorly drained or acid soil or in areas where adequate water is not available.
Alfalfa is used primarily as a hay crop. It has the highest feeding value (section link) of all commonly grown hay crops when harvested at late bud or early flower stage of maturity (table link). Alfalfa produces the greatest amount of protein per acre of any livestock feed. It is often used in combination with corn silage in livestock rations to take advantage of the protein and energy content of the two feeds. Alfalfa also can be made into silage, pellets, meal, or cubes. With careful management, alfalfa can be used successfully as a pasture crop.
Early season grazing of alfalfa provides a method of using the first cutting, which often is damaged by spring rains if made into hay. When pastures are grazed, however, the soil must be dry enough to avoid crown damage from trampling.
If alfalfa is used for year-round pasture, a rotational grazing system must be provided to allow root reserves to be replenished. A rotation that provides 30 to 35 days of regrowth is adequate. If continuously grazed, plants should be kept between 3 and 6 inches (8-10 cm) tall during the spring and summer and allowed to increase to a height of 8 to 12 inches (20-30 cm) during the fall. This top growth may be removed following a killing frost without reducing winter survival.
Bloat (fact sheet link) often is a problem for animals on pastured alfalfa. Unfortunately, the methods of controlling bloat often have been troublesome, expensive, and only partially effective. Using a grass-legume mixture in pastures, supplementing legumes with grass hays, intensive strip grazing (section link) with electric fences (section link), and drylot feeding have all been somewhat successful.
The most promising preventative treatment involves the use of bloat-preventative materials (table link). These anti-foaming compounds may be added to drinking water, applied as a top-dressing on grain supplements, included in pellets, or added to salt-molasses blocks supplied on pasture. However, the effectiveness of these methods is variable and depends upon animals obtaining a regular supply of bloat preventative.
Many cultivars (cultivated varieties) of alfalfa are available with specific characteristics for climatic, soil-related, insect, and disease problems. Dormant, moderately dormant, and non-dormant cultivars are available for the different climatic regions. Consult your county agent, consultant, or seed dealer for cultivars that will do well in your area (cultivar selection program link, CASC link, GRIN link)).
Alfalfa requires a deep, permeable soil with an adequate moisture supply during the growing season for maximum yields. It is very sensitive to poor drainage and compacted soil conditions that restrict root growth. Thus, alfalfa is most productive on loam or loamy soils that are both well drained and have good moisture-holding capacity. Alfalfa does not tolerate acid soils (section link) (pH below 6.2), especially in the seedling stage.
A good seedbed for alfalfa is finely pulverized, leveled, and firmed to the seedling depth and contains soil moisture near the surface to initiate germination. Leveling the field to eliminate low spots will result in a more uniform stand and ease equipment travel for the life of the stand.
Most alfalfa seeding in the US occurs either in the early spring or in late summer and fall. Time of alfalfa seeding is influenced by precipitation patterns, temperature, and cropping patterns. Spring seedings allow for harvest during the seeding year, but weed control usually is required. Late summer and fall seedings usually avoid weed competition and unfavorable summer temperatures and moisture conditions but must allow for adequate seedling development prior to the onset of winter.
Spring seeding should be made early enough to allow good root systems to form before high temperature and low moisture conditions slow growth rates (seeding date program link). Late summer and fall seedings must be made early and have sufficient soil moisture to allow enough growth to minimize loss of stand from winter injury.
Alfalfa seed must be placed in contact with moist soil. Seedlings are unable to emerge from the soil if planted too deep. For best seedling survival, drill seeds approximately ¼ inch (0.6 cm) deep. Seedling emergence is greatly reduced when seeds are planted deeper than ½ inch (1.3 cm).
A seeding rate of 12-15 lb/a (13-17 kg/ha) planted in 6 inch (15 cm) rows usually is sufficient for a good stand of alfalfa. Increased seeding rates normally are not economically justified when well-prepared firm seedbeds are used. However, higher seeding rates sometimes are used to compensate for poor soil preparation or seeding methods. Increase rates to 15-20 lb/a (17-22 kg/ha) for drilling and 20-25 lb/a (22-28 kg/ha) when broadcasting.
AutotoxicityAttempts to reestablish alfalfa immediately following a previous alfalfa crop or to thicken old alfalfa stands sometimes have resulted in establishment failures. These failures have been related to autotoxicity. Autotoxicity exists when alfalfa has lower germination, poorer establishment, and/or lower production when grown immediately following alfalfa. Autotoxicity effects are attributed to plant exudates and by-products of decomposition. A period of 2 or more weeks between plowing and seeding or 3 or more weeks after herbicide killing of alfalfa and seeding can be used to avoid autotoxicity.
Inoculation and Nitrogen Fixation
The presence of effective nodules (picture link) on the roots of the plants is essential to a vigorous, productive stand. These nodules are formed by bacteria (Rhizobium meliloti) that are able to fix nitrogen from the air for use by the alfalfa plants. These bacteria may be present in fields where alfalfa has been grown recently, but all strains of bacteria are not equally effective. All alfalfa seed should be inoculated with a fresh commercial inoculum> (vendor link) immediately prior to seeding, regardless of cropping history of the land or any previous inoculation of the seed. Inoculated seed should be kept cool and moist until planted.
Fertility and pH Requirements
A productive alfalfa crop is a heavy user of plant nutrients. A complete fertilizer program is essential to a long-lived stand. A soil test (fact sheet link) is the first step in planning a fertility program (section link). Applications of fertilizer and lime should be based on the results of a soil test. Lime applications are required on soils having a pH below 6.2.
Apply lime well in advance of seeding, mixing thoroughly with the surface 6 inches of soil. Fall applications provide time for soil reaction to take place and avoid the spring rush that often will delay planting.
Phosphorus can be applied by banding ½ to 1 inch to the side or below the seed when seeding, but is most often applied by broadcasting, followed by shallow incorporation, just prior to seeding.
Potassium, sulfur, and boron should be worked into the seedbed just prior to the seeding operation. Potassium and boron should not be banded near the seed. Nitrogen fertilizer is not required on legume forages because of the fixation of atmospheric nitrogen by effective nodules. Addition of nitrogen fertilizer will reduce the effectiveness of the natural nitrogen-fixing mechanism. If applied as part of other fertilizers (i.e. single ammonium phosphate), N application should not exceed 40 lb/a (45 kg/ha). Specific fertilizer recommendations based upon soil test data are provided in state Extension Service fertilizer guides (link to fertilizer guides).
Germination and Seedling Development
Alfalfa’s primary root emerges near the hilum (picture link) and penetrates the soil as an unbranched taproot. As the hypocotyedonary area straightens and elongates, the cotyledonary leaves emerge aboveground (picture link). The first foliar leaf is simple (unfoliate), with a slender petiole. Subsequent foliar leaves are compound and usually trifoliolate . Vegetative buds develop in the axils of the cotylendonary leaves and subsequent foliar leaves.
The timing of the removal of top growth of alfalfa by mowing or grazing has a profound influence on the productivity and length of life of an alfalfa stand. The large taproot of the alfalfa plant is a storage organ for food reserves that are needed to renew top growth in the spring and after each cutting. The maintenance of food reserves is necessary to keep the stand vigorous and productive. The amount of food reserves in alfalfa roots increases as the interval between cuttings is increased to 35 days, after which it declines. Cutting more frequently than 28 days or continuous grazing will lower the root reserve and weaken the stand (graph link).
Cutting at the proper stage of growth has a greater influence on hay quality (section link), total production, and life of the stand than any other management decision (table link). The highest quality hay is cut in the early bud stage when the plants have a high proportion of leaves that are rich in protein. As the plants mature, the stems become more coarse and constitute a larger proportion of the total plant, protein percentage decreases, and fiber content increases. However, alfalfa cut at the pre-bud stage produces less forage per acre and continued early cutting seriously weakens the stand.
For first cutting, the bloom is often delayed by cool weather and low light intensity. The appearance of new bud growth at the crown (near the soil surface) (picture link) or the yellowing of lower leaves is usually a better indicator of time to make the first cutting.
(picture links for each)
More than 20 diseases are serious problems for alfalfa in the US. These include fungal and bacterial wilts, leaf spots, crown and root rots, viruses, and nematodes. Important wilts are bacterial wilt [caused by Corynebacterium insidiosum (McCull.) H. L. Jens], fusarium wilt [caused by Fusarium oxysporum Schlecht. f. sp. medicaginis (Weimer) Snyd. & Hans.], and verticillium wilt [caused by Verticillium albo-atrum Reinke & Berth]. The most serious leaf spots are common leaf spot [caused by Pseudopeziza medicaginis (Lib.) Sacc.], lepto leaf spot [caused by Leptosphaerulina briosianna (Pollacci) J. H. Graham & Luttrell], stemphylium leaf spot [caused by Stemphylium botryosum Wallr.], and summer blackstem [caused by Cercospora medicaginis Ellis & Everh].
Important crown and root rots include anthracnose [caused by Colletotrichum trifolii Bain & Essary], Aphanomyces spp. root rot, spring blackstem [caused by Phoma medicaginis Malbr. & Roum. var. Medicaginis], phytophthora root rot [caused by Phytophthora megasperma Drechs.], rhizoctonia diseases [caused by Rhizoctonia solani Kuehn.], and sclerotina crown and stem rot [caused by Sclerotina trifoliorium sensu Kohn]. Alfalfa mosaic (Alfalfa Mosaic Virus complex), is the primary virus disease.
Alfalfa stem nematode [ Ditylenchus dipsaci (Kuhn) Filpjev], root-knot nematodes (Meloidogyne spp.), and root-lesion nematodes (Pratylenchus spp.) are the most prevalent nematode species on alfalfa.
Resistant cultivars are available for most of the diseases and nematodes listed. (CASC list link)
(picture links for each)
There are a number of insects pests on alfalfa in the US. The insect pests that interfere with forage production include the potato leafhopper, Empoasca fabae (Harris); the alfalfa weevil, Hypera postica (Gyll.); the spotted alfalfa aphid; the pea aphid, A. kondoi Shinji; the alfalfa plant bug, Adelphocoris lineolatus (Goeze); and the meadow spittlebug, Philaenus spumarius (L.). The potato leafhopper is the most problematic pest and causes damage throughout most alfalfa-producing areas in the eastern and central US. It causes yellowing of the foliage and stunting of stems. The damage results in significant losses in yield and forage quality, especially loss in carotene.
Information from: forages.css.orst.edu/Topics/Species/Legumes/Alfalfa/International_Fact_Sheet.html