Alfalfa
From Wikipedia, the free encyclopedia
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 Medicago sativa
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| Medicago sativa L. |
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M. sativa subsp. ambigua |
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- For the Our Gang (Little Rascals) character, see Carl Switzer. For the place, see Alfalfa, Oklahoma.
Alfalfa (Medicago sativa), also known as Lucerne, Purple Medick and Trefoil, is a perennial flowering plant cultivated as an important forage crop.
Alfalfa lives from five to twelve years, depending on variety and climate. It is a cool season perennial legume, growing to a height of 1 meter. It resembles clover with clusters of small purple flowers. It also has a deep root system sometimes stretching to 4.5 metres. This makes it very resilient, especially to droughts. It has a tetraploid genome.
Alfalfa is native to Iran, where it was probably domesticated during the Bronze Age to feed horses being brought from Central Asia. It came to Greece around 490 B.C. being used as a horse feed for Persian army. It was introduced from Chile to the United States around 1860. It is widely grown throughout the world as forage for cattle, and is most often harvested as hay. Alfalfa has the highest feeding value of all common hay crops, being used less frequently as pasture. Like other legumes, its root nodules contain bacteria, like Rhizobium, with the ability to fix nitrogen, producing a high-protein feed regardless of available nitrogen in the soil.
Its wide cultivation beginning in the seventeenth century was an important advance in European agriculture. Its symbiotic relationship with nitrogen-fixing bacteria and use as animal feed greatly improved agricultural efficiency. When grown on soils where it is well-adapted, alfalfa is the highest yielding forage plant.
Alfalfa is one of the few plants that exhibit autotoxicity. Alfalfa seed will not grow in existing stands of alfalfa because of this. Therefore, alfalfa fields must be cleared or rotated before reseeding.
Alfalfa sprouts are used as a salad ingredient in the United States and Australia. Tender shoots are eaten in some places as a leaf vegetable. Human consumption of older plant parts is limited primarily by very high fiber content. Dehydrated alfalfa leaf is commercially available as a dietary supplement in several forms, such as tablets, powders and tea. Alfalfa is believed to be a galactagogue.
In the United States, the leading Alfalfa growing states are Wisconsin and California, with most of the latter state's production occurring in the Mojave Desert by means of irrigation provided by the California Aqueduct.
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[edit] Culture
Alfalfa can be sown in spring or fall, and does best on well-drained soils with a neutral pH of 6.8–7.5. Alfalfa requires a great deal of potash. Soils low in fertility should be fertilized with manure or a chemical fertilizer. Usually a seeding rate of 13–17 kg/hectare (12–15 lb/acre) in climatic acceptable regions and a rate of 22 kg/hectare (20 lb/acre) in southern regions is used. A nurse crop is often used, particularly for spring plantings, to reduce weed problems. Herbicides are sometimes used instead. A genetically modified variety which is tolerant to the herbicide Roundup has been developed and will be sold in the United States pending deregulation.
In most climates, alfalfa is cut three or four times a year. Total yields are typically around 8 tonne/hectare (4 ton/acre) but vary regionally and with weather, and with stage of maturity when cut. Later cuttings improve yield but reduce nutritional content.
The potato leafhopper can reduce alfalfa yields dramatically, particularly with the second cutting when weather is warmest. Chemical controls are sometimes used to prevent this. Alfalfa is also susceptible to Texas Root Rot.
Alfalfa seed production requires cultured pollinators to be provided for the fields when in bloom. Alfalfa pollination is somewhat problematic because the keel of the flower trips to help pollen transfer to the foraging bee, striking them in the head. Honeybees apparently do not like being struck, and often learn to defeat this action by drawing nectar from the side of the flower, thus pollination is not accomplished. The majority of the pollination is accomplished by young bees that have not yet learned the trick of robbing the flower without tripping it. When honeybees are used for pollination, the beehives are stocked at a very high rate to maximize the number of young bees.
Today the alfalfa leafcutter bee is increasingly used to circumvent this problem. As a solitary but gregarious bee species, it does not build colonies or store honey, but is a very efficient pollinator of alfalfa seed. Nesting is in individual tunnels in wooden or plastic material, supplied by the alfalfa seed growers.
A smaller amount of alfalfa seed is pollinated by the alkali bee, mostly in the northwestern USA. It is cultured in special beds near the seed fields. These bees also have their own problems. They are not portable like honeybees; they take several seasons to build up, when fields are planted in new areas. Honeybees are still trucked to many of the fields at bloom time.
[edit] Harvesting
When alfalfa is to be used as hay, it is usually cut and baled. Loose haystacks are still used in some areas, but bales are much easier to transport. Ideally, the hay is cut just as the field is beginning to flower. When using farm equipment rather than hand-harvesting, the process begins with a swather, which cuts the alfalfa and arranges it in windrows. In areas where drying down of the alfalfa is problematic and slow, a machine know as mower-conditioner is used to cut the hay. The mower-conditioner has either a set of rollers or flails through which the hay passes after being cut which crimps or breaks the stems in order to facilitate faster dry down of the hay. After it has dried, a tractor pulling a baler collects the hay into bales. There are three types of bales commonly used for alfalfa. Small "square" bales—actually rectangular, and typically about 40 x 45 x 100 cm (14 in x 18 in x 38 in)—are used for small animals and individual horses. The small square bales weigh between 25–30 kg (50–70 pounds) depending on moisture, and can easily be hand separated into "flakes".
Cattle ranches use large round bales, typically 1.4 to 1.8 m (4 to 6 feet) in diameter and weighing up to 500–1,000 kg. These bales can be placed in stable stacks, placed in large feeders for herds of horses, and unrolled on the ground for large herds of cattle. The bales can be loaded and stacked with a tractor using a spike, known as a bale spear, that pierces the center of the bale, or with a grapple (claw) on the tractor's front-end loader.
A more recent innovation is large "square" bales, roughly the same proportions as the small squares, but much larger. The bale size was set so that stacks would fit perfectly on a large flatbed truck.
When used as feed for dairy cattle it is often made into haylage by a process known as ensiling. Rather than drying it down to the level of dry hay it is chopped finely and put into silos, trenches, or bags, where the oxygen supply can be limited allowing it to ferment. This allows it to remain in a state in which the nutrient levels are closer to that of fresh forage, and is more palatable in the high performance diet of dairy cattle.
[edit] Varieties
Considerable research and development has been done with this important plant. The cultivar 'Vernal' was introduced around 1953 and was the standard for years. Many better public and private varieties are available now, and are adapted to the needs of particular climates. Most alfalfa cultivars contain genetic material from Sickle Medick (M. falcata), a wild variety of alfalfa which naturally hybridizes with M. sativa to produce Sand Lucerne (M. sativa ssp. varia). This species may bear either the purple flowers of alfalfa or the yellow of sickle medick, and is so called for its ready growth in sandy soil.
Most of the improvements in alfalfa over the last decades have been in disease resistance, improved ability to overwinter in cold climates, and multileaf traits. Disease resistance is important because it improves the usefulness of alfalfa on poorly drained soils, and during wet years.
Multileaf alfalfa has more than three leaflets per leaf. It has a higher nutitional content by weight because there is relatively more leafy matter for the same amount of stem.
[edit] External links
- Photos of moving honeybees to alfalfa
- Use of the Alfalfa Leafcutter Bee Growing in California
- Roundup Ready™ Alfalfa
- Problems with genetically modified Alfalfa
- University of Wisconsin Forage Research and Extension
- University of California Alfalfa Workgroup
