Difference between revisions of "Alfalfa"
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 Medicago sativa | ||||||||||||||||||
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| Medicago sativa L. | ||||||||||||||||||
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| M. sativa subsp. ambigua M. sativa subsp. microcarpa |
Alfalfa (Medicago sativa), also known as Lucerne, Purple Medic and Trefoil (Arabic: البرسيم الحجازي), is a perennial flowering plant cultivated as an important forage crop.
Alfalfa is one of the most important legumes used in agriculture. The US is the largest alfalfa producer in the world. The leading alfalfa growing states (within the U.S.A.) are California, South Dakota, and Wisconsin. The upper Midwestern states account for about 50% of US production, the North eastern states 10%, and western states 40% of US production, the latter mostly under irrigation. Alfalfa is not very important in the Southeastern states. However, alfalfa has a wide range of adaptation and can be grown from very cold northern plains to high mountain valleys, from rich temperate agricultural regions to Mediterranean climates and searing hot deserts.
Alfalfa lives from three 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 a plant that exhibits autotoxicity, which means that it is difficult for alfalfa seed to grow in existing stands of alfalfa. Therefore, it is recommended that alfalfa fields be cleared or rotated before reseeding.
Its primary use is for dairy production, followed by beef, sheep, horses and goats, but it is sometimes used for human consumption. Alfalfa sprouts are used as a salad ingredient in the United States, Australia and New Zealand. 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.
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, but correction of pH is particularly important. Usually a seeding rate of 13 – 20 kg/hectare (12 – 25 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 is currently sold in the United States pending deregulation.
In most climates, alfalfa is cut three to four times a year but is harvested up to 12 times per year in Arizona and Southern California. Total yields are typically around 8 tonne/hectare (4 ton/acre) but yields have been recorded up to 20 tonnes/ha (16 ton/acre). Yields vary due to region and with weather, and with stage of maturity when cut. Later cuttings improve yield but reduce nutritional content.
Alfalfa is considered an 'insectary' due to the large number of insects which are found there. Some pests such as Alfalfa weevil, aphids, and 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 root rots including phytophora, rhizoctonia, and Texas Root Rot.
Alfalfa seed production requires pollinators to be present in 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. Western honey bees do not like being struck in the head repeatedly, and often learn to defeat this action by drawing nectar from the side of the flower, thus pollination is not accomplished.[1] 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 honey bees 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.[1]
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 honey bees; they take several seasons to build up, when fields are planted in new areas.[1] Honey bees are still trucked to many of the fields at bloom time.
- Main article: List of alfalfa diseases
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 and are easier to keep hold of when being stored. 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.
Varieties
Considerable research and development has been done with this important plant. Older cultivars such as 'Vernal' have been the standard for years, but many better public and private varieties are available now, and are adapted to the needs of particular climates. Private companies release many new varieties each year in the US.
Fall Dormancy is a major characteristic of alfalfa varieties. More 'dormant' varieties have reduced growth in the fall, a response due to low temperatures and reduced day lengths. 'Non-dormant' varieties exhibit winter growth activity, and therefore are grown in long-seasoned environments such as Mexico, Arizona, and Southern California, whereas 'dormant' lines are grown in the Upper Midwest, Canada, and the Northeast. 'Non-dormant' lines are susceptible to winter-kill in cold climates, and have poorer persistence, but can be higher yielding.
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. These lines may have a higher nutritional content by weight because there is relatively more leafy matter for the same amount of stem.
Modern alfalfa varieties have probably a wider range of insect, disease, and nematode resistance than many other agricultural species. The North American Alfalfa Improvement Conference records new varieties and encourages communication between breeders.
References
- In Of Mice and Men, the popular novella authored by John Steinbeck, Lenny becomes increasingly obsessed with growing Alfalfa for his rabbits for if he ever gets a farm with George.
