Alfalfa
Alfalfa, lucerne, Medicago sativa is a perennial flowering plant in the legume family Fabaceae. It is cultivated as an important forage crop in many countries around the world and is used for grazing, hay, and silage, as well as a green manure and cover crop. It has also been cultivated as livestock fodder since at least the era of the ancient Greeks and Romans. Alfalfa has clusters of small purple flowers followed by fruits spiraled in two to three turns containing 10–20 seeds. It is native to warmer temperate climates.
Description
Alfalfa has an autotetraploid genome with tetrasomic inheritance. It is a perennial forage legume which normally lives four to eight years but can live more than 20 years, depending on variety and climate. The plant grows to a height of up to. Its root system typically grows to a depth of depending on subsoil constraints but sometimes grows to a depth of more than to reach groundwater.Alfalfa is a small-seeded crop and has a slowly growing seedling, but after several months of establishment, it forms a tough "crown" at the top of the root system. This crown contains shoot buds that enable alfalfa to regrow many times after being grazed or harvested.
Etymology
According to Merriam-Webster, English use of alfalfa dates to 1791 and derives from the identical cognate in Spanish, whose origin is "", of an Arabic dialect, otherwise presented as الفصفصة. Harper at Etymology Online suggests "alfalfa" derives from the same Spanish cognate but dates to 1845, believing the Spanish predecessor of the cognate to be "alfalfez". Harper also ascribes its origin to Arabic, citing "Iberian sources", and offers the definition of the Arabic as "fresh fodder". This suggests that the Arabic word might derive from "an Old Iranian compound" meaning "horse food".Lucerne, or lucern, as a synonym for alfalfa was borrowed from French, first appearing in written English in 1652. The French word was itself a borrowing from the Occitan luzerno, meaning "glowworm", likely a reference to the bright yellow seeds of some strains of alfalfa.
History
Alfalfa is believed to have originated in south-central Asia and was first cultivated in Central Asia. According to Pliny, it was introduced to Greece in about 490 BC when the Persians invaded Greek territory. Alfalfa cultivation is discussed in the fourth-century AD book Opus Agriculturae by Palladius, stating: "One sow-down lasts ten years. The crop may be cut four or six times a year... A jugerum of it is abundantly sufficient for three horses all the year... It may be given to cattle, but new provender is at first to be administered very sparingly, because it bloats up the cattle."The medieval Arabic agricultural writer Ibn al-'Awwam, who lived in Spain in the later 12th century, discussed how to cultivate alfalfa, which he called الفصفصة. A 13th-century general-purpose Arabic dictionary, Lisān al-'Arab, says that alfalfa is cultivated as an animal feed and consumed in both fresh and dried forms.
In the 16th century, Spanish colonists introduced alfalfa to the Americas as fodder for their horses.
In the North American colonies of the eastern US in the 18th century, it was called "alfalfa", and many trials at growing it were made, but generally without sufficiently successful results. Relatively little is grown in the southeastern US today. Alfalfa seeds were imported to California from Chile in the 1850s. That was the beginning of a rapid and extensive introduction of the crop over the western US and introduced the word "alfalfa" to the English language. Since North and South America now produce a large part of the world's output, the word "alfalfa" has been slowly entering other languages.
Ecology
Alfalfa is considered an insectary plant and may help other crops such as cotton because it harbours predatory and parasitic insects that would protect the other crop if the two were interplanted. Harvesting the alfalfa by mowing the entire crop area destroys the insect population; this can be avoided by mowing in strips so that part of the growth remains.Alfalfa develops extensive taproots that can extend around 6 feet per year in loose soil. This allows the plant to access soil moisture that is not accessible to plants with shallow root systems, making it more resistant to droughts and soil erosion. This depth of root system, and perenniality of crowns that store carbohydrates as an energy reserve, makes it very resilient.
Alfalfa exhibits autotoxicity, which means it is difficult for alfalfa seed to grow in existing stands of alfalfa. Therefore, alfalfa fields are recommended to be rotated with other species before reseeding. The exact mechanism of autotoxicity is unclear, with medicarpins and phenols both seeming to play a role. The level of autotoxicity in soil depends on soil type, cultivar and age of the previous crop. A soil assay can be used to measure autotoxicity. Resistance to autotoxicity also varies by cultivar, a tolerant one being 'WL 656HQ'.
Pests and diseases
Like most plants, alfalfa can be attacked by various pests and pathogens. Diseases often have subtle symptoms which are easily misdiagnosed and can affect the leaves, roots, stems, and blossoms.Some pests, such as the alfalfa weevil, aphids, and potato leafhopper, can reduce alfalfa yields dramatically, particularly with the second cutting when weather is warmest. Spotted alfalfa aphid, broadly spread in Australia, sucks sap and injects salivary toxins into the leaves. Registered insecticides or chemical controls are sometimes used to prevent this, and labels will specify the withholding period before the forage crop can be grazed or cut for hay or silage. Alfalfa is susceptible to root rots, including Phytophthora, Rhizoctonia, and Texas root rot. Alfalfa is also susceptible to downy mildew caused by the oomycete species Peronospora aestivalis.
Cultivation
Alfalfa is widely grown throughout the world as forage for cattle. It is most often harvested as hay but can also be made into silage, grazed, or fed as greenchop. Alfalfa usually has the highest feeding value of all common hay crops. It is used less frequently as pasture. When grown on soils where it is well-adapted, alfalfa is often the highest-yielding forage plant, but its primary benefit is the combination of high yield per hectare and high nutritional quality.Its primary use is as feed for high-producing dairy cows because of its high protein content and highly digestible fiber, and secondarily for beef cattle, horses, sheep, and goats. Alfalfa hay is a widely used protein and fiber source for meat rabbits. In poultry diets, dehydrated alfalfa and alfalfa leaf concentrates are used for pigmenting eggs and meat because of their high content in carotenoids, which are efficient for colouring egg yolk and body lipids. Humans also eat alfalfa sprouts in salads and sandwiches. Dehydrated alfalfa leaf is commercially available as a dietary supplement in several forms, such as tablets, powders and tea. Fresh alfalfa can cause bloating in livestock, so care must be taken with livestock grazing on alfalfa.
Alfalfa engages in symbiotic nitrogen fixation with nitrogen-fixing bacteria called rhizobia, including Sinorhizobium meliloti. This symbiosis results in the formation of indeterminate nodules which grow on the root on the root hairs. S. meliloti, once inside the nodule, will terminally differentiate into bacteroids in which they lose the ability to return to free-living growth in soil. The bacteroids fix atmospheric nitrogen into bioavailable forms such as ammonia. Bacteroids are provided with carbohydrates for growth and return usable nitrogen to the plant. This mutualistic interaction improves soil nitrogen fertility as plant matter is accumulated in the surrounding soil.
Symbiosis allows Alfalfa to produce a nutritious feed regardless of available nitrogen in the soil. Its nitrogen-fixing ability and its use as an animal feed greatly improve agricultural efficiency.
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 sustained levels of potassium and phosphorus to grow well. It is moderately sensitive to salt levels in both the soil and irrigation water, although it continues to be grown in the arid southwestern United States, where salinity is an emerging issue. 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 is recommended, with differences based upon region, soil type, and seeding method. A nurse crop is sometimes used, particularly for spring plantings, to reduce weed problems and soil erosion, but can lead to competition for light, water, and nutrients.
In most climates, alfalfa is cut three to four times a year, but it can be harvested up to 12 times per year in Arizona and southern California. Total yields are typically around in temperate environments, but yields have been recorded up to. Yields vary with region, weather, and the crop's stage of maturity when cut. Later cuttings improve yield, but with reduced nutritional content.
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 easier for use in transportation, storage, and feed. Ideally, the first cutting should be taken at the bud stage, and the subsequent cuttings just as the field is beginning to flower, or one-tenth bloom because carbohydrates are at their highest. When using farm equipment rather than hand-harvesting, a swather cuts the alfalfa and arranges it in windrows. In areas where the alfalfa does not immediately dry out on its own, a machine known as a mower-conditioner is used to cut the hay. The mower-conditioner has a set of rollers or flails that crimp and break the stems as they pass through the mower, making the alfalfa dry faster. After the alfalfa has dried, a tractor pulling a baler collects the hay into bales.Several types of bales are commonly used for alfalfa. For small animals and individual horses, the alfalfa is baled into small, two-string bales, commonly named by the strands of string used to wrap it. Other bale sizes are three-string, and so on up to half-ton "square" bales – actually rectangular, and typically about. Small square bales weigh from depending on moisture, and can be easily hand separated into "flakes". Cattle ranches use large round bales, typically in diameter and weighing from. These bales can be placed in stable stacks or in large feeders for herds of horses or 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 they can be handled with a grapple on the tractor's front-end loader.
When used as feed for dairy cattle, alfalfa is often made into haylage by a process known as ensiling. Rather than being dried to make dry hay, the alfalfa is chopped finely and fermented in silos, trenches, or bags, where the oxygen supply can be limited to promote fermentation. The anaerobic fermentation of alfalfa allows it to retain high nutrient levels similar to those of fresh forage and is more palatable to dairy cattle than dry hay. In many cases, alfalfa silage is inoculated with different strains of microorganisms to improve the fermentation quality and aerobic stability of the silage.