Alfalfa

A perennial legume, alfalfa (Medicago sativa) is a member of the Fabaceae or Leguminosae family and is related to clover, pea, bean, soybean, lentil, chickpea, lupin, peanut, vetch, and cowpea. Known as the Queen of Forages because it fixes nitrogen in the soil and feeds livestock, alfalfa is the world’s most widely grown legume. In 1753, Swedish naturalist Carl Linnaeus named alfalfa, the genus Med- icago deriving from the Latin medica, denoting the belief that the plant had originated in Mesopotamia (now Iraq). Italians knew alfalfa as erbo medica, meaning the “median herb.” In Spanish, alfalfa is mielgo and in Turkish kayseri trefoil. Indians refer to alfalfa as Ashue-Bal, meaning “strength to horses,” surely a reference to the practice of feeding the legume to equines. The Chinese knew alfalfa as mu-su. The Arabic word ratba means “green alfalfa,” and quatt means “alfalfa hay.” The Persian word aspo-asti for alfalfa means “horse fodder,” suggesting the same use as in India. From the Persian, the Babylonians derived aspasti for alfalfa. In turn, the Arabs derived the term “alfalfa” from aspasti. The Syrians used a similar word, aspasta, to refer to alfalfa. The Swiss and people in other parts of Europe, South Africa, New Zealand, and Australia knew alfalfa as lucerne, perhaps because the Swiss grew alfalfa in the region of Lake Lucerne. Another

Alfalfa (iStockPhoto)

possibility is that the term derived from the Lucerne River in Italy. Alphonse de Candolle, the 19th-century French botanist, rejected both possibilities, instead asserting that lucerne derived from the French laouzerde.

Origin and Diffusion

Several scholars believe that alfalfa was the only forage grown in prehistory even though written records of alfalfa, when they appeared, do not date from the beginning of the historical period. By one account we have seen, alfalfa originated in Mesopotamia. By another, Iran was the homeland of the legume. Yet another broadens the geography, maintaining that alfalfa originated in western Asia, Iran, Transcaucasia, and Turkmenistan. The legume grows wild from China to Spain and from Sweden to North Africa, though humans may have assisted it in diffusing so widely. If this is correct, the wild plants may have escaped from cultivation. Having evolved in a region of cold winters and hot, dry, short summers, alfalfa tolerates cold weather, though curiously it does not yield well in hot weather, instead becoming dormant. One scientist pinpoints two regions of origin. The first, Transcaucasia, gave rise to the varieties of alfalfa grown in Europe. Having evolved in a region of frigid winters, these varieties are hardy. The second region, Central Asia, had a dry climate. The varieties that evolved there did not acquire resistance to the fungal diseases that accompanied humidity. Another school of thought traces the lineage of alfalfa to Medicago falcate. The varieties that descended from this proto-alfalfa were hardy, drought tolerant, and resistant to diseases. Alfalfa is drought tolerant because the taproot, penetrating 20 feet into the soil, absorbs underground water when the topsoil is dry. The plant tolerates drought and cold, moreover, because it becomes dormant during adverse conditions.

The earliest written reference to alfalfa dates to 1300 BCE in Turkey. Given that the cultivation of alfalfa might have begun in prehistory, it seems surprising that there are no earlier records of it. About this time, the Hittites fed the legume to livestock during winter, regarding it as nutritious. By the first millennium BCE, the people of northwestern Iran widely cultivated alfalfa. It was the fodder of cavalry and chariot horses in Iran, Greece, and Rome. Greek dramatist Aristophanes (440380 BCE) and fourth-century Greek philosopher Aristotle mentioned alfalfa, implying that it was cultivated in Greece. In the fourth century BCE, Aristotle’s pupil Greek botanist Theophrastus related the story of alfalfa’s introduction to Greece. According to him, the Persians, invading Greece in the fifth century, planted alfalfa to feed their warhorses and cattle. Although the Greeks ejected the Persians, they adopted the practice of cultivating alfalfa for forage. In turn the Romans, in the second century BCE, adopted alfalfa from the Greeks. In the first century BCE, Roman agricultural writer Varro and Roman poet Virgil mentioned alfalfa. Varro recommended that stockmen seed it at a rate of 34 pounds per acre. He observed that alfalfa attracted bees. In the first century CE, Roman encyclopedist Pliny the Elder repeated Theophrastus’s account that the Persian army brought alfalfa to Greece. He recommended that farmers plant alfalfa in well-drained soil, add lime to the soil, and cut alfalfa upon flowering. Pliny’s contemporary, Roman agricultural writer Columella, cautioned against overfeeding alfalfa to livestock for fear of bloating. He understood that alfalfa improved the soil, though the Romans had no knowledge of nitrogen fixation. Columella believed that alfalfa could cure livestock of various ailments. One authority estimates the yield of alfalfa at 12 tons per acre in Rome. By one account, Columella planted alfalfa in southern Spain. By another, the Romans introduced alfalfa to Gaul (now France), Germany, and Switzerland in addition to Spain. The fall of Rome marked a decline in alfalfa culture in parts of Europe, though Arabs grew it in Spain in addition to North Africa. If Columella planted alfalfa in Spain in the first century, the Arab introduction in the eighth century must have marked a reintroduction of the crop. Medieval records contain few references to alfalfa, suggesting that it was not widely grown during the Middle Ages. Renaissance stockmen showed a renewed interest in the legume. In the 16th century, the Spanish reintroduced alfalfa to Italy and in about 1550 to France. In 1565, farmers spread alfalfa to Belgium and the Netherlands, in 1650 to England, in 1750 to Germany and Austria, in 1770 to Sweden, and in the 18th century to Russia.

Outside Europe, the Chinese adopted alfalfa from Turkestan in 126 BCE. In the 16th century, the Spanish introduced alfalfa to Mexico and Peru. By 1775, stockmen grew alfalfa in Chile, Argentina, and Uruguay. From Mexico, missionaries brought the legume to Texas, Arizona, New Mexico, and California. Another account holds that Chile was the source of the Californian introduction in the 19th century. In 1851, farmer W. E. Cameron planted alfalfa in the Sacramento River Valley in California, though its introduction to the state may have occurred earlier. By 1858, Cameron had 270 acres of alfalfa. Alfalfa thrived in the dry climate of the American Southwest. In 1836, Major Jacob Downing planted alfalfa in Colorado. By 1894, stockmen widely planted alfalfa in Kansas. Farmers began growing alfalfa in Ohio in 1886, in Montana by 1890, and in Iowa and Missouri by 1900. In the eastern United States, immigrants made separate introductions of the forage to Georgia in 1736, North Carolina in 1739, and New York in 1791. In Virginia, accomplished gardener Thomas Jefferson in 1793 and George Washington in 1798 planted alfalfa. Yet the acidic soil and humidity of the eastern United States were not ideal for alfalfa, and by 1899 farmers grew only a small portion of alfalfa east of the Mississippi River. By contrast, the land west of the Mississippi River totaled the majority of alfalfa acreage in 1949.

Attributes and Nutrients

Adapted to temperate regions, alfalfa does not tolerate temperatures above 95°F. Better adapted to cold weather, alfalfa withstands temperatures as low as 23°F when it is not hardened and as low as -4°F when it has undergone hardening in autumn. The short days of autumn spur the plant to harden. Alfalfa initiates hardening when temperatures dip below 50°F. A hydrated alfalfa plant cannot endure temperatures below 28°F without water freezing in its cells. In response to cold weather, alfalfa reduces the amount of water in its cells and so can withstand colder temperatures. For this reason, drought aids alfalfa in hardening. Soil moisture no greater than 50 percent of saturation helps alfalfa harden. Because saturated soil reduces hardiness, farmers should not irrigate alfalfa in autumn. Where snow insulates the land, alfalfa does not develop maximum hardiness. Excessive nitrogen and a dearth of other nutrients in the soil impair hardiness. The application of potassium and phosphorus to the soil increases hardiness. Plants with a store of carbohydrates and amino acids for the lean months of winter are hardy.

Removing more nutrients from the soil than grains, alfalfa is a heavy feeder. In 1988, one scientist estimated that the U.S. alfalfa crop removed 1.7 million tons of potassium from the soil. This amount totaled 40 percent of the potassium applied to all crops in the United States and more than twice the amount applied to corn. Alfalfa removes 10 times more potassium from the soil than an equivalent amount of corn. Cool temperatures slow the uptake of nitrogen, phosphorus, and sulfur. Alfalfa leaves contain less phosphorus, potassium, iron, boron, copper, zinc, and manganese and more calcium and magnesium in cool rather than warm weather.

Alfalfa favors a soil pH between 6.6 and 7.5, though the pH may be as low as 4 if the soil has enough calcium. As a rule, however, the yield decreased when the pH falls below 5.2 because aluminum, iron, and manganese may reach toxic levels in acidic soil. A neutral pH reduces the solubility and uptake of these elements. The addition of lime to acidic soil increases the availability of calcium, magnesium, phosphorus, and molybdenum. One recommendation holds that the farmer should add lime to the soil at least 26 weeks before planting or immediately after planting.

In addition to potassium, alfalfa is a heavy feeder of nitrogen. The legume removes more nitrogen from the soil than any other nutrient, yet the bacteria that inhabit the nodules of the roots make good much of this loss by fixing nitrogen in the soil. By one estimate, alfalfa removes 980 pounds of nitrogen per acre. One study found that alfalfa obtains 43-64 percent of its nitrogen from the bacteria in its nodules. Because of nitrogen fixation, the crops that follow alfalfa in rotation yield well. Corn in rotation with alfalfa needs 70 percent less nitrogen applied as fertilizer than corn grown in monoculture.

Alfalfa needs less phosphorus than nitrogen and absorbs it in the form of orthophosphate. The farmer should apply phosphorus at the time of planting. One scientist recommends the application of manure to the soil as a source of phosphorus. Farmers in the Pennsylvania Alfalfa Growers Program applied manure from dairy cows to the soil. The reader may remember that alfalfa is a heavy feeder of potassium. Young plants are ravenous in their appetite for the element. Some farmers applied potassium twice per year—once in spring and again in autumn—though one scientist believes that the number of applications does not affect yield. Alfalfa absorbs potassium in the topsoil more efficiently than at depth. Potassium chloride is the most common source of potassium, though one scientist favors potassium sulfate because it does not add chlorine, which can be toxic to alfalfa, to the soil.

Alfalfa absorbs more calcium and magnesium than do grains. Being rich in these nutrients, alfalfa entices some stockmen to feed it rather than grain to their animals. Limestone and dolomite are the chief sources of calcium and magnesium. Soils with too little organic matter may lack sulfur. Cool weather, acidic soil, or drought may limit the availability of sulfur, though it is abundant enough in most soils so that the farmer need apply it only every third year.

Breeding and Cultivars

The discovery of new varieties aided alfalfa in its spread throughout the United States and Canada. In 1857, German immigrant Wendelin Grimm brought a new cultivar, named Grimm in his honor, to Minnesota. A hardy variety, Grimm was ideal for the northern United States and Canada. The Minnesota Agricultural Experiment Station sent Grimm to other states, promoting its cultivation.

In 1908, Canadians began cultivating Grimm. Despite its hardiness, Grimm was susceptible to bacterial wilt. Farmers grew Baltic, a hardy variety named for Baltic, South Dakota, in the northern United States. Baltic, like Grimm, was susceptible to bacterial wilt. From Baltic, the Michigan Agricultural Experiment Station selected Hardigan, a variety prized for its hay. Like Baltic and Grimm, Hardigan was vulnerable to bacterial wilt. A third hardy variety was Cossack, which the U.S. Department of Agriculture imported from Russia in 1907. Although not resistant to bacterial wilt, Cossack was less susceptible than Grimm. Even hardier than Grimm was Ladak, which the U.S. Department of Agriculture imported from India in 1910 and which farmers cultivated in Ontario, Canada. Somewhat resistant to bacterial wilt, Ladak yielded well on the Great Plains. In 1927, the Arnold brothers of Nebraska planted Hardistan, a hardy variety that was soon grown in Canada. Peruvian alfalfa, unable to tolerate temperatures below 10°F, was confined to the American South and Southwest.

In the mid-19th century, the French introduced alfalfa to South Africa, where it was first used to feed ostriches. South African farmers grew the Provence variety, the name suggesting French origin. They also grew Chinese, a variety from Tibet. Around 1800, alfalfa from Europe or Argentina was introduced to New Zealand, where Marlborough was the chief cultivar. In the 18th century, farmers cultivated alfalfa in the Hunter and Peel river valleys in Australia. By 1833, farmers in New South Wales boasted 2,000 acres and by 1920 100,000 acres. Australians grew primarily the variety Hunter, a derivative of Provence, Smooth Peruvian, Arabian, or American Common.

Since 1956, the genetic improvement of alfalfa through breeding has contributed only 3 percent to the increase in yield. The gain in yield has been smaller for alfalfa than for grains. This state of affairs may have resulted from the emphasis on breeding alfalfa resistant to diseases and pests rather than for yield and from the fact that scientist know less about the genetics of alfalfa than of corn. As with corn, hybrid crosses of alfalfa varieties display heterosis.

The efforts to breed disease-resistant cultivars began in the 1930s when scientists identified Ladak and the Turkestan varieties as sources of resistance to bacterial wilt. From them the Nebraska Agricultural Experiment Station and the U.S. Department of Agriculture derived Ranger, and the Kansas Agricultural Experiment Station and the U.S. Department of Agriculture bred Buffalo. Since 1965, virtually all new cultivars have been resistant to bacterial wilt. The variety Vernal is among the most resistant. In 1968, scientists began to breed varieties resistant to anthracnose fungi. In 1974, they released Arc, the first anthracnose-resistant cultivar. Resistant varieties yielded 10 percent more alfalfa than susceptible cultivars where anthracnose is present. In 1977, the discovery of a new race of anthracnose in North Carolina, Maryland, and Virginia spurred scientists to intensify their efforts. Whereas Arc was resistant to only one race, the new Saranac AR was resistant to both.

In 1934, the first variety resistant to the pea aphid was discovered, though a breeding program followed only later. In 1966, scientists released resistant Washore and Apex, in 1967 Dawson and MesiHa, and in 1969 Kanza. Between 1967 and 1983, scientists released more than 75 varieties resistant to the pea aphid. Resistant cultivars yielded two to three times more alfalfa than susceptible varieties under infestation. Kanza, for example, yielded as much as three times more alfalfa than susceptible Buffalo, Ranger, and Vernal. In 1957, scientists released Moaspa and Zia, cultivars resistant to the spotted alfalfa aphid. Farmers grew Zia in New Mexico. Cody, another resistant cultivar, is a derivative of Chilean varieties. Between 1957 and 1983, scientists bred more than 100 resistant varieties. These cultivars have saved growers $35 million per year according to one estimate.

Christopher Cumo

Further Reading

Bolton, J. L. Alfalfa: Botany, Cultivation, and Utilization. New York: Interscience, 1962.

Graumann, H. O., and C. H. Hanson. Growing Alfalfa. Washington, D.C.: U.S. Department of Agriculture, 1954.

Hanson, A. A., D. K. Barnes, and R. R. Hill Jr., eds. Alfalfa and Alfalfa Improvement. Madison, WI: American Society of Agronomy, 1988.

Hanson, C. H., ed. Alfalfa Science and Technology. Madison, WI: American Society of Agronomy, 1972.

 
Source
< Prev   CONTENTS   Source   Next >