Medicago sativa (PROSEA)
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Introduction |
- Protologue: Sp. Pl.: 778 (1753).
- Family: Leguminosae
- Chromosome number: 2n= 32 (tetraploid in cultivated forms), 2n= 16 (diploid in wild forms).
Vernacular names
- Lucerne (En), alfalfa (Am). Luzerne (Fr)
- Philippines: galeria (Visaya)
- Thailand: thua-anfanfa.
Origin and geographic distribution
Lucerne is believed to have originated in the highlands of Transcaucasia, Asia Minor and north-western Iran, and/or Central Asia. It has been cultivated for thousands of years and introduced to most countries of the world. It is only a minor species in South-East Asia.
Uses
Lucerne is the world's most important forage crop and is cultivated mainly to provide feed for ruminants, but is also used as an ingredient of rations for poultry and pigs. Protein is extracted from the forage for consumption by humans and a wide range of animals. Seeds are sprouted for human consumption.
Properties
Lucerne provides highly palatable, highly nutritious forage, hay, silage and pellets. At the early flowering stage, when it is commonly harvested, the dried forage contains 2.5-4.0% N and is 60-70% digestible. There are 400-1000 seeds/g.
Botany
A herbaceous perennial with deeply penetrating taproot. Stems procumbent, ascending to erect, arising from woody base, branching at base and rising to 30-80(-120) cm. Leaf trifoliolate; stipules triangular, 5-15 mm long, pubescent on lower surface, glabrous on upper surface, joined at base, coarsely-toothed; petiole pubescent, 5-30 mm long; leaflets narrow, oblong to ovate or obovate, 8-28 mm × 3-15 mm, dentate near apex, glabrous on upper surface, slightly pubescent on lower surface. Inflorescences in dense racemes containing 10-35 flowers, on peduncles 1-5 cm long; pedicel 1.5-2 mm long; calyx 5-lobed, 3-6 mm long, tube and pointed teeth about equal in length; corolla purple or blue, rarely white, with some yellow-flowered plants in cultivars containing M. falcata genes. Pod curled through 2-5 coils of 3-10 mm in diameter, indehiscent, not spined, containing 2-6 seeds. Seed yellow to brown, kidney-shaped to ovoid, 1-2.5 mm × 1-1.5 mm.
The taxonomy of M. sativa is confused and the cultivated forms may well be a tetraploid of hybrid origin. Because M. sativa is part of a species complex including M. falcata L., M. glutinosa M. v. Bieb. and M. glomerata Balbis, many hybrid forms have erroneously been given specific names.
Most cultivars flower in long days (> 10-12 hours) but vary in their quantitative response, which depends also on temperature. In suitable areas, individual plants are long-lived (up to 20 years or more). In tropical regions, plants persist for only 1-5 years. Regeneration from seed is usually poor in uncultivated ground. Soil seed reserves are low because plants are rarely allowed to set seed.
Lucerne ecotypes vary considerably, particularly in winter dormancy. Diversity has been increased by natural and artificial hybridization. There are hundreds of cultivars.
Ecology
Lucerne is adapted to temperate and Mediterranean climates and to heavy, neutral or alkaline soils. Suitable cultivars can survive extremely cold winters and hot, dry summers. It is drought-resistant because of its deep root system, but its water use efficiency is poor. It cannot tolerate waterlogging. In the tropics, lucerne is adversely affected by hot, humid conditions which promote several major diseases, by the absence of winter cold and by acid and waterlogged soils.
Agronomy
Lucerne is propagated from seed, at seeding rates of 2-12 kg/ha, sown at a depth of 5-15 mm into cultivated seed-beds, usually in pure stands. Control of existing vegetation is essential. The time of planting varies to suit local conditions. Inoculation of seed with suitable strains of Rhizobium is recommended where lucerne has not previously been grown. It is commonly irrigated and heavily fertilized with P and K fertilizers to enhance forage yield.
Many diseases and insect pests attack lucerne. The most important diseases in the tropics are root and crown rots caused by fungal pathogens such as Phytophthora megasperma and Colletotrichum trifolii. Some cultivars, notably "Trifecta", have improved resistance to these diseases. Plant parasitic nematodes are probably important pathogens in the tropics. The most significant insect pests worldwide are the alfalfa weevil ( Hypera postica ) and several aphid species.
Lucerne is usually cut at intervals of 4-8 weeks while it is growing, but can be grazed provided adequate rest periods are allowed. Defoliation at the early flowering stage is preferable as this coincides with the development of new stems from basal buds. Longevity is reduced under continuous grazing. Frequent cutting is common in the tropics but reduces quantity and stand life.
In parts of the world where lucerne is a major crop, annual DM yields of 10-20 t/ha are obtained. In South-East Asia, lucerne is usually fed green to ruminants. It is a high quality feed but cattle grazing green or freshly cut lucerne may suffer bloat (tympanitis).
Genetic resources and breeding
Significant germplasm collections are held in many countries. The internationally recognized centre for Medicago germplasm is ICARDA (Aleppo, Syria). Other major collections are held by the USDA (Ames, Iowa, United States) and the South Australian Department of Agriculture (Adelaide, Australia). Commercial and government-funded breeding programmes are in progress in many countries. Disease resistance is a key objective.
Prospects
Lucerne will continue to have a minor role in South-East Asia. It will be restricted to suitable soils receiving adequate rainfall in elevated areas. It will have greater use in suitable sites in the subtropics.
Literature
- Hanson, A.A., Barnes, D.K. & Hill, R.R., 1988. Alfalfa and alfalfa improvement. Monograph No 29. Crop Science Society of America, Madison, Wisconsin, United States. 1084 pp.
- Leach, G.J. & Clements, R.J., 1984. Ecology and grazing management of alfalfa pastures in the subtropics. Advances in Agronomy 37: 127-154.
- Lesins, K., 1976. Alfalfa, lucerne. In: Simmonds, N.W. (Editor): Evolution of crop plants. Longman, London. pp. 165-168.
- Lesins, K.A. & Lesins, I., 1979. Genus Medicago (Leguminosae): a taxogenetic study. W. Junk, The Hague, Netherlands. pp. 95-108.
Authors
R.J. Clements
