Crops

Medicago sativa L. - Lucerne, medick

Taxonomic position

Family: Fabaceae Lindl., genus Medicago L., species Medicago sativa L. (Cherepanov, 1995).

Biology and morphology

2n=32. Lucerne is a perennial herbaceous plant. Its root system is very powerful, with a main tap root with ramose lateral roots. Most types of M. varia T. Martyn, sickle medick and wild varieties of perennial lucerne have a root system where the main root is well-pronounced only at the beginning of vegetation. A great number of roots of the same thickness are formed afterwards. Root nodule bacteria develop on the smallest rootlets of lateral roots. They feed at the expense of plant cell plasma and produce nitrous substances from nitrogen in the atmosphere. Some ecotypes of sickle medick, northern hybrid lucerne varieties, etc. form a rhizomatous system or a system of suckers. Lucerne stalks are ramose, bare, tetrahedral, and numerous. They are 50 to 150 cm tall and have 10 to 17 internodes. Lucerne leaves are trifoliolate. Lucerne leaf laminae are obovate or elongated and elliptical, serrated on top. They are often downy on the underside, 1-2.5 cm long and 0.3-1.6 cm wide. The middle tier leaflets are the most typical ones. Lucerne inflorescence is apical. Its panicle raceme is cephaloid or elongated and cylindrical. It is 1.5 to 8 cm long. Lucerne inflorescence consists of a shaft emerging from the leaf axil and 12-26 papilionaceous flowers fixed on short pedicels. Blossoming of lucerne racemes and raceme flowers occurs from the bottom up. Corollae of flowers in different lucerne varieties may be of the same color, or their color may vary greatly. They may be all shades of blue, violet or yellow. More rarely they are white or variegated. Lucerne's fruit is a polyspermous pod. Lucerne pods are small, sickle-shaped or corkscrew-coiled, having one or several coils (up to five). Lucerne seeds are small, reniform, angular, or oval. They are yellow, light brown and grayish brown. 1000 lucerne seeds weigh 1 to 2 g. There are lucerne varieties with a hard seed coat. Scarification (cutting of seed coats in order to increase their permeability) is practiced to increase their germination capacity.

Ecology

Lucerne (M. varia T. Martyn, sickle medick, etc.) belongs to a group of polycarpous plants. Upon fruit-bearing and seed-ripening, the upper shoots die off, while buds and shortened shoots (the crown) in the basal area remain viable and function as renewal organs. New shoots begin to grow in spring or after hay harvest, using plastic substances accumulated by previous shoots. Their branches develop from stalk buds located in main stem axils. Lucerne rosette shape has been determined to correspond to the shape of the bush and, to a certain extent, related to the plants' resistance to unfavorable conditions. Less resistant varieties most often have an erect rosette, while the most resistant varieties have a sprawling rosette. It is almost decumbent and lies close to the ground. Lucerne is a heat-loving plant. It responds well to irrigation. During the period of intensive growth (bud formation and blossoming), drought-resistant lucerne varieties retain much water. Their tissues have a high water-retention capacity. Their transpiration apparatus is very active, and their cytoplasm permeability index is low. Lucerne varieties belonging to Central Russian, Baltic and European ecotypes and lucerne cultivars from India, Syria, Iraq, Brazil, etc. are especially drought-resistant. Wild lucerne populations from Kazakhstan and Central Asia are also highly drought-resistant. Wild local varieties of sickle medick, lucerne, Medicago trautvetteri L., etc. are the most winter hardy. Lucerne has the ability to cross-pollinate; it is an entomophilous plant. The structure of its flower impedes self-pollination and wind-pollination. Lucerne's corolla has 5 petals: the two lower petals are accrete at their bottom, forming a carina; the two side petals form the alae; the upper petal is the vexillum. Inside the closed carina, there is a synema consisting of nine anther filaments accrete at the base. They form a groove with open upper edges and a thin pistil inside. The free tenth stamen is located between the groove.s edges. In a closed flower that is ready for fecundation, the synema in the carina is hard. Its emergence is prevented by the horns of the alae petals near the synema's base, as these horns enter into cavities noticeable from the outside. A domestic honeybee collects nectar at the side of a lucerne flower through a slot between its alae and its vexillum rather than through the corolla's rictus. Only single flowers open (in the field, only 1-3% of flowers open). Their synema hits the neck cavity and squeezes the insect's proboscis. That is why honeybees dislike visiting lucerne's pericarp or collecting nectar from open lucerne flowers. Pollen grains on the lucerne pistil's stigma swell and form the pollen tube. 6-18 ovules form inside the ovary. The number of ripe seeds in a lucerne pod usually does not exceed 2-4, rarely 7-9. The reduction of seed number in lucerne pods is related to the death of embryo sacs prior to pollination and after fecundation. Lucerne pollen is viable for 24 hours at room temperature. In a refrigerator, it is viable for 30 days. Lucerne pollen tubes take 7-9 hours to reach the ovule after pollination. In 5 days' time, the first coil of the pod is formed. Seed ripening sometimes may last 30 days. Under favorable conditions, lucerne blossoms for 20-30 days. Each raceme blossoms for about 10 days. On average, 5 flowers per plant open every day. The lucerne pistil is fertilizable over the course of 3-5 days. Dry, warm and sunny weather is optimal for lucerne flowers to open, for its pollen to germinate and for lucerne-pollinating insects. The best time for flowers to open is between 11 a.m. and 3 p.m. Numerous lucerne flowers have been observed to open simultaneously and easily (auto-tripping) in areas of irrigated agriculture with air temperatures of 38-40°C and a high turgor pressure in the cells of the lucerne flower tissue. Lucerne is genetically self-incompatible. The pollen of the same plant does not germinate or fertilize itself, even though in practically all populations there are some self-fertilizing flowers. Different degrees of depression are usually observed in plant generations born after forced self-pollination. Hay-harvesting techniques during early stages of lucerne vegetation should provide for an additional hay harvest, for the greatest protein collection, for uniform yields of green mass with a relatively high protein content in all hay harvests, for high yields of green mass, and for numerous root residues accumulated after 3 or 4 years of using lucerne grass as fodder. In the early stages of vegetation, lucerne grass should be harvested starting in its 2nd year, since during the first year lucerne plants do not have enough time to form a well-developed root system and to accumulate enough plastic substances in the crown to survive the winter. Harvesting lucerne grass during the first year of its growth leads to its thinning. Besides, the consistent quality of lucerne grass despite multiple yearly hay harvests depends on the timing of the last hay harvest, which should take place at least 30-40 days prior to the end of autumnal vegetation. If necessary, it may take place after stable morning frosts have set in.

Distribution

Lucerne is a cultivated species grown on the 5 continents. The richest natural gene pool of lucerne is concentrated in the three centers of its origin: in Central Asia, in the Levant, and in Europe and Siberia. Its Mediterranean and North American centers of origin are of secondary importance, even though they played an important role in the evolution, breeding and world-wide distribution of cultivated lucerne varieties, especially of M. varia T. Martyn. There is a great number of annual lucerne varieties in Australia. Lucerne cultivation began 7-8 thousand years ago. It was spread by caravans over all of subtropical and moderately warm Eurasia from Eastern Asia to the Mediterranean. It settled in irrigated oases, where it differentiated into regional ecotypes and produced tetraploid varieties. Mutations and breeding with wild varieties contributed to lucerne evolution. Its tetraploid varieties began to prevail. During the age of ancient wars in the East, lucerne was used as fodder. Arabs call lucerne "alfalfa", which means "horse fodder". Arabs introduced lucerne to Spain, from whence it rapidly spread to Italy and Greece. Diploid sickle medick has an enormous natural habitat that spans from 10-80°E and 42-60°N in Eurasia. Lucerne (M. sativa L.) is mostly cultivated on irrigated lands of Central Asia and Transcaucasia. Populations of different varieties of sickle medick (M. falcata L.) are common in arid areas of southeastern Russia, while populations of hybrid varieties are common in the steppe and forest-steppe. In 2004, 4 varieties of sickle medick (Krasnokutskaya 4009, Kubanskaya zholtaya, Pavlovskaya 7, Yakutskaya zholtaya), 11 varieties of lucerne (Artemida, Diana, Kevsala, Yaroslavna, etc.), 57 varieties of M. varia T. Martyn (Vega 87, Voronezhskaya 6, Kameliya, Marusinskaya 425, Pastpishchnaya 88, etc.) were approved for cultivation in the Russian Federation. The main breeding agencies are include the P.P. Lukyanenko Krasnodar Research Institute for Agriculture, the Research Institute for agrarian problems in Khakassia, the All-Union Research Institute for Irrigated Agriculture, the Voronezh Experimental Station for Perennial Herbs, the Krasnoyarsk Research Institute for Agriculture, the Research Institute for Agriculture of the Lower Volga Region, the Kemerovo Research Institute for Agriculture, the V.R. Williams All-Union Research Institute for Fodder, the Siberian Research Institute for Agriculture, the Research Institute for Agriculture of Southeast, the Morshansk breeding station, the Tatarstan Research Institute for Agriculture, and the Urals Research Institute for Agriculture.

Economic value

Lucerne is a valuable fodder plant. It is high in protein with a well-balanced amino-acid composition (on average 20% of dry weight). It is also high in vitamins and minerals, especially calcium. 100 kg of lucerne herbage contains 21.7 fodder units and 4.1 kg of digestible protein. 100 kg of its hay contains 50.2 fodder units and 13.7 kg of digestible protein. Breeding efforts targeted at the reduction of the saponin content of lucerne have been intensified due to the growing use of lucerne meal as protein feed, especially as poultry fodder, and due to the creation of pastures where only lucerne grows. Improvement of digestibility of lucerne-based fodder greatly increases livestock productivity. Its digestibility should be at least 65-70%. The digestibility of vegetable mass may be improved by increasing lucerne stalk digestibility and by reducing stalk cellulose content. Lucerne is used in pastures, as green fodder, hay, grass meal, haylage, and silage. The quality of lucerne fodder and, in particular, of its grass meal depends on its carotin content. If lucerne is harvested in the early stages of its development, it is high enough in carotin, as its leaves contain 5-7 times more carotin than the stalk. Lucerne plants with green stalks contain more carotin than ones with anthocyan-tinged stalks. Lucerne is cultivated as a part of field crop rotation (2-3 years) and fodder crop rotation (up to 5 years). Lucerne is usually sown under the shelter of cereal crops (on irrigated soils, it may be sown without shelter). Lucerne is sown in closed drills. 12-22 kg of Lucerne seeds are sown per hectare. Lucerne seeds are planted at a depth of 2-3 cm in light soils; in heavy clay and loamy soils, they are planted at a depth of 1-2 cm; in irrigated soils, they are planted at a depth of 2-3 cm. After the shelter crop has been harvested, lucerne is additionally fertilized with phosphoric and potash fertilizers. Without irrigation, 2-3 hay harvests are gathered every year. Lucerne yields 40,000 to 50,000 kg of herbage and 8,000 to 10,000 kg of hay per hectare. With irrigation, it yields 4 to 7 hay harvests, 80,000 to 100,000 kg of herbage and 20,000 to 25,000 kg of hay per hectare.

References:

Cherepanov, S.K. 1995. Vascular Plants of Russia and Neighboring Countries. St. Petersburg. pp. 476-479
Konovalov, Y.B., ed. 1990. Individual Breeding of Field Crops. Moscow, pp. 501-512.
State Register Breeding Achievements Approved for Practical Application. 2004. Moscow, pp. 36-37
Zhukovsky, P.M. 1971. Cultivated Plants and Their Congeners. Leningrad, pp. 654-661

© Gashkova I.V.