CLOVER, the English name for plants belonging to the genus Tri f olium, so-called from the leaf, which has three leaflets (tri foliate). It is a member of the family Leguminosae, and contains about 30o species, found chiefly in north temperate regions, but also, like other north temperate genera on the mountains in the tropics. The plants are small annual or perennial herbs with tri foliate (rarely 5- or 7-foliate) leaves with stipules adnate to the leaf-stalk, and heads or dense spikes of small red, purple, white or rarely yellow flowers; the small few-seeded pods are enclosed in the calyx. Twenty species are native in Britain, and several are extensively cultivated as fodder-plants. T. pratense, red or purple clover, of which there are a number of varieties, is the most widely cultivated. T. incarnatum, crimson or Italian clover, though rather tender, is a most valuable forage crop in the warmer parts of England. T. repens, white or Dutch clover, is a perennial abundant in meadows and good pastures. The flowers are white or pinkish, becoming brown and deflexed as the corolla fades. There are a number of commercial varieties, e.g., wild white, culti vated white and mammoth. T. hybridum, alsike or Swedish clover is a perennial which was introduced from Sweden in and has now become naturalized in Britain. The flowers are pale pink or white and resemble those of the last species. T. medium, zig-zag clover, a perennial with straggling flexuous stems and rose purple flowers, is not met with in commerce. T. minus, common in pastures and roadsides, with smaller heads and small yellow flowers, turning dark brown, is the shamrock. Nearly all the fore going have become very widely naturalized in the United States and Canada. Specimens of shamrock and other clovers are not infrequently found with four leaflets and, like other rarities, are considered lucky.
Cultivation.—Clover was originally introduced from Flanders into England as a farm crop about the middle of the 17th cen tury by Sir Richard Weston. He is distinguished in the annals of agriculture as being the first to introduce into England the rotation of crops based on roots and clover, although it was not until a century later that the new system was adopted on any wide scale. Clover is grown as a farm crop in all parts of Great Britain and occupies about one-fourth of the total arable area. It is frequently sown 'With rye-grass or other green crops and appears in the agricultural returns under the heading of "clover and rota tion grasses." There are several kinds of clover in common agricultural use, including white, or Dutch clover, red or broad clover, alsike and Trifolium incarnatum. White clover is indigenous and is found in most good pastures, especially on rich land containing lime. It has a creeping habit—hence its botanical name Trifolium re pens—and is usually eaten off by sheep, as it is not profitable to mow it. In recent years "wild white clover" has come into much favour. Broad or red clover is known also as purple clover and is probably more widely grown than any other kind. It is com monly cut for hay but, like the white clover, is also folded with sheep. It will stand for two or three years, or even more, but is specially susceptible to "clover sickness," a disease caused by minute organisms in the stem of the plant. When land becomes "clover sick" it usually requires some years to recover before it can successfully grow the crop again. Trifolium, although a name properly applicable to all kinds of clover, has been appropriated by farmers to that handsome and easily recognizable kind which bears large dark crimson flowers (T. incarnatum) . This is often taken as a catch crop, sown on the stubbles and fed off in May or June. Cow grass is a variety of red clover which, although some what slower in growth, is more lasting and is less liable to clover sickness. It is well adapted for a mixture of "seeds" intended to remain down for some time.
In the strict four-course rotation clover, or "seeds," stand only for one year, but it has long been the practice with many farmers to leave the crop for two or more years, or by sowing with suit able mixtures to let it remain for several years as a temporary pasture. (See GRASS AND GRASSLAND.) (X.) The economically valuable clovers in America are all traceable to European origin. No native species has been cultivated. The cultivated clovers are red (Trifolium pratense), alsike (T. hybridurn), crimson (T. incarnatum), and white (T. repens). Besides these, subterranean clover (T. subterraneum) and straw berry clover (T. f ragif erum) have been introduced to a limited extent from Australia, where they assume considerable im portance as grazing plants.
Clover Culture.—Red and alsike clover occupy practically the same place in American agriculture and are treated together in crop statistics. The chief clover region in America is the area from the western border of Minnesota, Iowa and Missouri and the southern border of Missouri, Tennessee and North Carolina, east and north into Canada. Red and alsike clovers are commonly seeded with timothy, sometimes alone. In the north-eastern quar ter of the United States more than 52% of the hay acreage con tains clover and it is therefore the most important legume in this part of the United States. Seeding of red and alsike clover is commonly done with a "nurse" crop of small grain and no harvest is taken during the seeding year. The next year the first crop is cut for hay and the second may be cut for hay, or for seed, or it may be turned under for soil improvement.
Clover Failure.—What is called clover sickness in Great Britain, does not occur in the United States except to a lim ited extent in western Oregon, although the disease is occasion ally serious on crimson clover on the Atlantic sea board. The failure of clover to make a stand or to give a satisfactory yield is, however, not uncommon. The causes are lack of lime, phosphor ous or potash and lack of organic matter. These deficiencies are in most cases due to poor farming methods, such as prolonged culti vation without adequate rotations. Another common cause of failure is the use of the seed of non-adapted strains.
Varieties and Strains.—There are in use in America two varieties, the early or June red and the mammoth. These are re spectively comparable to, but not the same as, the English double cut and single-cut clovers. The American clover has spreading hairs, while the Europear clovers are smooth or have appressed hairs. For conditions in the United States, no imported clovers are so well adapted as the American type. Some European clovers, as the Italian, are quite unsuited to American conditions, while French and Russian may be used in some sections but not in others. French clover is not cold-resistant enough for regions with severe winters and all European clovers are more susceptible to disease and to insect injury in the United States than the American clover. An exception occurs in the case of clover mildew, to which the American clover is more susceptible than the European. One of the chief factors in clover failure during recent years has been the large importations of seed of European strains. Su& importations have averaged about 12,000,00o lb. per year. (For further information on clover failure the reader is referred to publications of the U.S. Department of Agriculture and State agricultural experiment stations.) Other Clovers.—White clover is used as a pasture plant every where save in the semi-arid regions. It is seldom seeded but comes up naturally. The mammoth white clover of England is called Ladino in America and is successful in the irrigated regions of the West. The wild white, so highly regarded in Britain, is of no special value in the United States. Crimson clover is used mainly on the Atlantic seaboard from New Jersey south as a soil improving crop.
The hop clovers have been introduced from Europe and one of them, the least hop clover, the true shamrock, has become of some importance as a pasture plant in Louisiana and Arkansas. Other so-called clovers are sweet clover and Japan clover or Lespedeza, a valuable pasture plant throughout the South which was introduced from Japan some time before 1856, and has spread naturally from southern Indiana to the gulf and as far west as eastern Kansas.
Seed Production.—Red clover seed is produced over most of the main clover area and in the irrigated region of the West. It is commonly taken from the second crop. Alsike clover seed is produced in the same region as red, but is taken from the first crop, since this species does not commonly produce two cuttings in a season. White clover seed is produced chiefly in Wisconsin and Louisiana, although small amounts are harvested elsewhere. Crimson clover seed for the trade is produced in small amounts in Delaware, Maryland and Tennessee, but is frequently har vested for home use in other sections.
Native Clovers.—There are upwards of 5o native species of clover on the Pacific coast (35 occurring in California) and in the Rocky mountain region, but east of the Mississippi river only four native species occur. See GRASS AND GRASSLAND.
(A. J. Pi.)