It is little more than a century since clovers were introduced into fleld.culture in Britain. They are now universally cultivated on large farms in alternation with grain crops. The kinds most generally sown are the common red, cow-grass, Dutch white, yel low, and aisike. The common red is the finest and most valuable, but it is difficult to grow unless on naturally rich soils. In America it grows well on sandy loams, though sown every alternate year on the same land. But in Britain the land is thought to become " clover-sick" when sown too frequently with this crop. An interval of not less than eight years is thought advisable. From 0 to 20 lbs. of seed per acre is the quantity sown. Red C. is most esteemed for being mixed with rye-grass for the making of hay. When it grows well, it bears to be cut more than once a year. Coic-grass much resembles the common red C. It is coarser but hardier, and better suited for pasture, as it bears more herbage, and comes better up after being eaten close down by stock. Dutch white C. is only esteemed for pasture; it grows short and thick on the ground, but throws out fresh stems and flowers during the most of the growing season. In the s. of England, it is sometimes sown with but little rye-grass seed along with it; in Scotland, as much as a bushel or a bushel and a half of rye-grass is mixed with it for pasture. Yellow C. is chiefly sown on ground where neither the white nor red grows freely. It is not sown so frequently as it probably ought to be, for it rises early in spring, and a mixture of it with other clovers forms good pasture on all grounds. Alsike C. has been recently introduced: it rises much higher than white C., and offers to be a useful addition to our pasture-plants. Land must be thoroughly cleaned of perennial weeds before it is sown with C., as the
land cannot be subjected to cultivation while it is under this plant; C., therefore. is always sown in the end of the rotation, or as near the fallow or turnip crop as possible. It is sown early in spring among the winter-wheat, or with the barley crop, and slightly harrowed in; for the seeds being small are not difficult to bury. Farm-yard manure is as good as any for clovers. A well-manured soil greatly assists in keeping the plants from dying out in spring. Clovers. like grasses, play a most important part in restoring fertility to land which has been exhausted by grain-crops.. Their leaves gather food— carbonic acid and ammonia—from the atmosphere, which they store up in their roots and stems; and these, on decomposing, afford food for eel cals or other crops which are more dependent on a supply within the soil.
The caterpillars of a number of species of moth feed on the leaves of different kinds of C.; but time insects most injurious to the C. crops are weevils of the genera apion and Sitorsa. See CLOVE1I-WEEVIL and PEA-WEEVIL.
Apion, a genus of small pear-shaped weevils (coleopterans insects, section tetramera, family rhynchophora), different species of which feed on the leaves, and their !arm on, the seeds of .clover, some also on those of tares and other leguminous plants. Like the other weevils, the perfect insect has the head very much elongated into a sort of muzzle. A. apricans often does much injury to fields of com mon red clover, particularly interfering with the production of seed. It lays its eggs among the flowers, and the little grubs eat their way through the calyx into the pod. It is of a bluish-black color, little more than a line long. A. Itacipes is attached in like man ner to white clover, and other species of clover have their particular weevils.