ROTATION OF CROPS. The plants, like the animals of the farm, differ much in their habits, and in the different sorts of food on which they subsist. The broad-leafed clovers, turnips, and mangold abstract from the air a large proportion of the materials of their growth; whilst the narrower-leafed grains and grasses, especially if their seeds are ripened, partake more largely of mineral food withdrawn from the soil. The cereals require for their healthy nutrition large supplies of phosphoric acid and silica; legumi nous plants devour a large share of lime; turnips, carrots, and clo'ver take up a great amount of potash. Corn-crops. occupying the ground during the greater part of the year, favor the growth of weeds; well-tended root-crops, on the other hand, afford better opportunity for deep culture, for the extirpation of weeds, for the convenient applica tion of manures; whilst, being in great part consumed on the land, they raise its fertility. Mainly from such considerations, the farmer of arable land is led to grow a succession of dissimilar plants, or, in other words, to adopt a rotation of crops. The cereals exhaust ing the farm, on account of their ripened seeds being sold off, are generally alternated with fallow, root, or cleansing crops, or with beans and peas, which occupy a kind of intermediate position between the cereals and the roots; while clovers or grasses are taken at intervals of six or eight years. The rotation most suitable for a particular farm is, however, greatly modified byvarious circumstances, and especially by the nature of the soil, climate, markets, available supplies of extra manures, amount of live stock kept, etc. That course of cropping is evidently the most desirable which'•will economi cally secure, with thorough cleanness of the soli, a high and increasing state of fertility.
Many rotations are hosed upon the Norfolk or four-course system, which consists of (1) Clover or mixed grass seeds; (2) Wheat, or in Many parts of Scotland, oats; (3) Tur nips, Swedes, mangold, potatoes, or bare fallow; (4) Barley. The details of this sys tem are generally as follows: The clovers or grasses are mown or grazed; when cut, they are either used green or are dried for hay; the second crop is carted home for the cattle or horses; near towns, it is sold off; or it is consumed on the ground in rack's by sheep, which on most highly cultivated farms receive besides a daily allowance of cake or corn. In districts where town-manure can be obtained, a top dressing is applied as
soon as the first crop of grass is cut. On the poor and worse cultivated soils, the grass crop occasionally remains down for two, or even three years, thus extending a four into a five or six years' rotation. The clovers or mixed seeds are plowed up in autumn, and followed generally in England by wheat, and in Scotland by oats. These crops are now usually drilled, to admit of horse and hand hoeing. After harvest, the stubble is, if pos sible, cleaned by the scarifier, grubber, or plow and harrows; or, where the manage ment for several years has been good, any patches of couch-grass or other weeds are best forked out by band. The land, especially if heavy, or intended for mangold drilled on the flat, as practiced in the drier parts of England, may then be manured and deeply plowed the grubber and harrows, in April or May, suffice to prepare for the drilling of mangold or Swedes. Heavy land, intended either for roots or barley, should it] spring be plowed or disturbed as little as possible. In Scotland, and the cooler moist climates of the north and west of England, turnips and potatoes are grown on raised drills or balks, in which the manure lies immediately underner.th the plant. Frequent horse and hand hoeings should insure the thorough cleaning of tile crop. Unless in the neighborhood of towns, where it is greatly more profitable to sell off the whole of the root-crop, part of the Swedes or mangold is taken home for the cattle, but the largest por tion is consumed by sheep in the field. After the fallow or cleaning crop, another cereel crop is grown: under the Norfolk system, this is generally barley, with which the clovers or seeds are sown out. Where sewage or tank water is available, Italian rye grass is often used, and on land in high condition, early large and repeated cuttings are obtained; but rye-grass has the disadvantage of being a wrsoe preparation than clover for the wheat-crop which usually follows. The chief failing of the four-course system consists in the frequent recurrence of clover, which cannot he successfully grown oftener than once in six or eight years. To obviate this difficulty, one-half of the clover quarter' is now often put under beans, peas, or vetches, thus keeping the grass or clover seeds eight years apart.