Rotation of Crops.

Rotation of Crops. In successful tillage-farming it is a fundamental principle that the various crops shall be grown in a well-considered rotation. There are solid reasons for this. The plants, like the animals, of the farm differ much in their habits and in the different sorts of food upon which they subsist. Although all plants tend to exhaust the soil, they do so in widely different degrees; they withdraw from the soil different kinds and quantities of ingredients. Some of the farm crops have long, penetrating roots, which draw nourishment from the deeper layers of the soil; others have short or spreading roots, which ramify near the surface. Certain crops occupy the ground for a much longer period than others; some encourage the growth of weeds or interfere with the proper cleaning of the land; others facilitate the work of eradicating weeds; and finally, the 'crop residues' of the various plants of the farm differ greatly. A glance at the following figures, giving the average weight of the principal ingredients removed (per acre in lbs.) from the soil by the leading farm crops, will show the importance of growing these crops upon a carefully-considered system of rotation.

It is thus obvious that by alternating the root, the cereal, and the grass and clover crops the producing power of the soil is more easily maintained, and its exhaustion longer deferred. With the fuller knowledge which is now available both as to the wants of the plants and the means of supplying these wants, it is possible, and in certain cases also practicable, for the farmer to grow with success the same kind of crop on the same land year after year for almost any length of time. A more economical method, however, is to alternate the crops, so that the natural resources of the soil and the repairing influences incident to a judicious rotation may be utilised to full advantage. It was long ago demonstrated in practice that when land lies for a few years under grass and clover it becomes enriched with ash constituents and nitrogen. The grasses and clovers not only increase the quantity of nitrogen in the surface soil by drawing supplies of it from the subsoil and from the atmosphere, but they have also the power of conserving that accumulated nitrogen in a form in which it is easily made available to a crop of grain. Points often insufficiently considered in tillage-farming are the period of growth and the season of the year during which the crop occupies the ground. Judging from the table given above, one would imagine that turnips would require in the form of manure far more nitrogen than is required for wheat. In practice, however, it is well known that exactly the reverse is the case. The difference in the points just mentioned, that is in the period and season of the growth of the two crops, is responsible for this important peculiarity. Nitrification (q.v.), or the formation of nitrates in the soil, is most active during summer and autumn, and the cereal crops thus occupy the ground at the time when the soil is comparatively deficient in nitrates. The root-crop on the other hand is in full growth in the autumn, when the supply of nitrates in the soil is at the maximum. Root-crops consumed on the farm are therefore a good preparation for succeeding crops of cereals. The precise form of rotation most suitable for particular farms varies greatly, depending upon various circumstances, and especially the nature of the soil, climate, markets, available supplies of extra manures, amount of live-stock kept, &c. That course of cropping is evidently the most desirable which will economically secure, with thorough cleanliness of the soil, a high and increasing state of fertility.

Many rotations are based 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) turnips, swedes, mangolds, potatoes, or bare fallow; (4) barley. The details of this system 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 racks by sheep, which on most highly cultivated farms receive besides a daily allowance of cake or corn. In districts where the 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 ploughed up in autumn, and followed generally in England by wheat, and in Scotland by oats. These crops are now often drilled, to admit of horse and hand hoeing. After harvest the stubble is, if possible, cleaned by the scarifier, grubber, or plough and harrows; or, where the management for several years has been good, any patches of couch-grass or other weeds are best forked out by hand. The land, especially if heavy, or intended for mangolds drilled on the flat, as practised in the drier parts of England, may then be manured and deeply ploughed: the grubber and harrows, in April or May, suffice to prepare for the drilling of mangolds or swedes. Heavy land, intended either for roots or barley, should, in spring, be 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 underneath the plant. Frequent horse and hand hoeings should ensure the thorough cleaning of the crop. Unless in the neighbourhood of towns, where it is greatly more profitable to sell off the whole of the root-crop, part of the swede or mangold crop is taken home for the cattle, and the remainder consumed by sheep in the field. After the fallow or cleaning crop another cereal 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 worse 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 be 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.

The Norfolk four-course system is unsuitable for heavy land, where a large breadth of roots cannot be profitably grown, and where their place, as a cleaning crop, is taken by bare fallow, vetches, or pulse. Bare fallows are, however, much less frequent than formerly, being now confined to the most refractory of clays, or to subjects that are so hopelessly full of weeds as to require for their extirpation several weeks of summer weather, and the repeated use of the steam or horse ploughs, the scarifier, grubber, and harrows. In such circumstances winter vetches are often put in during September or October, are eaten off by sheep and horses in June or July, and the land afterwards cleaned: this practice is extensively pursued on the heavier lands in the midland and southern counties of England. In such localities the following system is approved of: (1) The clover leas are seeded with (2) wheat; then come (3) beans, pulse, or vetches, manured, horse or hand hoed; (4) on good land wheat succeeds; (5) oats or barley often follow, but, to prevent undue exhaustion of plant-food, this system requires considerable outlay in artificial manures, cake, and corn; (6) a fallow, or fallow crop, deeply and thoroughly cultivated, and well manured, comes to restore cleanliness and fertility; (7) barley or wheat is drilled, and amongst this the clover-seeds are sown. On the heavier carse-lands in Scotland the following plan of cropping is practised: (1) Clover; (2) oats; (3) beans; (4) wheat; (5) root-crop, usually including a considerable breadth of potatoes; (6) wheat; (7) barley, with which the clovers or mixed grasses are sown. Under this system it is difficult, with so few cleaning crops, to keep the land clean; roots, besides, are not produced in quantities sufficient properly to supply either cattle or sheep during the winter. To remedy these defects roots may be introduced after the oats, and would be followed either by wheat or barley. This extends the rotation from seven to nine years.

In most well-cultivated districts, whether of heavy or light land, stock-farming is extending, and a more vigorous effort is being made to raise the fertility of the land. Root-crops are accordingly more largely grown; indeed, it is sometimes found profitable to grow two root-crops consecutively; thus, after turnips, swedes, cabbages, or mangolds, well manured from the town or farmyard, and eaten off by sheep, potatoes of superior quality are produced with one ploughing and a dose of portable manure. Specialities of management occur in almost every locality. Near London, and in other southern districts, early potatoes or peas are grown for market, and are immediately followed by turnips. In many parts of England, where the soil and climate are good, rye or vetches sown in autumn are consumed in early summer, and a root-crop then put in.

Good rotations do not necessarily ensure good farming; they are merely means to an end. And as agricultural education and enterprise extend fixed rotations will be less regarded. The market-gardener, who extracts a great deal more from his land than the farmer has hitherto been able to do, does not adhere to any definite system of cropping. If the farm is kept clean and in improving condition there can be no harm in growing whatever crops it is adapted to produce. Cropping clauses are requisite during only the three or four last years of a tenancy. The restrictions found in some agreements, preventing the growth of clover for seed, flax, and even potatoes, are inadmissible. Equally objectionable are clauses against the sale of particular sorts of produce, such as hay or roots. The farmer, if he is fit to be entrusted with the use of the land, ought to be permitted to grow or sell off any crop he pleases, provided an equivalent in manure be brought back. On well-cultivated land, in good condition, it is now the practice of the best farmers to take oats or barley after wheat; indeed, some of the best malting barley in Essex, on the Scottish carse-lands, and elsewhere is now grown after wheat. The frequent growth of cereals, and the heaviest of hay and root crops, even when removed from the farm, may be fairly compensated for by judicious and liberal treatment with town-dung, sewage, or artificial manures. The plant-food disposed of in the more ordinary sales of the farm is economically restored by the use of bones or superphosphate, guano, or nitrate of soda, or by keeping plenty of stock on the farm, and supplying them liberally with cake and corn. See also the articles AGRICULTURE, FALLOW, MANURE, SOILS, and those on the various crops.