IX. SUCCESSION OF CROPS
There are few agricultural facts more fully ascertained than this, that the growth, year after year, on the same soil, of one kind of plants, or family of plants, and the removal from it, either of the entire produce, or at least of the ripened seeds of such plants, rapidly impairs the general fertility of that soil, and, in particular cases, unfits it for bearing further crops of the kind by which it has been exhausted. The explanation of the causes of this phenomenon belongs to the agricultural chemist or vegetable physiologist, to whom we willingly leave the task. What we have to do with is the fact itself, and its important bearing on agricultural practice. There is no natural tendency in the soil to deterioration. If at nay time, therefore, the earth hails to yield its increase for the use of man, it is owing to his own ignorance and cupidity, and not any defect in the beneficent arrangements of the Creator. The aim, then, of the agriculturist, and the test of his skill, is to obtain from his farm abundant crops at a remunerative cost, and without impairing its future productiveness. In order to this, tow conditions are indispensable, -- first, that the elements of fertility abstracted from the soil by the crops removed from, it be duly and adequately restored; and second, that it be kept free from weeds. The cereal grains, whose seeds constitute the staple food of the human family, are necessarily the most important and valuable of our ordinary crops. The stated removal from a farm of the grain produced on it, and its consumption elsewhere, is too severe a drain upon its production powers to admit of these crops being grown every year on the whole, or greater part of it, without speedily impairing its fertility. Supposing, however, that this waste could be at once repaired by the annual return to the soil of manure equivalent in constituent elements to the produce removed, the length of time which grain-crops occupy the soil, and their habit of growth, interpose peculiar difficulties in the way of cleaning it thoroughly, either before they are sown, or while they occupy the ground. Again, although bread-corn is the most important product of our soil, other commodities, such as butcher-meat, dairy produce, vegetables, wool, and flax, are indispensably required. The economical culture of the soil demands the employment of animal power, which, to be profitably used, must be so distributed as to fill up the year. The maintenance of the working cattle, and of other live stock, implies the stated culture of a large amount of herbage and forage. Now, these varied conditions are duly met by cultivating grain and cattle crops alternatively, and in about equal proportions, In carrying out these general principles, much discrimination is required in selecting the particular plants best adapted to the soil, climate, and other circumstances, of each farm, and in arranging then in the most profitable sequences; for not only is it necessary duly to alternate grain and green crops, but in general, there is a necessity, or at least a high expediency, in so varying the species or varieties of the latter class as to prolong, as much as possible, the periodic recurrence of any one of them on the same field. In settling upon a scheme of cropping for any particular farm, regard must be had its capabilities to the markets available for the disposal of its products, and to the command of manure. When these things have been maturely considered, it is always beneficial to conduct the cropping of a farm upon a settled scheme, The number of men and horses required to work it is regulated chiefly by the extent of the fallow-break, which it is therefore desirable to keep as near to an average annual breadth as possible. When the lands of a farm vary much --- as regards fertility, fitness for particular crops, and proximity to the homestead, --- they must be so apportioned as to make the divisions allotted to each of crops as equal as possible in all respects, taking one year with another. Unless this is done, those fluctuations in the gross produce of farms which arise from varying seasons are needlessly, it may happen ruinously, aggravated; or such an accumulation of labour is thrown on certain years which may prove unfavourable ones as to weather, that the work is neither done well nor in due season.
No better rotation has yet been devised for friable soils of fair quality than the well-known four-field or Norfolk system. By this course half the arable lands are in grain crops, and half in cattle-crops, annually. It is indeed true that, in the way in which this course has hitherto been usually worked, both turnips and clover have recurred so frequently (every-fourth year) on the same fields, that they have become subject to disease, and their produce excessively precarious, But the excellence of this course is, that its main features can be retained, and yet endless variation be introduced in its details. For example, instead of a rigid one-fourth of the land being each year under turnips, barley, clover, and wheat or oats, respectively, half only of the barley division is frequently in practice now sown with clover seeds, and the other half cropped in the following years with beans, peas, potatoes, or vetches. On the same set of fields, coming round again to the same point, the treatment is reversed by the beans, &c., and clover, being made to change places. An interval of eight years is thus substituted for one of four, so far as these two crops are concerned. Italian rye-grass, unmixed with any other plant, is now frequently taken in lien of clover on part of the division usually allocated to it, and proves a grateful change both to the land and to the animals which consume it. In like manner, instead of sowing turnips unvarying every fourth year on each field, a portion of the annual division allotted to this crops can advantageously be cropped with mangel-wurzle, carrots, or cabbages, care being taken to change the site occupied by each when the same fields again come in turn. The same end is even so far gained by alternating Swedish with yellow or globe turnips. It is also found expedient, either systematically or occasionally, to sow a field with clover and pasture grasses immediately after turnips, without a grain crop, and to allow it to remain in pasture for four years. A corresponding extent of the other land is meanwhile kept in tillage, and to grain crops in succession are taken on a requite portion to equalize the main divisions, both as respects amount of labour and the different staple products. A closer cover of grasses and a better pasture is obtained in this way than by first taking the customary grain crop after turnips; the land is rested and invigorated for future tillage, the outlay on clover and grass-seeds somewhat diminished, and the land better managed for the interest of all concerned than by a rigid adherence to the customary rotation.
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