^kingdom]
AGRICULTURE 203 • crops, especially the clover, much more than the root-crops. live weight of animal within a given time, and for the proThe greater part of the nitrogen of the cereals is, however, duction of a given amount of increase, is, as current food'Sold off the farm; but perhaps not more than 10 or 15 stufis go, measurable more by the amounts they contain of per cent, of that of either the root-crop or the clover (or digestible and available non-nitrogenous constituents than other forage leguminous crop) is sold off in animal increase by the amounts of the digestible and available nitrogenous or in milk. Most of the nitrogen in the straw of the constituents they supply. The non-nitrogenous substance ■ cereals, and a very large proportion of that of the much (the fat) in the increase in live weight of an animal is, at more highly nitrogen-yielding crops, returns to the land as any rate in great part, if not entirely, derived from the manure, for the benefit of future cereal and other crops. non-nitrogenous constituents of the food. Of the nitroAs to the source of the nitrogen of the root-crops—the so- genous compounds in food, on the other hand, only a called “restorative crops”—these are as dependent as any small proportion of the whole consumed is finally stored • crop that is grown on available nitrogen within the soil, up in the increase of the animal—in other words, a very which is generally supplied by the direct application of large amount of nitrogen passes through the body beyond nitrogenous manures, natural or artificial. Under such that which is finally retained in the increase, and so conditions of supply, however, the root-crops, gross feeders remains for manure. Hence it is that the amount of food as they are, and distributing a very large extent of fibrous consumed to produce a given amount of increase in live feeding root within the soil, avail themselves of a much weight, as well as that required for the sustentation of a larger quantity of the nitrogen supplied than the cereal given live weight for a given time, should—provided the crops would do in similar circumstances. This result is food be not abnormally deficient in nitrogenous substance partly due to their period of accumulation and growth —be characteristically dependent on its supplies of digestextending even months after the period of collection by ible and available non-nitrogenous constituents. It has the ripening cereals has terminated, and at the season further been shown that, in the exercise of force by when nitrification within the soil is most active, and the animals, there is a greatly increased expenditure of the accumulation of nitrates in it is the greatest. When a non-nitrogenous constituents of food, but little, if any, of full supply of both mineral constituents and nitrogen is at the nitrogenous. Thus, then, alike for maintenance, for •command, these root-crops assimilate a very large amount increase, and for the exercise of force, the exigencies of of carbon from the atmosphere, and produce, besides the system are characterized more by the demand for the nitrogenous food materials, a very large amount of the digestible non-nitrogenous or more specially respiratory carbohydrate sugar, as respiratory and fat-forming food for and fat-forming constituents than by that for the nitrogenthe live stock of the farm. The still more highly nitro- ous or more specially flesh-forming ones. Hence, as genous leguminous crops, although not characteristically current fattening food-stuffs go—assuming, of course, that benefited by nitrogenous manures, nevertheless contribute they are not abnormally low in the nitrogenous constitumuch more nitrogen to the total produce of the rotation ents—they are, as foods, more valuable in proportion to than any of the other crops comprised in it. It is the their richness in digestible and available non-nitrogenous leguminous fodder crops—especially clover, which has a than to that of their nitrogenous constituents. As, howmuch more extended period of growth, and much wider ever, the manure of the animals of the farm is valuable range of collection within the soil and subsoil, than any of largely in proportion to the nitrogen it contains, there is, the other crops of the rotation—that yield in their produce so far, an advantage in giving a food somewhat rich in the largest amount of nitrogen per acre. Much of this nitrogen, provided it is in other respects a good one, and, is doubtless taken up as nitrate, yet the direct applica- weight for weight, not much more costly. tion of nitrate of soda has comparatively little beneficial In Table XXX., which underwent revision in 1885, and influence on their growth. The nitric acid is most likely was adopted as trustworthy in 1897, is shown the average taken up chiefly as nitrate of lime, but probably as nitrate composition, both per cent, and per ton, of all the leading of potash also, and it is significant that the high nitrogen- cattle-foods. It is obvious that, in the case of almost yielding clover takes up, or at least retains, very little soda. every one of the articles enumerated, individual samples Table XXIX. from Warington’s Chemistry of the Farm may vary even considerably from the average. In foods will serve to illustrate the subjects that have been discussed which are manufactured or imported the percentage of in this section. dry matter is usually high. In those which may be either It is not only the conditions of growth, but the uses to imported or home-grown, the variations in the percentage which the different crops are put, that have to be con- of dry matter in different samples may be comparatively sidered in the case of rotation. Thus the cereal crops, wide, it being as a rule distinctly higher in the imported when grown in rotation, yield more produce for sale in the articles, which could not be shipped unless in a drier conseason of growth than when grown continuously. More- dition than is usual with the home-grown product. In over, the crops alternated with the cereals accumulate very such cases the imported food will probably contain a much more of mineral constituents and of nitrogen in their higher, or the home-grown one a lower, percentage of dry produce than do the cereals themselves. By far the matter than the average given in the table. Hence the greater proportion of those constituents remains in cir- figures as tabulated need to be adopted or modified with culation in the manure of the farm, whilst the remainder judgment, having regard to the influence of the conditions yields highly valuable products for sale in the forms of of growth, maturity, preparation, or preservation to which meat and milk. With a variety of crops, again, the the foods have been subject. Unless, however, the variamechanical operations of the farm, involving horse and tion from the standard composition adopted in the table hand labour, are better distributed over the year, and are be more than usual, the effect on the estimates of the therefore more economically performed. The opportunities manure value—for which the table is primarily intended— which rotation cropping affords for the cleaning of the will not be material, though it will obviously be much land from weeds is another distinct element of advantage. greater in the case of the nitrogen than in that of either the phosphoric acid or the potash. The table is useful for The Feeding of Animals, and the Manurial Value purposes of comparison—for example, one ton of decorof Different Foods. ticated cotton cake contains about four times as much In the feeding experiments at Rothamsted it has been nitrogen as a ton of maize, wheat, or barley, and thirty shown that the amount of food consumed, both for a given | times as much as a ton of mangel wurzels.
