If it be granted that the crops above stated are fair average returns from the same quality of land—that the acre, for example, which produces 25 bushels of wheat, will also produce 10 tons of potatoes, and so on—then it appears that the land which, by cropping with wheat, would yield a given weight of starch, would, when cropped with barley or oats, yield one-half more, with Indian corn or potatoes about three times as much, and with turnips five times the same quantity. In other words, the piece of ground which, when sown with wheat, will maintain one man, would support one and a half if sown with barley or oats, three with Indian corn or potatoes, and five with turnips—in so far as the nutritive power of these crops depends upon the starch and sugar they contain.
Again, if we compare the relative quantities of gluten, we see that wheat, beans, and Indian corn yield, from the same breadth of land, nearly an equal quantity of this kind of nourishment—potatoes one-third less, and barley and oats only one-third of the quantity—while turnips yield four times as much as either wheat, beans, or Indian corn.
On whichever of these two substances, therefore, the starch or the gluten, we consider the nutritive property of the above kind of food to depend, it appears that the turnip is by far the most nutritive crop we can raise. It is by no means the most nutritive weight for weight, but the largeness of the crop (25 tons) affords us from the same field a much greater weight of food than can be reaped in the form of any of the other crops here mentioned.
In this the practical farmer will see the peculiar adaptation of the turnip husbandry to the rearing and fattening of stock. Could the turnip be made an agreeable article of general human consumption, the produce of the land might be made to sustain a much larger population than under any other of the above kinds of cropping.
The relative nourishing power or value as food of different vegetable substances, is supposed by some to depend entirely upon the relative proportions of gluten they contain. According to this view, the pea and the bean are much more nourishing, weight for weight, even than wheat, and this latter grain, than any of the other substances mentioned in the above table. Thus, 56 lbs. of beans would afford as much sustenance to an animal as 67 of pease, 100 of wheat-flour, or 177 of rice.
In order to understand the value of this opinion, it will be proper to consider the several purposes which the food is destined to serve in the animal economy—what the animal must derive from its food to maintain its existing condition, or to admit of a healthy increase of bulk.
SECTION V.—OF THE FEEDING OF ANIMALS,
AND THE PURPOSES SERVED BY
THE FOOD THEY CONSUME.
The food of plants we have seen to consist essentially of two kinds, the organic and the inorganic, both of which we have insisted upon as equally necessary to the living vegetable—equally indispensable to its healthy growth. A brief glance at the purposes served by plants in the feeding of animals, will not only confirm this view, but will also throw some additional light upon the kind of inorganic food which the plants must be able to procure, in order that they may be fitted to fulfil their assigned purpose in the economy of nature.
Man, and all domestic animals, may be supported, may even be fattened, upon vegetable food alone: vegetables, therefore, must contain all the substances which are necessary to build up the several parts of animal bodies, and to supply the waste attendant upon the performance of the necessary functions of animal life. Let us consider what these substances are, and in what quantities they must be supplied to the human body.
1. The food must supply carbon for respiration.