The Products of Vegetation—Importance of
_Chemical_ quality as well as quantity of
Produce—Influence of different Manures on the
quantity and quality of the Crop—Influence of the
time of Cutting—Absolute quantity of Food yielded
by different Crops—Principles on which the Feeding
of Animals depends—Theoretical and experimental
value of different kinds of Food for Feeding
Stock—Concluding Observations.
The first object of the practical farmer is, to reap from his land the
largest possible return of the most valuable crops, without permanently
exhausting the soil. With this view he adopts one or other of the
methods of treatment above adverted to, by which either the physical
condition or the chemical constitution of the soil is altered for
the better. It may be useful to shew how very much both the quantity
and the quality of a crop is dependent upon the mode in which it is
cultivated and reaped, and how much control, therefore, the skilful
agriculturist really possesses over the ordinary productions of nature.
SECTION I.—OF THE INFLUENCE OF MANURE ON THE QUANTITY OF THE WHEAT AND
OTHER CORN CROPS.
Every one knows that some soils naturally produce much larger returns
of wheat, oats, and barley than others do, and that the same soil will
produce more or less according to the mode in which the land has been
prepared by manure, or otherwise, for the reception of the seed. The
following table shews the effect produced upon the quantity of the crop
by _equal quantities_ of different manures applied to the _same soil_,
sown with an equal quantity of the same seed.
Return in bushels from each
Manure applied. bushel of seed.
Wheat. Barley. Oats. Rye.
Blood, 14 16 12½ 14
Night-soil, — 13 14½ 13½
Sheep’s dung, 12 16 14 13
Horse dung, 10 13 14 11
Pigeon’s dung, — 10 12 9
Cow dung, 7 11 16 9
Vegetable matter, 3 7 13 6
Without manure, — 4 5 4
It is probable that on different soils the returns obtained by the use
of these several manures may not be always in the same order, yet,
generally speaking, it will always be found that blood, night-soil, and
sheep, horse, and pigeon’s dung, are among the most enriching manures
that can be employed.
We have already seen a theoretical reason for believing that night-soil
should be among the most enriching manures, and the result of actual
trial here shews that it is one of the most practically valuable which
the farmer can employ.
Two other facts will strike the practical man on looking at the above
table.
1. That exclusive of blood, sheep’s dung gave the greatest increase in
the barley crop. The favourite Norfolk system of eating off turnips
with sheep previous to barley, besides other benefits which are known
to attend the practice, may owe part of its acknowledged utility to
this powerful action of sheep’s dung upon the barley crop.
2. The action of cow dung upon oats is equally striking, and the
large return obtained by the use of vegetable manure alone—thirteen
fold—may perhaps explain why in poorly farmed districts oats should be
a favourite and comparatively profitable crop, and why they may be
cultivated with a certain degree of success on lands to which no rich
manure is ever added.
SECTION II.—INFLUENCE OF THE KIND OF MANURE ON THE CHEMICAL QUALITY OF
THE GRAIN.
But the quality of the grain also, as well as its quantity, is
materially affected by the kind of manure by which its growth is
assisted. The apparent quality of wheat and oats is very various; but
in samples apparently equal in quality, important chemical differences
may exist, by which it is believed that the nourishing properties of
the grain are materially affected.
It has been stated in a previous chapter (p. 43), that when flour is
made into dough, and this dough is washed upon a linen cloth with water
as long as the latter passes through milky,—the flour is separated into
_starch_, which subsides from the water, and _gluten_, which remains
behind. The quantity of gluten thus left varies more or less with
almost every sample of flour, and the nutritive properties of each
sample are supposed to depend very much upon the quantity of gluten it
contains. So far it seems to be pretty well ascertained, that those
varieties of grain which contain the largest amount of gluten yield
also the greatest return of flour, and the heaviest weight of bread.
The weight of gluten contained in 100 lbs. of dry wheat has been found
to vary from 8 to 34 lbs., and this proportion is affected in a very
remarkable manner by the kind of manure which has been applied to the
land. Thus the proportions of starch and gluten in 100 lbs. of the
grain of the same wheat, grown on the same land, differently manured,
was as follows:—
Manure. Starch. Gluten.
Blood, 41 lbs. 34 lbs.
Sheep’s dung, 42 ” 33 ”
Horse dung, 62 ” 14 ”
Cow dung, 62 ” 12 ”
Vegetable manure, 66 ” 10 ”
Potato-flour, which consists entirely of starch, makes a fine light
bread, easily raised. Wheaten-flour, which contains little gluten,
approaches in this respect to potato-flour. When the quantity of gluten
is large, greater care is required to make a good light bread; but
the bread from such flour is generally found to be more nutritive in
its quality. A dough peculiarly rich in gluten is required for the
manufacture of macaroni and vermicelli; such is said to be the flour
naturally produced in southern Italy. By the above table it appears,
that the use of richer animal, or poorer vegetable manures, would
enable the farmer to raise, at his pleasure, either a rich macaroni
wheat, or one poor in gluten suited for the makers of fancy bread.
An equally striking effect is not produced upon other kinds of grain by
varying the manure. Thus the proportions of starch and gluten in the
dry grain of barley and oats, differently manured, were found to be as
follows:—
BARLEY. OATS.
Starch. Gluten. Starch. Gluten.
Blood, 66½ 6½ 60 5½
Night-soil, 66 6½ 60 5
Sheep dung, 66½ 6½ 61 4½
Horse dung, 66 6½ 61½ 4½
Cow dung, 69 3½ 62 3½
Vegetable manure, 69 3 66½ 2¼
Unmanured, 69½ 3 66½ 2¼
Though a variation in the proportion of gluten can be observed in both
of these kinds of grain, according as one or other of the above kinds
of manure was employed, yet neither the average quantity of gluten
present in them, nor the variations to which the quantity is liable,
are at all equal in amount to what are observed in the case of wheat.
The malting of barley is known to be affected by a variety of
circumstances. It should be so uniform in ripeness as to sprout
uniformly, so that no part of it should be beginning to shoot when
the rest has already germinated sufficiently for the maker’s purpose.
On this perfect sprouting of the _whole_ depends in some degree the
swelling of the malt, which is of considerable consequence to the
manufacturer.
But the _melting_ quality of the grain, which is of more consequence
to the brewer and distiller, is modified chiefly by the proportion of
gluten which the barley contains. That which contains the least gluten,
and therefore the most starch, will melt the most easily and the most
completely, and will yield the strongest beer or spirit from the same
quantity of grain. Hence the preference given by the brewer to the
malt of particular districts, even where the sample appears otherwise
inferior. Thus the brewers on the sea-board of the county of Durham
will not purchase the barley of their own neighbourhood, while Norfolk
grain can be had at a moderate increase of price. But that which
refuses to melt well in the hands of the brewer, will cause pigs and
other stock to thrive well in the hands of the feeder, and this is the
chief outlet for the barley which the brewer and distiller reject.
So far as a practical deduction can be drawn from the effects of
different manures on the proportion of gluten in barley, it would
appear that the larger the quantity of cow dung contained in the manure
applied to barley land—in other words, _the greater the numbers of
stock folded about the farm-yard, the more likely is the barley to be
such as will bring a high price from the brewer_.
The folding of _sheep_ produces a larger return (p. 206), from the
barley crop—while the folding of _cattle_ gives grain of a better
malting quality.
SECTION III.—INFLUENCE OF THE TIME OF CUTTING, ON THE QUANTITY AND
QUALITY OF THE PRODUCE.
The period at which hay is cut, or corn reaped, materially affects the
quantity (by weight) and the quality of the produce. It is commonly
known that when radishes are left too long in the ground they become
hard and woody—that the soft turnippy stem of the young cabbage
undergoes a similar change as the plant grows old,—and that the
artichoke becomes tough and uneatable if left too long uncut. The same
natural change goes on in the grasses which are cut for hay.
In the blades and stems of the young grasses there is much sugar,
which, as they grow up, is gradually changed, first into starch, and
then into woody fibre (pages 44 and 45.) The more completely the latter
change is effected—that is, the riper the plant becomes—the less sugar
and starch, both readily soluble substances, they contain. And though
it has been ascertained that woody fibre is not wholly indigestible,
but that the cow, for example, can appropriate a portion of it for food
as it passes through her stomach; yet the reader will readily imagine,
that those parts of the food which dissolve most easily, are also
likely—other things being equal—to be most nourishing to the animal.
It is ascertained, also, that the weight of hay or straw reaped, is
actually less when allowed to become fully ripe; and therefore, by
cutting soon after the plant has attained its greatest height, a larger
quantity, as well as a better quality of hay, will be obtained, while
the land also will be less exhausted.
The same remarks apply to crops of corn,—both to the straw and to the
grain they yield. The _rawer_ the crop is cut, the heavier and more
nourishing the straw. Within three weeks of being fully ripe, the straw
begins to diminish in weight, and the longer it remains uncut after
that time, the lighter it becomes and the less nourishing.
On the other hand, the ear which is sweet and milky a month before it
is ripe, gradually consolidates, the sugar changing into starch, and
the milk thickening into the gluten and the _albumen_[22] of the flour.
As soon as this change is nearly completed, or about a fortnight before
ripening, the grain contains the largest proportion of starch and
gluten; if reaped at this time, the bushel will be heavier, and will
yield the largest quantity of fine flour and the least bran.
[22] _Albumen_ is the name given by chemists to the _white of the egg_.
A small quantity of this substance is present in every kind of grain.
It is closely related to gluten.
At this period the grain has a thin skin, and hence the small quantity
of bran. But if the crop be still left uncut, the next natural step in
the ripening process is, to cover the grain with a better protection,
a thicker skin. A portion of the starch of the grain is changed into
woody fibre,—precisely as in the ripening of hay, of the soft shoots of
the dog-rose, and of the roots of the common radish. By this change,
therefore, the quantity of starch is lessened and the weight of husk
increased; hence the diminished yield of flour, and the increased
produce of bran.
Theory and experience, therefore, indicate about a fortnight before
full ripening as the most proper time for cutting corn. The skin is
then thinner, the grain fuller, the bushel heavier, the yield of flour
greater, the quantity of bran less; while, at the same time, the straw
is heavier, and contains more soluble matter than when it is left uncut
until it is considered to be fully ripe.[23]
[23] On this subject the reader will consult with advantage an
excellent practical paper in the _Quarterly Journal of Agriculture_ for
June 1841, by Mr. Hannam of North Deighton, Yorkshire, to whom I have
to express my obligations for information regarding the results of some
further experiments made by him during the last autumn (1841).
SECTION IV.—ON THE ABSOLUTE QUANTITY OF FOOD YIELDED BY DIFFERENT CROPS.
The quantity of food capable of yielding nourishment to man, which can
be grown from an acre of land of average quality, depends very much
upon the kind of crop we raise.
In seeds, when fully ripe, little sugar or gum is generally present,
and it is chiefly by the amount of starch and gluten they contain, that
their nutritive power is to be estimated. In bulbs, such as the turnip
and potato, sugar and gum are almost always present in considerable
quantity in the state in which these roots are consumed, and this is
especially the case with the turnip. These substances, therefore, must
be included among the nutritive ingredients of such kinds of food.
If we suppose an acre of land to yield the following quantities of the
usually cultivated crops, namely—
Of wheat, 25 bushels, or 1500 lbs.
Of barley, 38 ” or 2000 ”
Of oats, 50 ” or 2250 ”
Of peas, 15 ” or 1000 ”
Of beans, 25 ” or 1600 ”
Of Indian corn, 60 ” or 3120 ”
Of potatoes, 10 tons, or 22400 ”
Of turnips, 25 ” or 56000 ”
The weight of dry starch, gluten, sugar, and gum, reaped in each crop,
will be represented very nearly by the following numbers:—
Starch. Gluten and Sugar and Woody
Albumen. Gum. Fibre.
Wheat, 825 lbs. 315 lbs. 60 —
Barley, 1200 ” 120 ” 160 —
Oats, 1215 ” 100 ” 250 —
Peas, 420 ” 260 ” 20 —
Beans, 670 ” 370 ” — —
Indian corn, 2100 ” 280 ” 90 —
Potatoes, 2688 ” 224 ” — 1253
Turnips, 3090 ” 1400 ” 5000 —
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._
A man of sedentary habits, or whose occupation requires little bodily
exertion, may respire about 5 ounces of carbon in twenty-four hours—one
who takes moderate exercise, about 8 ounces—and one who has to undergo
violent bodily exertion, from 12 to 15 ounces.
If we take the mean quantity of 8 ounces, then to supply this alone, a
man must eat 18 ounces of starch or sugar every day. If he take it in
the form of wheaten bread, he will require 1¾ lbs. of bread, if in the
form of potatoes, about 7½ lbs. of raw potatoes, to supply the waste
caused by his respiratory organs alone.
When the habits are sedentary, 5 lbs. of potatoes may be sufficient,
when violent and continued exercise is taken, 12 to 15 lbs. may be too
little. At the same time, it must be observed, that where the supply is
less, the quantity of carbonic acid given off will either be less also,
or the deficiency will be supplied at the expense of the body itself.
In either case the strength will be impaired, and fresh food will be
required to recruit the exhausted frame.
2. _The food must repair the daily waste of the muscular parts of the
body._
When the body is full grown, a portion from every part of it is
daily abstracted by natural processes, and rejected either in the
perspiration or in the solid and fluid excrements. This portion must
be supplied by the food, or the strength will diminish—the frame will
gradually waste away.
The muscles of animals, of which lean beef and mutton are examples,
are generally coloured by blood, but when well washed with water, they
become quite white, and, with the exception of a little fat, are found
to consist of a white fibrous substance, to which the name of _fibrin_
has been given by chemists. The clot of the blood consists of the
same substance; while skin, hair, horn, and the organic part of the
bones, are composed of varieties of _gelatine_. This latter substance
is familiarly known in the form of _glue_, and though it differs in
its sensible properties, it is remarkably analogous to _fibrin_ in its
elementary constitution, as both of these substances are to the white
of the egg (_albumen_), to the curd of milk (_casein_), and to the
_gluten_ of flour. They all contain nitrogen, and all consist of the
four elementary bodies (organic elements), very nearly in the following
proportions:—
Carbon, 55
Hydrogen, 7
Nitrogen, 18
Oxygen, 20
----
100
They all contain, likewise, a small proportion of sulphur and of
phosphorus.
The quantity of one or other of these removed from the body in 24
hours, either in the perspiration or in the excretions, amounts to
_about five ounces_, containing 350 grains of nitrogen, and this waste
at least must be made up by the gluten or fibrin of the food.
In the 1¾ lb. of wheaten bread we have supposed to be eaten to supply
carbon for respiration, there will be contained also about 3 ounces
of gluten. Let the other 2 ounces be made up in beef, of which half a
pound contains 2 ounces of dry fibrin, and we have
For respiration. For waste of
muscle, &c.
1¾ lbs. of bread yielding 18 oz. starch and 3 oz. of gluten.
8 oz. of beef yielding 2 oz. of fibrin.
Total consumed by respiration,} } gluten or
and the ordinary waste, } 18 oz. starch and 5 oz.} fibrin.
If, again, the 7½ lbs. of potatoes be eaten, then in these are
contained about 2½ ounces of gluten or albumen, so that there remain 2½
ounces to be supplied by beef, eggs, milk, or cheese.
The reader, therefore, will understand why a diet which will keep up
the human strength is easiest compounded of a mixture of vegetable and
animal food. It is not merely that such a mixture is more agreeable
to the palate, or even that it is absolutely necessary,—for, as
already observed, the strength may be fully maintained by vegetable
food alone;—it is, that without animal food in one form or another,
so large a bulk of vegetable food must be consumed in order to supply
the requisite quantity of nitrogen in the form of gluten. Of ordinary
wheaten bread alone, about 3 lbs. daily must be eaten to supply the
nitrogen,[24] and there would then be a considerable waste of carbon
in the form of starch, by which the stomach would be overloaded, and
which, not being worked up by respiration, would pass off in the
excretions. The wants of the body would be equally supplied, and with
more ease, by 1¾ lbs. of bread and 4 ounces of cheese.
[24] The flour being supposed to contain 15 per cent. of dry gluten, on
which supposition all the above calculations are made.
Of rice, again, no less than 4 lbs. daily would be required to impart
to the system the required proportion of gluten; and it is a familiar
observation of those who have been in India and other countries, where
rice is the usual food of the people, that the degree to which the
natives distend, and apparently overload their stomachs with this
grain, is quite extraordinary.
The stomachs and other digestive apparatus of our domestic animals are
of larger dimensions, and they are able, therefore, to contain with
ease as much vegetable food, of almost any wholesome variety, as will
supply them with the quantity of nitrogen they may require. Yet every
feeder of stock knows that the addition of a small portion of oil-cake,
a substance rich in nitrogen, will not only fatten an animal more
speedily, but will also save a large _bulk_ of other kinds of food.
3. But the blood and other fluids of the body contain much _saline_
matter of various kinds, sulphates, muriates, phosphates, and other
saline compounds of potash, soda, lime, and magnesia. All these have
their special functions to perform in the animal economy, and of each
of them an undetermined quantity daily escapes from the body in the
perspiration, in the urine, or in the solid excretions. This quantity,
therefore, must be daily restored by the food.
No precise experiments have yet been made with the view of determining
how much saline matter is daily excreted from the body of a healthy
man, or in what proportions the different inorganic substances are
present in it; but it is satisfactorily ascertained, that without
a certain _sufficient_ supply, the animal will languish and decay,
even though carbon and nitrogen in the form of starch and gluten be
abundantly given to it. It is a wise and beautiful provision of nature,
therefore, that plants are so organized as to refuse to grow in a soil
from which they cannot readily obtain a supply of soluble inorganic
food, since that saline matter which ministers first to their own wants
is afterwards surrendered by them to the animals they are destined to
feed.
Thus the dead earth and the living animal are but parts of the same
system,—links in the same endless chain of natural existences,—the
plant is the connecting bond by which they are tied together on the one
hand,—the decaying animal matter which returns to the soil, connects
them on the other.
4. The solid bones of the animal are supplied from the same original
source,—the vegetable food on which they live. The bones of the cow
contain 55 per cent. of phosphate of lime, of the sheep 70, of the
horse 67, of the calf 54, and of the pig 52 lbs., in every hundred of
dry bone. All this must come from the vegetable food. Of the bone-earth
also, a portion,—perhaps a variable portion,—is every day rejected from
the animal; the food, therefore, must contain a daily supply, or that
which passes off will be taken from the substance of the bones, and the
animal will become feeble.
It is kindly provided by nature, that a certain proportion of this
ingredient of bones is always associated with the gluten of plants
in its various forms,—with the fibrin of animal muscle and with the
curd of milk. Hence, man, in using any of these latter along with his
vegetable food, obtains from them, with comparative ease, the quantity
of the earth of bones which is necessary to keep his system in repair;
while those animals which live upon vegetables alone, extract all they
require along with the gluten of the plants on which they feed.
The provision is very beautiful by which the young animal,—the muscle
and bones of which are rapidly growing,—is supplied with a larger
portion of nitrogenous food and of bone-earth, than are necessary to
maintain the healthy condition of the full grown animal. The milk of
the mother is the natural food from which its supplies are drawn.
The sugar of the milk supplies the comparatively small quantity of
carbon necessary for the respiration of the young animal; as it gets
older, the calf or young lamb crops green food for itself to supply
an additional portion. The curd of the milk (_casein_) yields the
materials of the growing muscles, and of the animal part of the
bones,—while dissolved along with the curd in the liquid milk is the
phosphate of lime, of which the earthy part of the bones is to be built
up. A glance at the constitution of milk will shew us how copious the
supply of all these substances is,—how beautifully the constitution
of the mother’s milk is adapted to the wants of her infant offspring.
Cow’s milk consists in 1000 parts by weight of—
Butter, 27 to 35
Cheesy matter (casein), 45 to 90
Milk sugar, 36 to 50
_Chloride of potassium_, and
a little chloride of sodium, 1½}
_Phosphates_, chiefly of _lime_, 2¼} to 10
Other salts, 6
Water, 882¼ to 815
----- ----
1000 1000
The quality of the milk, and, consequently, the proportions of the
several constituents above mentioned, vary with the breed of the
cow,—with the food on which it is supported,—with the time that has
elapsed since the period of calving,—with its age, its state of health,
and with the warmth of the weather;[25] but in all cases this fluid
contains the same substances, though in different quantities.
[25] In warm weather the milk contains more butter, in cold weather
more cheese and sugar.
Milk of the quality above analyzed contains, in every ten gallons,
4½ lbs. of casein, equal to the formation of 18 lbs. of ordinary
muscle, and 3½ ounces of phosphate of lime (bone-earth), equal to
the production of 7 ounces of dry bone. But from the casein have to
be formed the skin, the hair, the horn, the hoof, &c. as well as the
muscle, and in all these is contained also a minute portion of the
bone-earth. A portion of all the ingredients of the milk likewise
passes off in the ordinary excretions, and yet every one knows how
rapidly young animals thrive, when allowed to consume the whole of the
milk which nature has provided as their most suitable nourishment.
And whence does the mother derive all this gluten and bone-earth, by
which she can not only repair the natural waste of her own full grown
body, but from which she can spare enough also to yield so large a
supply of nourishing milk? She must extract them from the vegetables on
which she lives, and they again from the soil.
The quantity of solid matter thus yielded by the cow in her milk is
really very large, if we look at the produce of an entire year. If the
average yield of milk be 3000 quarts, or 750 gallons in a year—every 10
gallons of which contain bone-earth enough to form about 7 ounces of
dry bone—then the milking of the cow alone exhausts her of the earthy
ingredients of 33 lbs. of dry bone. And this she draws necessarily from
the soil!
If this milk be consumed on the spot, then all returns again to the
soil in the annual manuring of the land. Let it be carried for sale
to a distance, or let it be converted into cheese and butter, and in
this form exported, there will then be a yearly drain upon the land
of the materials of bones, from this cause alone, equal to 30 lbs. of
bone-dust. After the lapse of centuries, it is conceivable that old
pasture lands in cheese and dairy countries should become poor in the
materials of bones—and that in such districts, as now in Cheshire, the
application of bone-dust should entirely alter the character of the
grasses, and renovate the old pastures.
Thus, as was stated at the commencement of the present section the
study of the nature, and functions of the food of animals throws
additional light upon the nature also and final uses of the food of
plants. It even teaches us what to look for in the soil—what a fertile
soil _must_ contain that it may grow nourishing food—what we must add
to the soil when chemical analysis fails to detect its actual presence,
or when the food it produces is unable to supply all that the animal
requires.
The principles above explained, therefore, shew that the value of any
vegetable production, considered as the _sole_ food of an animal, is
not to be judged of—cannot, in short, be accurately determined—by
the amount it may contain of any _one_ of those substances, _all_ of
which together are necessary to build up the growing body of the young
animal, and to repair the natural waste of such as have attained to
their fullest size.
Hence the failure of the attempts that have been made to support the
lives of animals by feeding them upon pure starch or sugar alone. These
substances would supply carbon for respiration, but all the natural
waste of nitrogen, of saline matter, and of earthy phosphates, must
have been drawn from the existing solids and fluids of their living
bodies. The animals in consequence pined away, and sooner or later died.
Some have expressed surprise that animals have refused to thrive,
and have ultimately died, when fed upon animal jelly or gelatine
(from bones) alone, nourishing though that substance _as part of the
food_ undoubtedly is. When given in sufficient quantity, gelatine
might indeed supply carbon enough for respiration, with a great waste
of nitrogen, but it is deficient in the saline ingredients which a
naturally nourishing food contains.
Even on the natural mixture of starch and gluten in fine white bread,
dogs have been unable to live beyond 50 days, though others fed on
household bread, containing a portion of the bran—in which earthy
matter more largely resides—continued to thrive long after. It is
immaterial whether the general quantity of the _whole_ food be reduced
too low, or whether _one_ of its necessary ingredients only be too much
diminished or entirely withdrawn. In either case, the effect will be
the same—the animal will pine away, and sooner or later die.
SECTION VII.—OF THE PRACTICAL AND THEORETICAL VALUE OF DIFFERENT KINDS
OF FOOD.
From what has been stated in the preceding section, it appears,
that, for various reasons, different kinds of food are not equally
nourishing. This fact is of great importance, not only in the
preparation of human food, but also in the feeding of stock. It has,
therefore, been made the subject of experiment by many practical
agriculturists, with the following general results.
If common hay be taken as the standard of comparison, then to yield
the same amount of nourishment with 10 lbs. of hay, a weight of the
other kinds of food must be given, which is represented by the number
opposite to each in the following table:—
Hay, 10 Carrots, 25 to 30
Clover hay, 8 to 10 Turnips, 50
Green clover, 45 to 50 Cabbage, 20 to 30
Wheat straw, 40 to 50 Pease and Beans, 3 to 5
Barley straw, 20 to 40 Wheat, 5 to 6
Oat straw, 20 to 40 Barley, 5 to 6
Pea straw, 10 to 15 Oats, 4 to 7
Potatoes, 20 Indian corn, 5
Old potatoes, 40? Oil-cake, 2 to 4
It is found in practice, as the above table shews, that twenty stones
of potatoes or three of oil-cake will nourish an animal as much as ten
stones of hay, and five stones of oats as much as either. Something,
however, will depend upon the quality of each kind of food, and upon
the age and constitution of the animal. The skilful feeder of stock
knows also the value of a change of food, or of a mixture of the
different kinds of vegetable food he may have at his command.
The nutritive value of different kinds of food has also been
represented theoretically, by supposing it to be very nearly in
proportion to the quantity of nitrogen, or of gluten, which vegetables
contain. Though this cannot be considered as a correct principle,
yet as the ordinary kind of food on which stock is fed contains in
general an ample supply of carbon for respiration, with a comparatively
small proportion of nitrogen, these theoretical determinations are by
no means without their value, and they approach in many cases very
closely to the practical values above given, as deduced from actual
trial. Thus, assuming that 10 lbs. of hay yield a certain amount
of nourishment, then of the other vegetable substances it will be
necessary, according to theory, to give the following quantities, in
order to produce the same effect:
Hay, 10 Turnips, 60
Clover hay, 8 Carrots, 35
Vetch hay,[26] 4 Cabbage, 30 to 40
Wheat straw, 52 Pease and Beans, 2 to 3
Barley straw, 52 Wheat, 5
Oat straw, 55 Barley, 6
Pea straw, 6 Oats, 5
Potatoes, 28 Indian corn, 6
Old potatoes, 40 Oil-cake, 2
[26] Both cut in flower.
If the feeder be careful to supply his stock with a mixture or
occasional change of food, he may very safely regulate the quantity of
any one he ought to substitute for a given weight of any of the others,
by the numbers in the above tables—since the theoretical and practical
results do not in general very greatly differ.
As has been already stated, it is not strictly correct that this or
that kind of vegetable is more fitted to sustain animal life, simply
because of the larger proportion of nitrogen it contains; but it
is wisely provided, that along with this nitrogen in all plants,
a certain proportion of starch or sugar and of saline and earthy
matter are always associated—so that the quantity of nitrogen may be
considered as a rough practical index of the proportion of some of the
important saline and earthy ingredients also.
An important practical lesson on this subject is taught us by the study
of the wise provisions of Nature. Not only does the milk of the mother
contain all the elements of a nutritive food mixed up together—as the
egg does also for the unhatched bird—but in rich natural pastures the
same mixture uniformly occurs. Hence, in cropping the mixed herbage,
the animal introduces into its stomach portions of various plants—some
abounding more in starch or sugar, some more in gluten or albumen, some
naturally richer in saline, others in earthy constituents; and out of
these varied materials the digestive organs select a due proportion of
each, and reject the rest. Wherever a pasture becomes usurped by one or
two grasses—either animals cease to thrive upon it, or they must crop a
much larger quantity of food to supply the natural waste of _all_ the
parts of their bodies.
It may indeed be assumed as almost a general principle, that whenever
animals are fed on one kind of vegetable only, there is a waste of one
or other of the necessary elements of animal food, and that the great
lesson on this subject taught us by nature is, that, by a judicious
admixture, not only is food economised, but the labour imposed upon the
digestive organs is also materially diminished.
SECTION VIII.—CONCLUDING OBSERVATIONS.
In this little work, now brought to a close, I have presented the
reader with a slight, and I hope plain and familiar, sketch of the
various topics connected with practical agriculture, on which the
sciences of chemistry and geology are fitted to throw the greatest
light.
We have studied the general characters of the organic and inorganic
elements of which the parts of plants are made up, and the several
compounds of these elements which are of the greatest importance in
the vegetable kingdom. We have examined the nature of the seed,—seen
by what beautiful provision it is fed during its early germination—in
what form the elements by which it is nourished are introduced into
the circulation of the young plant when the functions of the seed are
discharged,—and how earth, air, and water are all made to minister
to its after-growth. We have considered the various chemical changes
which take place within the growing plant, during the formation of its
woody stem, the blossoming of its flower, and the ripening of its seed
or fruit,—and have traced the further changes it undergoes, when, the
functions of its short life being discharged, it hastens to serve other
purposes, by mingling with the soil, and supplying food to new races.
The soils themselves in which plants grow, their nature, their origin,
the causes of their diversity in mineral character, and in natural
productiveness, have each occupied a share of our attention—while
the various means of improving their agricultural value by manuring
or otherwise, have been practically considered, and theoretically
explained. Lastly, we have glanced at the comparative worth of the
various products of the land, as food for man or other animals, and
have briefly illustrated the principles upon which the feeding of
animals and the relative nutritive powers of the vegetables on which
they live are known to depend.
In this short and familiar treatise I have not sought so much to
_satisfy_ the demands of the philosophical agriculturist, as to
_awaken_ the curiosity of my less instructed reader, to shew him how
much interesting as well as practically useful information chemistry
and geology are able and willing to impart to him, and thus to allure
him in quest of further knowledge and more accurate details to my
larger work,[27] of which the present exhibits only a brief outline.
[27] LECTURES _on Agricultural Chemistry and Geology_.
J. P. Wright, Printer, 18 New street, N. Y.
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