Practical men have long been of opinion that the digestion of food,
either animal or vegetable,—the passing of it through the bodies of
animals,—enriches its fertilizing power, weight for weight, when
added to the land. Hence, in causing animals to eat up as much of the
vegetable productions of the farm as possible, it is supposed that not
only is so much food saved, but that the value of the remainder in
fertilizing the land is greatly increased. In a subsequent section we
shall see how far theory serves to throw light upon these opinions.
(See Section IV., p. 182 to 186.)
I. LIQUID EXCRETIONS.
The digested animal substances usually employed as manures are, the
urine of the cow and the sheep, the solid excrements of the horse, the
cow, the sheep, and the pig, the droppings of pigeons and other birds,
and night-soil. The liquid manures act chiefly through the saline
substances they hold in solution, while the solid manures contain also
insoluble matters, which decay slowly in the soil, and there become
useful only after a time. The former, therefore, will influence
vegetation more powerfully at first; the action of the latter will be
less evident, but will continue to operate for a much longer period.
_Urine._—Human urine consists, in 1000 parts, of
Water, 932
_Urea_, and other organic matters containing nitrogen, 49
_Phosphates_ of ammonia, lime, soda, and magnesia, 6
_Sulphates_ of soda and ammonia, 7
Sal ammoniac and common salt, 6
----
1000
A thousand pounds of urine therefore contain 68 lbs. of dry fertilizing
matter of the richest quality, worth, _at the present rate of selling
artificial manures in this country_, at least 20s. a cwt. As each
person voids almost 1000 lb. of urine in a year, the national waste
incurred in this form amounts, at the above valuation, to 12s. a head.
And if five tons of farm-yard manure per acre, added year by year, will
keep a farm in good heart, four cwt. of the solid matter of urine would
probably have an equal effect; or the urine alone discharged into the
rivers by a population of 10,000 inhabitants would supply manure to a
farm of 1500 acres, yielding a return of 4500 quarters of corn or an
equivalent produce of other crops.
The urine of the cow is said to contain less water than that of man,
though of course much must depend upon the kind of food with which it
is fed. Reckoning, then, the large quantity of liquid manure that
is yielded by the cow (2000 or 3000 gallons a year), we may safely
estimate the solid matter given off by a healthy animal in this form in
twelve months at 1200 to 1500 pounds weight, worth, _if it were in the
dry state_, from £10 to £12 sterling. In the _liquid_ state, the urine
of one cow collected and preserved as it is in Flanders, is valued in
that country at about £2 a year. Any practical farmer may calculate for
himself, therefore, how much real wealth, taking it even at the Flemish
value, is lost in his own farm-yard—how much of the natural means of
reproductive industry passes into his drains or evaporates into the air.
This liquid manure is invaluable, when collected in tanks, for watering
the manure and compost heaps, and thus hastening their decomposition;
but great part of it may also be sprinkled directly upon the fields of
grass and upon the young corn, with the best effects. It must, however,
be permitted to stand till fermentation commences, and afterwards
diluted with a considerable quantity of water, before it will be in the
best condition for laying on the land.
_Urate._—In order to obtain the virtues of animal urine in a
concentrated form, the custom has been adopted of mixing burnt gypsum
with it, in the proportion of 10 lbs. to every 7 gallons, allowing the
mixture, occasionally stirred, to stand some time, pouring off the
liquid, and drying and crushing the gypsum. This is sold by manure
manufacturers under the name of _urate_. It never can possess, however,
the virtues of the urine, since it does not contain the soluble saline
substances, which the gypsum does not carry down with it. Except the
gypsum, indeed, 100 lbs. of urate contain no greater weight of saline
and organic matter than 10 gallons of urine. If it be true, then, as
the manufacturers state, that 3 or 4 cwt. of urate are sufficient
manure for an acre, the practical farmer will, I hope, draw the
conclusion,—not that it is well worth his while to venture his money
in trying a portion of it upon a piece of his land,—but that a far
more promising adventure will be to go to some expense in saving his
own liquid manure, and, after mixing it with burned gypsum, to lay it
abundantly upon all his fields.
II. SOLID EXCRETIONS.
_Cow and Horse Dung._—So much of the saline, nutritive, and soluble
organic matters from the cow pass off in the liquid form, that cow
dung is correctly called cold, since it does not readily heat and run
into fermentation. Mixed with other manures, however, or well diffused
through the soil, it aids materially in promoting vegetation. The horse
being fed generally on less liquid food, and discharging less urine,
yields a hotter and richer dung, which, however, answers best also when
mixed with other varieties. The dung of the swine is soft and _cold_,
like that of the cow, containing, like it, at least 75 per cent. of
water. As this animal lives on more varied food than any other reared
for the use of man, the manure obtained from it is also very variable
in quality. Applied alone, as a manure to roots, it is said to give
them an unpleasant taste, and even to injure the flavour of tobacco. It
answers best for hemp, and, it is said, also for hops; but, mixed with
other manures, it may be applied to any crop.
_Night-soil_ is probably the most valuable, and yet, in Europe at
least, the most disliked and neglected of all the solid animal manures.
It varies no doubt in richness with the food of the inhabitants of each
district,—chiefly with the quantity of animal food they consume,—but
when dry, no other solid manure, weight for weight, can probably be
compared with it in general efficacy. It contains much soluble and
saline matter, and as it is made up from the constituents of the food
we eat, of course it contains most of those elementary substances
which are necessary to the growth of the plants on which we principally
live.
Attempts have been made to dry this manure also, so as to render it
more portable,—to destroy its unpleasant smell, so as to reconcile
practical men to a more general use of it,—and by certain chemical
additions, to prevent the waste of ammonia and other volatile
substances, which are apt to escape and be lost when this and other
powerful animal manures begin to putrify through decay. In Paris,
Berlin, and other large cities, the night-soil, dried first in the air
with or without a mixture of gypsum or lime, then upon drying plates,
and finally in stoves, is sold under the name of _poudrette_, and is
extensively exported in casks to various parts of the country. In
London also it is dried with various mixtures, while in others of our
large towns an _animalized charcoal_ is prepared by mixing and drying
night-soil with gypsum and ordinary wood charcoal in fine powder.
The half-burned peat above described (p. 80,) would answer well for
such a purpose, while few simple and easily attainable substances would
make a better compost with night-soil, and more thoroughly preserve its
virtues, than half-dry peat or rich vegetable soil, mixed with more or
less marl or gypsum. It is impossible to estimate the proportion of
waste which this valuable manure undergoes by being allowed to ferment,
without mixture, in the open air.
_Taffo._—In China it is kneaded into cakes with clay, which are dried
in the air, and, under the name of taffo, form an important article of
export from all the large cities of the empire.
_Pigeons’ Dung._—The dung of all birds is found to possess eminent
fertilizing virtues. Some varieties are stronger than others, or more
immediate in their action, and all are improved for the use of the
farmer by being some time kept, either alone or in compost. In Flanders
the manure of one hundred pigeons is considered worth 20s. a year for
agricultural purposes.
_Guano_ is the name given by the natives of Peru to the dung of
sea-fowl, which in former periods used to be deposited in vast
quantities on the rocky shores and isles of the Peruvian coast. The
numerous shipping of modern times has disturbed and driven away many of
the sea-fowl, so that comparatively little of their recent droppings
is now preserved or collected. Ancient heaps of it, however, still
exist in many places, more or less covered up with drifted sand, and
also more or less decomposed. These are now largely excavated for
exportation, not only to different parts of the coast of Peru, as seems
to have been the case from the most remote periods, but also to Europe,
and especially to England. It is at present sold at 20s. a cwt. in this
country, and is capable of entirely replacing farm-yard dung,—that is
to say, turnips may be manured successfully with guano alone;—but it
has not yet been satisfactorily determined that the English farmer can
afford to use it in this way to any extent, at the price now asked for
it.
The dung of birds possesses the united virtues of both the liquid and
solid excretions of other animals. It contains every part of the food
of the bird, with the exception of what is absolutely necessary for
the support and for the right discharge of the functions of its own
body. It is thus fitted, therefore, to return to the plant a greater
number of those substances on which plants live, than either the solid
or the fluid excrements of other animals; in other words, to be more
nourishing to vegetable growth.