The fertilizing power of animal manures, in general, is dependent,
like that of the soil itself, upon the happy admixture they contain
of a great number, if not of all, those substances which are required
by plants in the universal vegetation of the globe. Nothing they
contain, therefore, is without its share of influence upon their
general effects, yet the amount of nitrogen present in each affords the
readiest and most simple criterion by which their agricultural value,
compared with that of vegetable matters and with that of each other,
can be pretty nearly estimated.
In reference to their relative quantities of nitrogen, therefore, they
have been arranged in the following order, the number opposite to each
representing the weight in pounds which is equivalent to or would
produce the same sensible effect upon the soil as 100 lbs. of farm-yard
manure.
Farm-yard manure, 100
Solid excrements of the cow, 125
” ” ” horse, 73
Liquid ” ” cow, 91
” ” ” horse, 16
Mixed ” ” cow, 98
” ” ” horse, 54
” ” ” sheep, 36
” ” ” pig, 64
Dry flesh, 3
Pigeons’ dung, 5
Flemish liquid manure, 200
Liquid blood, 15
Dry blood, 4
Feathers, 3
Cow hair, 3
Horn shavings, 3
Dry woollen rags, 2½
It is probable that the numbers in this table do not err very widely
from the true relative value of these different manures, in so far as
the _organic_ matter they severally contain is concerned. The reader
will bear in mind, however,
1. That the most powerful substances in this table, woollen rags, for
example,—2½ lbs. of which are equal in virtue to 100 lbs. of farm-yard
manure,—may yet shew less immediate sensible effect upon the crop than
an equal weight of sheep’s dung, or even of urine. Such dry substances
are long in dissolving and decomposing, and continue to evolve
fertilizing matter, after the softer and more fluid manures have spent
their force. Thus, while farm-yard manure or rape dust will immediately
hasten the growth of turnips, woollen rags will come into operation at
a later period, and prolong their growth into the autumn.
2. That besides their general relative value, as represented in the
above table, each of these substances has a further special value not
here exhibited, dependent upon the kind and quantity of saline and
other inorganic matter which they severally contain. Thus three of dry
flesh are equal to five of pigeons’ dung, in so far as the _organic_
part is concerned; but the latter contains also a considerable quantity
of bone-earth and of saline matter scarcely present at all in the
former. Hence pigeons’ dung will benefit vegetation in circumstances
where dry flesh would in some degree fail. So the liquid excretions
contain much important saline matter not present in the solid
excretions,—not present either in such substances as horn, wool, and
hair,—and, therefore, each must be capable of exercising an influence
upon vegetation peculiar to itself.
Hence the practical farmer sees the reason why no one _simple_ manure
can long answer on the same land; and why in all ages and countries the
habit of employing _mixed_ manures and artificial composts has been
universally diffused.