restoration of the elementary constituents of the soil which have
been gradually drawn from it in the shape of grain and cattle. If
the land I am speaking of had not been manured during those 16
years, not more than one-half, or perhaps than one-third part of the
carbon and nitrogen would have been produced. We owe it to the
animal excrements, that it equalled in production the meadow-land,
and this, because they restored the mineral ingredients of the soil
removed by the crops. All that the supply of manure accomplished,
was to prevent the land from becoming poorer in these, than the
meadow which produces 2,500 pounds of hay. We withdraw from the
meadow in this hay as large an amount of mineral substances as we do
in one harvest of grain, and we know that the fertility of the
meadow is just as dependent upon the restoration of these
ingredients to its soil, as the cultivated land is upon manures. Two
meadows of equal surface, containing unequal quantities of inorganic
elements of nourishment,--other conditions being equal,--are very
unequally fertile; that which possesses most, furnishes most hay. If
we do not restore to a meadow the withdrawn elements, its fertility
decreases. But its fertility remains unimpaired, with a due supply
of animal excrements, fluid and solid, and it not only remains the
same, but may be increased by a supply of mineral substances alone,
such as remain after the combustion of ligneous plants and other
vegetables; namely, ashes. Ashes represent the whole nourishment
which vegetables receive from the soil. By furnishing them in
sufficient quantities to our meadows, we give to the plants growing
on them the power of condensing and absorbing carbon and nitrogen by
their surface. May not the effect of the solid and fluid excrements,
which are the ashes of plants and grains, which have undergone
combustion in the bodies of animals and of man, be dependent upon
the same cause? Should not the fertility, resulting from their
application, be altogether independent of the ammonia they contain?
Would not their effect be precisely the same in promoting the
fertility of cultivated plants, if we had evaporated the urine, and
dried and burned the solid excrements? Surely the cerealia and
leguminous plants which we cultivate must derive their carbon and
nitrogen from the same source whence the graminea and leguminous
plants of the meadows obtain them! No doubt can be entertained of
their capability to do so.
In Virginia, upon the lowest calculation, 22 pounds weight of
nitrogen were taken on the average, yearly, from every morgen of the
wheat-fields. This would amount, in 100 years, to 2,200 pounds
weight. If this were derived from the soil, every morgen of it must
have contained the equivalent of 110,000 pounds weight of animal
excrements (assuming the latter, when dried, at the temperature of
boiling water, to contain 2 per cent.).
In Hungary, as I remarked in a former Letter, tobacco and wheat have
been grown upon the same field for centuries, without any supply of
nitrogenised manure. Is it possible that the nitrogen essential to,
and entering into, the composition of these crops, could have been
drawn from the soil?
Every year renews the foliage and fruits of our forests of beech,
oak, and chesnuts; the leaves, the acorns, the chesnuts, are rich in
nitrogen; so are cocoa-nuts, bread-fruit, and other tropical
productions. This nitrogen is not supplied by man, can it indeed be
derived from any other source than the atmosphere?
In whatever form the nitrogen supplied to plants may be contained in
the atmosphere, in whatever state it may be when absorbed, from the
atmosphere it must have been derived. Did not the fields of Virginia
receive their nitrogen from the same source as wild plants?
Is the supply of nitrogen in the excrements of animals quite a
matter of indifference, or do we receive back from our fields a
quantity of the elements of blood corresponding to this supply?
The researches of Boussingault have solved this problem in the most
satisfactory manner. If, in his grand experiments, the manure which
he gave to his fields was in the same state, i.e. dried at 110 deg
in a vacuum, as it was when analysed, these fields received, in 16
years, 1,300 pounds of nitrogen. But we know that by drying all the
nitrogen escapes which is contained in solid animal excrements, as
volatile carbonate of ammonia. In this calculation the nitrogen of
the urine, which by decomposition is converted into carbonate of
ammonia, has not been included. If we suppose it amounted to half as
much as that in the dried excrements, this would make the quantity
of nitrogen supplied to the fields 1,950 pounds.
In 16 years, however, as we have seen, only 1,517 pounds of
nitrogen, was contained in their produce of grain, straw, roots, et
cetera--that is, far less than was supplied in the manure; and in
the same period the same extent of surface of good meadow-land (one
hectare = a Hessian morgen), which received no nitrogen in manure,
2,062 pounds of nitrogen.
It is well known that in Egypt, from the deficiency of wood, the
excrement of animals is dried, and forms the principal fuel, and
that the nitrogen from the soot of this excrement was, for many
centuries, imported into Europe in the form of sal ammoniac, until a
method of manufacturing this substance was discovered at the end of
the last century by Gravenhorst of Brunswick. The fields in the
delta of the Nile are supplied with no other animal manures than the
ashes of the burnt excrements, and yet they have been proverbially
fertile from a period earlier than the first dawn of history, and
that fertility continues to the present day as admirable as it was
in the earliest times. These fields receive, every year, from the
inundation of the Nile, a new soil, in its mud deposited over their
surface, rich in those mineral elements which have been withdrawn by
the crops of the previous harvest. The mud of the Nile contains as
little nitrogen as the mud derived from the Alps of Switzerland,
which fertilises our fields after the inundations of the Rhine. If
this fertilising mud owed this property to nitrogenised matters;
what enormous beds of animal and vegetable exuviae and remains ought
to exist in the mountains of Africa, in heights extending beyond the
limits of perpetual snow, where no bird, no animal finds food, from
the absence of all vegetation!
Abundant evidence in support of the important truth we are
discussing, may be derived from other well known facts. Thus, the
trade of Holland in cheese may be adduced in proof and illustration
thereof. We know that cheese is derived from the plants which serve
as food for cows. The meadow-lands of Holland derive the nitrogen of
cheese from the same source as with us; i.e. the atmosphere. The
milch cows of Holland remain day and night on the grazing-grounds,
and therefore, in their fluid and solid excrements return directly
to the soil all the salts and earthy elements of their food: a very
insignificant quantity only is exported in the cheese. The fertility
of these meadows can, therefore, be as little impaired as our own
fields, to which we restore all the elements of the soil, as manure,
which have been withdrawn in the crops. The only difference is, in
Holland they remain on the field, whilst we collect them at home and
carry them, from time to time, to the fields.
The nitrogen of the fluid and solid excrements of cows, is derived
from the meadow-plants, which receive it from the atmosphere; the
nitrogen of the cheese also must be drawn from the same source. The
meadows of Holland have, in the lapse of centuries, produced
millions of hundredweights of cheese. Thousands of hundredweights
are annually exported, and yet the productiveness of the meadows is
in no way diminished, although they never receive more nitrogen than
they originally contained.
Nothing then can be more certain than the fact, that an exportation
of nitrogenised products does not exhaust the fertility of a
country; inasmuch as it is not the soil, but the atmosphere, which
furnishes its vegetation with nitrogen. It follows, consequently,
that we cannot increase the fertility of our fields by a supply of
nitrogenised manure, or by salts of ammonia, but rather that their
produce increases or diminishes, in a direct ratio, with the supply
of mineral elements capable of assimilation. The formation of the
constituent elements of blood, that is, of the nitrogenised
principles in our cultivated plants, depends upon the presence of
inorganic matters in the soil, without which no nitrogen can be
assimilated even when there is a most abundant supply. The ammonia
contained in animal excrements exercises a favourable effect,
inasmuch as it is accompanied by the other substances necessary to
accomplish its transition into the elements of the blood. If we
supply ammonia associated with all the conditions necessary to its
assimilation, it ministers to the nourishment of the plants; but if
this artificial supply is not given they can derive all the needed
nitrogen from the atmosphere--a source, every loss from which is
restored by the decomposition of the bodies of dead animals and the
decay of plants. Ammonia certainly favours, and accelerates, the
growth of plants in all soils, wherein all the conditions of its
assimilation are united; but it is altogether without effect, as
respects the production of the elements of blood where any of these
conditions are wanting. We can suppose that asparagin, the active
constituent of asparagus, the mucilaginous root of the marsh-mallow,
the nitrogenised and sulphurous ingredients of mustard-seed, and of
all cruciferous plants, may originate without the aid of the mineral
elements of the soil. But if the principles of those vegetables,
which serve as food, could be generated without the co-operation of
the mineral elements of blood, without potash, soda, phosphate of
soda, phosphate of lime, they would be useless to us and to
herbivorous animals as food; they would not fulfil the purpose for
which the wisdom of the Creator has destined them. In the absence of
alkalies and the phosphates, no blood, no milk, no muscular fibre
can be formed. Without phosphate of lime our horses, sheep and
cattle, would be without bones.
In the urine and in the solid excrements of animals we carry
ammonia, and, consequently, nitrogen, to our cultivated plants, and
this nitrogen is accompanied by all the mineral elements of food
exactly in the same proportions, in which both are contained in the
plants which served as food to the animals, or what is the same, in
those proportions in which both can serve as nourishment to a new
generation of plants, to which both are essential.
The effect of an artificial supply of ammonia, as a source of
nitrogen, is, therefore, precisely analogous to that of humus as a
source of carbonic acid--it is limited to a gain of time; that is,
it accelerates the development of plants. This is of great
importance, and should always be taken into account in gardening,
especially in the treatment of the kitchen-garden; and as much as
possible, in agriculture on a large scale, where the time occupied
in the growth of the plants cultivated is of importance.
When we have exactly ascertained the quantity of ashes left after
the combustion of cultivated plants which have grown upon all
varieties of soil, and have obtained correct analyses of these
ashes, we shall learn with certainty which of the constituent
elements of the plants are constant and which are changeable, and we
shall arrive at an exact knowledge of the sum of all the ingredients
we withdraw from the soil in the different crops.
With this knowledge the farmer will be able to keep an exact record,
of the produce of his fields in harvest, like the account-book of a
well regulated manufactory; and then by a simple calculation he can
determine precisely the substances he must supply to each field, and
the quantity of these, in order to restore their fertility. He will
be able to express, in pounds weight, how much of this or that
element he must give in order to augment its fertility for any given
kind of plants.
These researches and experiments are the great desideratum of the
present time. TO THE UNITED EFFORTS OF THE CHEMISTS OF ALL COUNTRIES
WE MAY CONFIDENTLY LOOK FOR A SOLUTION OF THESE GREAT QUESTIONS, and
by the aid of ENLIGHTENED AGRICULTURISTS we shall arrive at a
RATIONAL system of GARDENING, HORTICULTURE, and AGRICULTURE,
applicable to every country and all kinds of soil, and which will be
based upon the immutable foundation of OBSERVED FACTS and
PHILOSOPHICAL INDUCTION.
LETTER XVI
My dear Sir,
My recent researches into the constituent ingredients of our
cultivated fields have led me to the conclusion that, of all the
elements furnished to plants by the soil and ministering to their
nourishment, the phosphate of lime--or, rather, the phosphates
generally--must be regarded as the most important.
In order to furnish you with a clear idea of the importance of the
phosphates, it may be sufficient to remind you of the fact, that the
blood of man and animals, besides common salt, always contains
alkaline and earthy phosphates. If we burn blood and examine the
ashes which remain, we find certain parts of them soluble in water,
and others insoluble. The soluble parts are, common salt and
alkaline phosphates; the insoluble consist of phosphate of lime,
phosphate of magnesia, and oxide of iron.
These mineral ingredients of the blood--without the presence of
which in the food the formation of blood is impossible--both man and
animals derive either immediately, or mediately through other
animals, from vegetable substances used as food; they had been
constituents of vegetables, they had been parts of the soil upon
which the vegetable substances were developed.
If we compare the amount of the phosphates in different vegetable
substances with each other, we discover a great variety, whilst
there is scarcely any ashes of plants altogether devoid of them, and
those parts of plants which experience has taught us are the most
nutritious, contain the largest proportion. To these belong all
seeds and grain, especially the varieties of bread-corn, peas,
beans, and lentils.
It is a most curious fact that if we incinerate grain or its flour,
peas, beans, and lentils, we obtain ashes, which are distinguished
from the ashes of all other parts of vegetables by the absence of
alkaline carbonates. The ashes of these seeds when recently
prepared, do not effervesce with acids; their soluble ingredients
consist solely of alkaline phosphates, the insoluble parts of
phosphate of lime, phosphate of magnesia, and oxide of iron:
consequently, of the very same salts which are contained in blood,
and which are absolutely indispensable to its formation. We are thus
brought to the further indisputable conclusion that no seed suitable
to become food for man and animals can be formed in any plant
without the presence and co-operation of the phosphates. A field in
which phosphate of lime, or the alkaline phosphates, form no part of
the soil, is totally incapable of producing grain, peas, or beans.
An enormous quantity of these substances indispensable to the
nourishment of plants, is annually withdrawn from the soil and
carried into great towns, in the shape of flour, cattle, et cetera.
It is certain that this incessant removal of the phosphates must
tend to exhaust the land and diminish its capability of producing
grain. The fields of Great Britain are in a state of progressive
exhaustion from this cause, as is proved by the rapid extension of
the cultivation of turnips and mangel wurzel--plants which contain
the least amount of the phosphates, and therefore require the
smallest quantity for their development. These roots contain 80 to
92 per cent. of water. Their great bulk makes the amount of produce
fallacious, as respects their adaptation to the food of animals,
inasmuch as their contents of the ingredients of the blood, i.e. of
substances which can be transformed into flesh, stands in a direct
ratio to their amount of phosphates, without which neither blood nor
flesh can be formed.
Our fields will become more and more deficient in these essential
ingredients of food, in all localities where custom and habits do
not admit the collection of the fluid and solid excrements of man,
and their application to the purposes of agriculture. In a former
letter I showed you how great a waste of phosphates is unavoidable
in England, and referred to the well-known fact that the importation
of bones restored in a most admirable manner the fertility of the
fields exhausted from this cause. In the year 1827 the importation
of bones for manure amounted to 40,000 tons, and Huskisson estimated
their value to be from L 100,000 to L 200,000 sterling. The
importation is still greater at present, but it is far from being
sufficient to supply the waste.
Another proof of the efficacy of the phosphates in restoring
fertility to exhausted land is afforded by the use of the guano--a
manure which, although of recent introduction into England, has
found such general and extensive application.
We believe that the importation of one hundred-weight of guano is
equivalent to the importation of eight hundred-weight of wheat--the
hundred-weight of guano assumes in a time which can be accurately
estimated the form of a quantity of food corresponding to eight
hundred-weight of wheat. The same estimate is applicable in the
valuation of bones.
If it were possible to restore to the soil of England and Scotland
the phosphates which during the last fifty years have been carried
to the sea by the Thames and the Clyde, it would be equivalent to
manuring with millions of hundred-weights of bones, and the produce
of the land would increase one-third, or perhaps double itself, in
five to ten years.
We cannot doubt that the same result would follow if the price of
the guano admitted the application of a quantity to the surface of
the fields, containing as much of the phosphates as have been
withdrawn from them in the same period.
If a rich and cheap source of phosphate of lime and the alkaline
phosphates were open to England, there can be no question that the
importation of foreign corn might be altogether dispensed with after
a short time. For these materials England is at present dependent
upon foreign countries, and the high price of guano and of bones
prevents their general application, and in sufficient quantity.
Every year the trade in these substances must decrease, or their
price will rise as the demand for them increases.
According to these premises, it cannot be disputed, that the annual
expense of Great Britain for the importation of bones and guano is
equivalent to a duty on corn: with this difference only, that the
amount is paid to foreigners in money.
To restore the disturbed equilibrium of constitution of the
soil,--to fertilise her fields,--England requires an enormous supply
of animal excrements, and it must, therefore, excite considerable
interest to learn, that she possesses beneath her soil beds of
fossil guano, strata of animal excrements, in a state which will
probably allow of their being employed as a manure at a very small
expense. The coprolithes discovered by Dr. Buckland, (a discovery of
the highest interest to Geology,) are these excrements; and it seems
extremely probable that in these strata England possesses the means
of supplying the place of recent bones, and therefore the principal
conditions of improving agriculture--of restoring and exalting the
fertility of her fields.
In the autumn of 1842, Dr. Buckland pointed out to me a bed of
coprolithes in the neighbourhood of Clifton, from half to one foot
thick, inclosed in a limestone formation, extending as a brown
stripe in the rocks, for miles along the banks of the Severn. The
limestone marl of Lyme Regis consists, for the most part, of
one-fourth part of fossil excrements and bones. The same are
abundant in the lias of Bath, Eastern and Broadway Hill, near
Evesham. Dr. Buckland mentions beds, several miles in extent, the
substance of which consists, in many places, of a fourth part of
coprolithes.
Pieces of the limestone rock in Clifton, near Bristol, which is rich
in coprolithes and organic remains, fragments of bones, teeth, &c.,
were subjected to analysis, and were found to contain above 18 per
cent. of phosphate of lime. If this limestone is burned and brought
in that state to the fields, it must be a perfect substitute for
bones, the efficacy of which as a manure does not depend, as has
been generally, but erroneously supposed, upon the nitrogenised
matter which they contain, but on their phosphate of lime.
The osseous breccia found in many parts of England deserves especial
attention, as it is highly probable that in a short time it will
become an important article of commerce.
What a curious and interesting subject for contemplation! In the
remains of an extinct animal world, England is to find the means of
increasing her wealth in agricultural produce, as she has already
found the great support of her manufacturing industry in fossil
fuel,--the preserved matter of primeval forests,--the remains of a
vegetable world. May this expectation be realised! and may her
excellent population be thus redeemed from poverty and misery!
End of Project Gutenberg's Familiar Letters of Chemistry, by Justus Liebig