135 
THE CULTIVATOR. 
Agricultural Chemistry. 
BY HENRY R. MADDEN, ESQ. L. R. C. S. EDINBURGH. 
[From the Edinburgh Quarterly Journal of Agriculture.'] 
We have now to commence the most important, but at the 
same time by far the most difficult branch of our subject; 
namely, the Philosophy of Manure, or the scientific principles 
upon which the cultivation of plants is founded. To accom¬ 
plish this, with facility and perspicuity, it will be necessary 
to divide the subject into the following heads. 
I. To give a clear view of the objects to be attained by the 
application of manure. 
II. An account of the composition, and respective value, of 
some of the more important manures. 
III. An account of the circumstances which should guide 
us in the choice of manure, and its application to various 
crops. 
IV. The economy of manure, or the methods to be adopt¬ 
ed in order to produce manure as quickly as possible, and 
likewise to apply it to the greatest advantage. 
I. There is no point connected with agriculture, in refer¬ 
ence to which more incomprehensible statements have been 
laid before the public, than those which have from time to 
time, and more especially lately, been published upon the 
subject of manure; and it appears to me that these could 
never have been conceived, far less made public, had due at¬ 
tention been given to that branch of the subject, to wdiich 
the present section is devoted, namely, the objects to be at¬ 
tained by the application of manure: these we shall now con¬ 
sider. We have already shewn that by far the most essential 
point to be attended to in the cultivation of plants, is to pre¬ 
sent to them a constant supply of organic matter, in a state 
capable of being rendered soluble in water; and we have 
moreover seen that this is accomplished, by adding to the 
soil, at certain intervals, various refuse matters, which are 
technically denominated manure, by which means all kinds 
of dead organic matter, are re-converted into living organized 
bodies; and consequently the objects of manuring may be de¬ 
scribed to be, the conversion of refuse matters into useful 
food; or in other words the duty and object of the farmer, is 
to convert manure into crops. This fact, however, appears to 
have been most determinedly overlooked by many late writers 
upon the subject, and in consequence there has been more 
nonsense and absurdity published in reference to this point, 
than one could have possibly imagined. Thus, for example 
we are most seriously told by a late writer upon fluid ma¬ 
nure, that “ there are many plants which by distillation yield 
a strong spirit, which is so powerful a manure, that, from 
some experiments he has himself performed, he confidently 
looks forwards to the time when the manure for an acre of 
land shall be contained in a quart bottle.” This statement 
is really almost too absurd too refute, were it not that the opi¬ 
nion appears to be gaining ground in some parts of England. 
I trust therefore that my more enlightened readers will ex¬ 
cuse me for occupying some space in proving the impossibility 
of such a thing being accomplished. It must be evident to 
all, who will take the trouble to think of the subject, that the 
weight of the crop must always bear some proportion to the 
weight of the organic matter in the soil; for, of what do ve¬ 
getables consist?—Of water, organic matter and earthy parti- 
ticles. Now the first and last of these are supplied by the soil 
itself (considered as a mineral substance;) but the organized 
portions can be supplied to the plant only by organic matter, 
previously existing in the soil; for although plants do obtain 
some of their carbon from the air, still this is but an inconsi¬ 
derable portion, and moreover much of the carbonic acid which 
yields that portion, has been supplied by the previous decom¬ 
position of organic matter. We may therefore infer, that 
should the above-mentioned author succeed in manuring an 
acre of land with the contents of a quart bottle, he will in time 
discover that the same article will be almost sufficient to con¬ 
tain his crop. But the believers of the above doctrine may 
say that the author has proved it by direct experiment, and 
consequently he must be either willingly deceiving the public, 
or must have some grounds for his statement. Now I have 
no doubt that the author is perfectly satisfied in his own 
mind that he is writing the truth, and I shall endeavor to 
shew how he has been misled. His powerful spirit, was of 
course applied to soil, (probably very rich garden mould) and 
the result was that it had a most powerful effect upon the 
veo-etation of that soil, and in fact its influence was felt by 
“ many succeeding crops:” but this by no means proves that 
his spirit is really a manure at all; it may act only as a chemi¬ 
cal agent in producing the more rapid decomposition of the 
vegetable fibre of the soil,.and thus rendering it soluble; and 
consequently his crops were produced by the original or garde 
matter of the soil, and not by his powerful spirit. For had he 
continued its application from time to time, and taken care 
to prevent any subsequent addition of fresh organic matter, 
he would have undoubtedly found that his soil became ex¬ 
hausted. Let any one wlio doubts this statement, take soil 
free from all organic matter whatever; for example, let him 
mix artificially chemically pure sand, clay, and chalk in the 
same proportions as they exist in the best soils; let him sow 
his seed, and then apply this powerful spirit, and observe the 
results; let him weigh the products, and then he will, beyond 
doubt, see the truth of the fact, that the weight of the crop is 
proportional to the weight of organic matter in the soil. If 
the object of a farmer was merely to obtain good crops for 
a few years, and afterwards to allow the land to lie waste and 
useless, then, indeed, some powerful stimulus, such as the spi¬ 
rit in question, would be of great value; but, what farmer, I 
ask,would so wilfully inj ure his own interest, by thus exhaust¬ 
ing his soil, for the sake of procuring one or two good crops 1* 
Some persons, however, may remark, that it would be ex¬ 
tremely difficult to prove the relation between the organic 
matter in the soil and the crop; for example, they might 
quote the case of turnips, where, in a good crop, two or more 
tons are produced, by a space of ground, upon which not 
more than one ton of farm-yard manure has been spread; and 
nevertheless there is sufficient nourishment left for several 
crops afterwards without any addition. I shall therefore 
shew the manner in which this relation is to be discovered, 
or at least point out some circumstances, which are liable to 
* And yet there are thousands of American farmers who 
are continually pursuing this sinful practice.— Cond. 
be overlooked, but which are of the utmost importance in I 
any investigation of the kind. In the first place, the real 
weight of dry organic matter in a crop is extremely small in 
comparison to the weight of the crop itself; for instance 25 
tons of globe turnips are calculated to contain only two tons 
of solid matter, of which a part of course is saline. Hence in 
that turnip there is not 8 per cent of organic matter. The 
grain crops of course contain a far greater quantity, but even 
in them more than one-fifth is composed of water and saline 
substances. Secondly, the quantity of organic matter in a soil 
is very liable to be underrated; as will be shewn by the fol¬ 
lowing calculation. According to the analysis of Sir Hum¬ 
phrey Davy and others, good soil contains about 11 per cent 
at least of dry organic matter; now, taking nine inches as the 
depth of such a soil (which is by no means great,) it will be 
found by calculation that one imperial acre will contain no 
less than 91 tons of dry organic matter, and hence, were the 
whole capable of being converted into turnips without loss, 
each acre of good soil would (theoretically at least) be capa¬ 
ble of producing upwards of 1290 tons of globe turnips be¬ 
fore the land would be completely exhausted! A careful ex¬ 
amination of these facts cannot fail to shew to all, the fallacy 
of judging of the power of a manure by its effects when mix¬ 
ed with soil. Of course I do not mean by this to dispute the 
value of experiments with different kinds of manure on vari¬ 
ous crops; but merely have endeavored to shew that, when 
authors attempt to talk about concentrating manure to such 
an extent, that the contents of a quart bottle will supply nou¬ 
rishment to the crop upon an acre of land, they should, in the 
first place, prove whether their substance is really a manure, 
or merely a chemical agent; and certainly ought not to give 
publicity to any opinions performed in a manner so replete 
with fallacies. The following fact alone should be sufficient 
to silence at once all such idle propositions. We have every 
reason to believe that “creation has long since ceased and 
conversion alone continues to take place,” or in other words, 
‘‘new matter is never now produced, but merely matter al¬ 
ready existing is constantly changing its form.” Much more 
might be said with reference to this point, but we have sub¬ 
jects of far greater importance to engage our attention, than 
the refuting of such visionary speculations. To recapitulate, 
therefore, the objects to be attained by the application of 
manure may be stated to be, the preservation of a certain 
degree of richness in the soil, in order that the seed sown 
may be furnished during all the stages of its growth, with a 
constant supply of organic matter, in such a form as to be 
capable of being absorbed; and moreover this organized mat¬ 
ter being supplied by otherwise useless, and in fact injurious, 
substances, one of the national advantages of manuring land 
may he said to consist in the conversion of noxious matters 
into useful and wholesome food. 
II. In giving a general account of the composition and re¬ 
spective value of the more important manures, we must re¬ 
member that there are many collateral circumstances to be 
taken into consideration, which, although they may be of no 
importance theoretically, are nevertheless of such great prac¬ 
tical consequence, that, without due attention to them, no 
scientific account of manure can be of any value to the far¬ 
mer. Manures are generally divided into organic and inor¬ 
ganic or mineral .. Professor Low, in his excellent work on 
practical agriculture, adds an intermediate division of mixed 
manures, which will aid greatly the consideration of this ex¬ 
tensive class of substances. Properly speaking, the organic 
and mixed are the only true manures, the purely mineral ones 
acting either as chemical aids by promoting putrefaction; as 
mechanical agents by altering the texture of the soil; or pro¬ 
bably also as stimulants, by acting directly upon the roots of 
the plants themselves. 
I. Organic manures :—By adding organic matter to the soil, 
we are of course supplying plants with all that they require 
for their nourishment; nevertheless it is not sufficient that 
this organic matter should exist in the soil, it must be in such 
a state as to be capable of being absorbed by the roots of the 
plants; for which purpose we have already seen that its ele¬ 
ments must be in that peculiar state of combination which 
has received the name of huniin; or, to expres's it otherwise, 
in such a form as to be rendered soluble in water when ex¬ 
posed to the action of the spongioles. From this fact we may 
make several generalizations with reference to the respective 
value of different kinds of organic manure. Th us scientifically 
speaking, a manure may be said to be valuable in direct pro¬ 
portion to the quantity of pure organic matter it contains, its 
tendency to decomposition, and its facility of being rendered 
soluble by this, and other changes which take place in it; 
practically, however, a manure may be said to be valuable in 
direct proportion to the length of time during which its influ¬ 
ence is felt by the crops on the land to, which it is applied: 
as also to its portability, to the facility with which it can be 
incorporated with the soil, and, last not least, to its cheapness 
and the readiness with which it can be procured. Hence tffe 
most useful manure would be one which combined these 
several advantages, namely,one which was cheaply produced, 
easily carried, readily mingled with the soil, and when there, 
keeping up, by its gradual decomposition, a steady supply o£ 
humin, or other soluble organic matter. To discover such a 
manure, or, still better, to ascertain some method of imparting 
such properties to the manures in common use, would be one 
ofthe most valuable acquisitions to modern husbandry. That 
chemistry may in time be capable of doing this, there is little 
reason to doubt, all that seems, necessary, being, that some 
person properly qualified shdhld earnestly devote himself to 
the task. In the followir% remarks upon the nature and 
composition of the different ^lecies of manure, particular at¬ 
tention will be paid to these qualifications. For the sake of 
perspicuity I shall subdivide that class of organic manures in¬ 
to the purely vegetable, the purely animal, and the vegeto-am- 
mal. 
(1.) The purely vegetable manures are, green plants, rape- 
cake, malt-dust, the steepings of the flax and hemp, straw, 
woody fibre, tanners’ spent bark, &c. 
Green plants are constantly used as manure, and are very 
useful for that purpose; they are seldom collected expressly, 
but are made use of on the spot where they grow; as exam¬ 
ples of this, we may mention the ploughing in of grass, and 
the ploughing and hoeing of weeds during fallow and green 
crops. This manure consists chiefly of saccharine and muci¬ 
laginous matters mixed with ligneous fibre; and it conse¬ 
quently will be observed that it requires no preparation what¬ 
ever; that it contains organic matter already in a soluble 
i state, namely the sugar and gum, and the ligneous fibre itself 
1 is so moist and so completely impregnated with vegetable 
juices, that fermentation rapidly commences, and consequent- 
i ly a supply of soluble matter will be kept up until tlie whole 
is consumed. Care must be taken, however, in ploughing in 
green crops for manure, not to make too deep a furrow, especi¬ 
ally on strong lands; as in that case the quantity of soil which 
covers the vegetable matter is so thick that it diminishes the 
action of the air, &c. upon it; and it is a well ascertained 
fact, that fermentation is retarded, if not altogether prevent¬ 
ed, by compression and the exclusion of air. The best period 
for ploughing in green crops (provided other circumstances 
permit of it,) is undoubtedly when the plants are in flower, 
as at this period tliay contain the greatest quantity of sugar 
and mucilaginous matter; and, moreover, in the instance of 
weeds, it prevents the possibility of their propagating their 
species by the scattering of their seed. The importance of 
allowing this species of manure to ferment in the ground, in¬ 
stead of in a heap, is, that (in addition to the great saving of 
labor) the slowness with which the decomposition takes 
place, is supposed to tend to produce much more soluble mat¬ 
ter and less gas than when it proceeds above ground. The 
parings at hedge roots, scourings of ditches, pond-weeds, &e. 
may be used in this manner. 
Rape-Cake has been used with great success as a manure- 
this, like the preceding, contains a large quantity of vegetable 
matter, already in a state capable of being dissolved in water, 
its .composition being mucilage, a large quantity of vegetable 
albumen, a little oil, and woody fibre. It has the advantage 
over the former of being much drier, and hence containing 
far more manure in the same bulk of material; but, on the 
other hand, it is by no means so easily procured, and is 
much more costly. It is chiefly used in fallow, before wheat, 
and should be sown fresh; and before its application, should 
be kept as dry as possible, as moisture readily causes fermen¬ 
tation to commence.which,when once set in, will undoubtedly 
proceed with rapidity, unless the substance is carefully dried. 
And here we may make the general remark, that all sub¬ 
stances which contain much fluid, and more especially such 
as are composed of mucilage, sugar, and other soluble mat¬ 
ters, should be used when perfectly fresh. 
Malt-Dust is mentioned by Sir Humphrey Davy as a good 
manure, on account of the quantity of sugar it contains. I 
have not, however, been enabled to meet with any particular 
account of its application; of course, if used, it should be al¬ 
lowed to ferment in the soil. The washings and other refuse 
of distilleries, I am informed, are much used in some parts of 
Ireland, as an application to grass lands, and their effects are 
stated to be very powerful. This, of course, will depend upon 
all the vegetable matter which it contains being soluble, and 
therefore very probably absorbed at once, without undergoing 
any decomposition whatever. 
The next manure we shall mention, is one which can be ap¬ 
plicable in a few cases only, on account of the local nature of 
its production; we refer to the water in which the fiax and hemp 
have been steeped. It is well known that flax and hemp con¬ 
sist of tlie woody fibres of these plants, and that one of the 
first steps in their manufacture is the steeping of the plants 
in water, in order that the softer tissues may ferment, and the 
ligneous fibre be thus freed from tlie useless parts of the ve¬ 
getable; of course, therefore, the water in which these plants 
have been steeped, becomes fully charged with soluble and 
putrescent vegetable matter, and consequently acts powerful¬ 
ly as a manure, and moreover requires no preparation what¬ 
ever, as fermentation has already commenced. It is not ne¬ 
cessary, however, to dwell much upon this subject, as its use 
must, of course, be confined to those districts where fia-x and 
hemp are cultivated. 
Sea-weeds .—All sea-shore plants, especially those which 
grow below highwater mark, and which belong to the natu¬ 
ral families of Alga, and Fad, <fcc. contain more or less mi¬ 
neral alkali (carbonate of soda,) and have long been used as 
manure by the farmers in the neighborhood of the sea. 
They are, however, so succulent and mucilaginous, that their 
effects are by no means lasting; even when placed in heaps 
and allowed to ferment, they produce but very little heat; in, 
fact, appear rather to dissolve aw r ay. They consist chiefly of 
water, mucilage, a small quantity of woody fibre, and saline 
matter; according to the analysis of Sir Humphrey Davy, 
nearly four-fifths was water, which contained no ammonia, 
and consequently the plants possess no azote. When applied 
to land, their effects are felt almost immediately, as the 
mucilage dissolves as soon as the outer covering of the 
plants is destroyed by fermentation; but from its soluble na¬ 
ture, its effects are but slight, and after the first year, are no 
longer perceptible. The alkali they contain must also act as 
a chemical solvent, which will hasten their consumption. It 
has been proposed, (see vol. iii. of this Journal, 1831-2,) to 
collect the sea-ware, and dry it by spreading it like hay, by 
which means, of course, nothing but water will be lost, and 
at the same time, the bulk will be reduced to one-fifth, in 
which state the author considers it to be a very valuable ma¬ 
nure, and calculates that it can be procured and carted off at 
half the price of straw. This suggestion, I think, might pro¬ 
bably be useful in some of the farming districts which are si¬ 
tuated near the sea, but still not close enough to use the ware 
in its fresh state, as undoubtedly the manure is a good one as 
long as it lasts. The drying, also, will prevent the decom¬ 
position from taking place so rapidly as if applied when 
fresh. 
Dry straw of wheat, barley, and other grain crops, and 
spoiled hay, are always useful manures. Sir Humphrey Da¬ 
vy, in speaking of these, adheres to the opinion which per¬ 
vades the whole of his work upon Agricultural Chemistry, 
namely, that they should be applied fresh, and that if allow¬ 
ed to ferment, a large quantity of nutritious matter is lost. 
As this is a point more severely criticised than any olher 
statement which his work contains, and as, moreover, it is 
one of extreme importance, I shall here enter fully into the 
subject, and endeavor to reconcile, if possible, the exceed¬ 
ingly discordant opinions which are entertained regarding it. 
To proceed, let us state the question. Theorists say all 
manures should be applied to the soil as fresh as possible, be¬ 
cause, during the process of fermentation, if allowed to pro¬ 
ceed above ground, much valuable matter is lost which would 
otherwise have been available to the crops. Practical fanners, 
on the contrary, maintain, that experience has proved to them, 
that, unless the manure is fermented to a certain degree be¬ 
fore it is applied, it is not of half the value; in fact, in many 
