Encyclopaedia Britannica, or, a Dictionary of arts, sciences, and miscellaneous literature : enlarged and improved. Illustrated with nearly six hundred engravings > Volume 1, A-AME

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Manures- properties of niariufe, It alfo, by its mechanical quali-
' ties, renders the foil more permeable to Water and to
the roots of the plants, and is thus favourable to the
progrefs of vegetation. At the fame time, as the earths
themfelves have a chemical a6tion upon water, and are
capable of affording a proper bafs for plants, he confi-
ders them as in many cafes fufficient to promote vegc-
' tation. Upon thefe principles, M. Parmentier takes a
view of different fubflances ufed as manures.
Marl, in his opinion, is capable of acting in the
fame manner as the molt fertile foil,- when the princi¬
ples of which it is compofed, namely, clay, fund, cal¬
careous earth, and magneiian earth, are juilly propor¬
tioned to each other. But it is fometimes compact and
tenacious, becaufe it contains a fuperabundant portion
of clay, and at other times porous and friable, becaufe
it contains too much land) and therefore is not in ge¬
neral fit for vegetation by itfelf. Thefe confiderations
ought always to be our guide when we mean to employ
marl as a manure.
It has been fuppofed that to marl is a fort of tech¬
nical exprefiion, intended to denote the bringing toge¬
ther or dividing the earthy particles by means of clay
or land. It appears to our author, that neither of the
above operations can properly be called marling; be¬
caufe, in either cafe, all we do is, to put the foil into a
fituation to receive and to profit by the influence of the
atmofphere, and that of the manures made ufe of. The
peculiar principle of marl is, that part of it which, like
lime, a6ts very powerfully upon the different aeriform
fluids, is eafily reduced to powder, eft’ervefees with a-
cids, and fends forth a quantity of air-bubbles Avhen wa¬
ter is poured upon it. Now this matter, which in a
particular manner does the office of manure, refides
neither in clay nor 4n fand. Upon the proportion of it
-depends the duration of the fertility it produces ; con-
fequently it is of importance, when we make ufe of
marl, to know which of its conifituent parts it contains
in the greateft proportion, otherwife in fome cafes we
ihould only add one common kind of earth to another.
Hence our author infers, that for a chalky foil clay is
the proper manure, and that in fuch a foil a clay bot¬
tom is of more value than a gold mine.
“ Wood-allies, as a manure, may be, in fome refpects,
compared to marl y at leaft they contain the fame earths
as thofe which generally enter into the compofition of
marl, but they contain a greater quantity of faline fub-
1 lances, proceeding from the vegetables of which they
wre the refidue, and from the procefs made ufe of in
their combuftion ; a procefs which inereafes their acti¬
vity, and Ihould render us careful in what manner and
for what purpofe we employ them. Wood-alhee,
when fcattered over fields, at proper times and in pro¬
per quantities, dellroy weeds, and encourage the vege¬
tation of good plants. But do the allies produce this
effect by a fort of corrolive power? I cannot (fays our
author) thirtk it •, for in that cafe all kinds of plants
would indiferiminately be acted upon by them, and to
a certain degree dellroyed. '
“ Befides, the allies of frelli wood are feldom em¬
ployed until they have been lixiviated ; in which Hate
they are deprived of their cauftic principle} thofe allies
which are moll commonly made ufe of for manure are
produced either from wood that has been floated in Ava-
Pradtice.
ter, or from turf, or from pit-coal, and contain little Manures,
or no alkaline fait. ......
“ It appears much more probable that allies, when
laid upon ground, dellroy the weeds by a well known
effect, namely, by feizing with eagernefs that moillure
Avhich ferved to produce thole weeds, and which in a
fuperabundant quantity is neceffary to their exillence
and fupport. W hereas thofe plants which have a firmer
texture and a longer root, which are rendered Itrong
by age and by haA ing Avithllood the rigour of winter,
and Avhich are in fact the plants of which the fields are
compofed, do not fuller any damage from the applica¬
tion of the allies ; but, on the contrary, by being freed
from the fuperfluous Aveeds Avhich Hilled them, and rob¬
bed them of a part of their fullenance, they receive a
quantity of nourilhment proportioned to their wants.
The Hate of relaxation and languor to which they Avere
reduced by a fuperabundance of Avater, leaves them, the
foil gets its proper confiHence, and the grafs, corn, &c»
acquiring the Hrength and vigour which are natural to
them, foon overcome the mofs, rallies, and other weedsy
thus a good crop, of Avhatever the field confiffs of, is
produced. It is in the above manner that Avood allies
ad, Avhenever in the fpring it is neceffary to apply
them to meadows, corn fields, &c. the plants of Avhich
are Hilled arid Aveakened by a luxuriant vegetation of
Aveeds, the ufual confequence of mild and Avet Avinters.
“ When Avood allies produce an effed different from
what is above deferibed, it is either becaufe they hap¬
pen to contain too much alkaline fait, or that they are
laid on the ground in too great quantity, or that the
fields to Avliich they are applied Avere not fulficientlv
wet to reHrain their adion ; for Avhen they are fcatter¬
ed upon cold foils, and buried by the plough before
the time of foAving, they are, like lime, of great fer-
vice. The laff mentioned fubHance is very efficacious
in other circumHances •, and there is a Avell knoAvn me¬
thod of ufing it pradifed by the Germans, as folloAvs :
A heap df lime is formed by the fide of a heap of poor
earth, and Water is poured upon the lime ; the earth
is then thrown over it, and becomes impregnated with
the vapours Avhich efcape from the lime Avhile it is
flaked. The earth, after being thus aerated, may be
feparated 5 and although no lime remains mixed with
it, is, by the operation jull deferibed, rendered capa¬
ble of giving a luxuriant vegetation to Avhatever plants
may be put into it.
“ It is pollible, therefore, to aerate earth as Avell as
fluids •, for this ptirpofe, by mixing it Avith certain fub-
Han'ces during their decompofition, Ave muff attach to
it the principles of which thofe fubffances are compo-
fed j from Avhich there x*efults a matter fo loaded with
gas, as to form a more compound fubHance, and one
Avhich has acquired neAV properties. The Arabians, for
example, Avho take great pains to improAre their land,
are accuffomed to make large pits, Avhich they fill Avith
animals which happen to die : thefe pits they after-
Avards Cover Avith calcareous or clayey earth j and after
fome time thefe earths, Avhich of themfelves are Herile,
acquire the properties of the richeff manures.
“ The foregoing obfervations may at leaff be confi-
pered as proving, that thofe fubffances which, Avhen
employed frelli and in too great quantity, are moff pre¬
judicial to Aegetation, have, on the contrary, an advan¬
tageous
AGRICULTURE,