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the soils are partly composed o fth e fragments of any of the ha,rdcr rocks, ns those fine
particles of stone, being acted upon by the atmosphere, are constantly decomposing aud
liiriiishing tho sod with potash, soda, and vai-ions saline substances. “ The soluble salts
tormod in this manner,” Professor SoUy observes, “ arc dissolved by tho rains and in
great part washed .way from the surface; a portion, however, always remains in th o
soil, aud IS absortcd by plants. When a crop of some plant requiring, for example a
largo quantity of potash, IS raised in such a soil, it often happens that the crop takes
away nomly all the soluble potash the soil coutains ; and, inconsequence, it would bo
impossible to raise a second crop of that plant on the same soil, as there would not bo
potash enough in it. If, however, the soil is left for some time M ow , if no crop at aU
IS raised on it the sod has túne to renew itself, by the action of the afr, the fiu-thcr decomposition
of the silicates, and other simüai- stony compounds in the soil, is effected, and
a fresh supply of potash is provided.” {Solly’s Chemistry, 2nd edit, p. 168.)
S dbsect. 4. Alteration o f the constituent Parts o f Soils.
1222. Soils may be altered by the addition or subtraction o f ingredients in which they
ai-c dohcicnt or siiperabouud, and by the chemical change of some of thcir constituent
part or p.arts by the action of fire. euiibiiiuuit
1223 In ctacertaining the composition o f fa u lty soils, with a view to their improvement lu
adding to their constituent parts, any particulai' ingredient the w.ant or excess of which is
the cause of their iinproductiycncss should bo piu-ticiilarly attended to ; if possible, they
should be comgired with fertile soils in the same nciglibourliood, and in similar ktua-
tions, as the difl'ereiice of the composition may, in many cases, indicate the most proper
methods of improvement If, on washing a sterdo soil, it is found to contain an o x is s
o the salts of n-on, or any acid matter, it may b e ameliorated b y th e application of
qmcklime. A sod of good apparent texture, containing too great a proportion of sulphate
of iron, wm be sterde; but the obvious remedy is a top-dressing with lime, wliich
converts the sulphate into manure. I f there be an excess of calcareous matter in the
Z t a b lL L 1 ? “7 f « application of sand or clay. Soils too abundant in sand
aio beneflted by the use of clay, or marl, or vegetable matter. Light sands ai'e often
benehted by a dressing of peat, and peats by a dressing of sand ; though the former is
111 Its nature but a temporary improvement. Wlicn peats are acid, or contain fcrniei-
noiis salts, calcareous matter is absolutely neeessary to bring them into cultivation. Tire
be,St natm-al sods are those of which the materials have been derived fi-om difFci'ciit
stiata, which have been minutely divided by afr and water, and are intimately blended
together ; and in improving sods artiflcially, the cultivator cannot do better than imitate
tJie processes of natm-e.
1224. The alterations made in soils by the addition o f other earths, must, of oonrsc, bo
L Z iL fflffLm s"ods“ ’“ ft™*’ ' ' “ ft“ “ *° “ ft “ ‘“ ft
1225. Incineration, The ohcmioal changes which can he effected in soils by biirnino-
the sm-face .ai-o considerable. This practice was known to tho Eomans, is more or lc £
T -Z™' 1 U“ 0P“> 1® mentioned as au approved pi-actico by om- oldest
agiicultnral ivritcra, and has lately excited some dogreo of attention from the succcssfid
experiments of different cultivators.
1226. Clayey soils are most improved by burning. “ Many of the silicates of alumina ”
id r t e Z l r i ' t ' ' 7 T ‘'fr*«®'?'“* “ft***® “ ‘**p etc solubdity when they are previously melted by heat. Tfto" this class® foof‘ Cs’i l«icca<tle™s 'cb ecloomngpipe
and potters clay loam, and the different vai'icties of clay occiii'ring in soils. In
the natmta state of clay, it may be digested with concentrated siilijhuric acid for liom-s
without dissolving in any appreciable quantity ; but when the clay is slightly hiimt (a!
IS done, for example, m several alum works), it dissolves in acids with great ease while
the sihca IS separated m its gelatinous and soluble foi-m. Common potter's clay forms
p n c iaU y v e ry sterde sods, althoiigb it contains within it all the conditions for tho
luxunant growth of'plants ; but the mere presence of these conditions does not suffice
to render them useful to vegetation.” {liebig’s Chemistry, 4th. cd.. p. 135.) When
however, sods of this nature are sufficiently pulverised to render them accessible to air
s ; ^ r sZ M Z g e S t a Z . ft“ °""®'ft"’ ft”'“ft“ ft "ft“ ’ ‘“ft “‘“ft' ft*ft“ ft"‘® "ftftft®-
1227. Calcareous soils are dso gcncraUy improved by bm-ning. Soil that is formed
of pm-ecai-bonateof limo is ban-eil and unfruitful, but when Lixed with sand and a
httle clay, it forms a calcareous loam. I f calcai-cous loam, or even pure cai'bonatc of
ir f f tin Z sZ Z tl ft"*’?.™ ? f r f TPcfrcfr from it i ««fr if exposed to the atmosphci-e
111 tins state, the piu'o lime which it contains rapidly reabsorbs from tho air tho carbon
w hich was expelled froni it by biinimg, in the fomi of carbonic acid gas, cnimbUng down
at the same tune into a fine powder, so as to become intimately mixed with the soil.
^ 1228. The new red sandstone or red marl is also greatly improved by biiming as
macccl, arc all suils of a marly, clayey, or calcareous texture. ’
1229. When the surface o f peat lands," Morton observes, “ is pared off and burnt
and pulverised by the influence of tlic frost, it becomes a soft black soil, composed
eiitii'oly of vegetable matter with oxide of iron and the tannin principle iiitimatclv
blended throiigli the mass ; ” and when this is mixed with clay it becomes one of the
“ most productive of all soils.” {Morton on the Nature and Property o f Sails, p. 19 )
^ 1230. The advantages o f burning are, that it renders the soU less compact, loss tenacious,
and less retentive of moisture ; and, when properly applied, may couvert a matter
■which was stiff, damp, and, in consequence, cold, into one, powdery, dry, aud warm
and permeable by air and water. ’
1231. The great objection made by speculative chemists to paring and burning is, that
they destroy tho vegetable and animal manure which may exist in the soil : but in cases
in which the texture of its earthy ingredients is permanently improved, there is more
than a compensation for this temporary disadvantage ; and in some soils where there is
an excess of inert vegetable matter, the destruction of it must be beneficial, as the cm--
bonaceous matter remaining in the ashes must be more useful to the crop than the
vegetable fibre from which it was produced. Burning also improves aU soils containin«»-
clay, by mcrcasmg thcir power of absorbing and condensing from the air ammonia,
carbonic acid, and other gases necessary to the gi-o^wtli of plants.
1232. The soils improved hy burning are all such as contain too much dead vegetahlo
libre, and which consequently lose from one third to one half their weight by incineration
; and_ all such as contain their earthy constituents in an impalpable state of division,
i. e. tlie stiff clays and marls, arc improved by burning : but in coarse sands, or rich
sofis containing a just mixtiu-e of tho cai-ths, and in all cases in wliich the texture is
suificicntly loose, or tlie organisable matter sufficiently soluble, the process of torréfaction
cannot be useful.
Subsect. 5. Changing the Condition o f Lands in respect to Water.
1233. The water ofth e soil where superabundant may be withdrawn, and when deficient
supplied: these operations with water are independent of its supply as a maniu-c, or as
affording the stimulus of heat or cold.
1234. Stagnant water may be considered as injurious to all land plants, by depriving
them of a sufficiency of atmospheric air, and thus diseasing thcir roots and submerged
parts. Wliere the surfacc-soil is properly constituted, and rests on a subsoil moderately
porous, both will hold water by capillary attraction ; and what is not so retained, will
sink into the interior _ strata by its gravity; but where the subsoil is retentive, it will
resist, or not admit ■\vith sufficient rapidity, the percolation of water to the strata below,
which accumulating in tho surfacc-soil till its proportion becomes excessive as a component
pai-t, not only can-ies off the extractive matter, but diseases the plants. Hence tho
origin of surface-draining, that is, laying land in ridges or beds, or intersecting it with
small open gutters.
1235. Springs. Where the upper stratum is porous in some places, and retentive in
others, and on a retentive base, the water, in its progress along the porous bed or layer,
will be interrupted by tho retentive places in a gi-cat ■s'ariety of ways, and there accu-
miilating will bm-st thi'ough the upper surface in the form of springs, which ai-e more
injurious than surface-water, as being colder, and generally pci-manent in thefr operation.
Hence the origin of under-di-aiuing in all its varieties of collecting, extracting, and conveying
water.
1236. The water o f rivers may become injurious to lands on thcir banks, by too frequently
overflowing their surface. In this case, the stream may be included by mounds
of cai-th 01- other materials impervious to water ; and thus aquatic soils may be rendered
di-y and fit for useful herbage and ai-ation. The same may be said of lands occasionally
ovci-flown by the sea. Hence the origin of embanking, an art earned to a great extent
in Holland and Italy. (Sec Smeaton's Posthumous Works; Sigismondi Agr. Tosc.;
Paccolta dei Autori che trattano dell’ Ague; and our ai-ticle Embankment in Supv. Encvc.
Brit. 1819.) ^ i i J
1237. Iirigation, like aeration, acts in two ways—mechanically and chemically, tliough
foimcrly many chemists supposed it to have only mechanical action.
1238. The mechanical action o f irrigation is, that it softens the soil and preserves tho
roots of plants in a healthy state. I t also sei-vcs to dissolve the various earthy matters
contained in the soil, and acts as a medium by wliich they arc taken up into the plants.
“ Very dry pai-chcd land,” observes Professor SoUy, “ is, of com-sc, improved by im g a tion,
when from the heat of the climate the greater prn-t of the natm-al moisture of the
soil is evaporated. Under such cfrcurastanccs, the artificial application of water is
iicccssai-y for the successful cultivation of plants, and accordingly it is a constant part