Ar/ricuJtural Chcnnstry. 
operations of the farm, in which is found all but the first of the 
following sentences ; this one immediately preceding that special 
chapter : — 
From the preceding part of this chapter it will be seen that fallow is that 
period of culture wlien the laud is exposed to progressive disiutegration hy the 
action of the weather, for the purjwse of Uheratincj a certain, quantitij of 
alkalies and silica to he absorbed by future plants. 
" The careful and frequent working of fallow-land will accelerate and 
increase its disintegration : for the purposes of culture it is quite the same 
whether the land be covered with weeds, or with a plant which does not 
extract the potash from the soil." — ith Edition, p. 127. 
Speaking of the mechanical operations of the farm, he says : — 
" Their action consists in accelerating the weathering or disintegration of 
the soil, and thus offers to a new generation of plants their necessary mineral 
constituents in a form fit for reception." — ith Edition, p. ]30, 131. 
" We renew the surface of the soil and endeavour to make every particle 
of it accessible to the action of carbonic acid and oxygen. Thus we procure a 
new provision of soluble mineral substances which are indispensable for the 
nourishment and luxuriance of a new generation of plants." — ith Edition, 
p. 132. 
And again: — 
"Fallow, in its most extended sense, means that period of culture during 
which a soil is exposed to the action of the weather, for the purpose of enrich- 
ing it in certain soluble ingredients. In a more confined sense, the time of 
fallow may be limited to the intervals in the cultivation of cereal iilants ; for 
a magazine of soluble silicates and of alkalies is an essential condition to the 
existence of such plants.*' — ith Edition, p. 1.32, 133. 
"The mechanical operations of the farm, fallow, the application of lime, 
and the burning of clay, unite in elucidating the same scientific principle. 
They are the means of accelerating the disintegration of the alkaline silicates of 
alumina, and of supplying to plants their necessary constituents at the com- 
mencement of a new vegetation." — ith Edition, p. 136. 
Now, falloiD would generally be applicable to land after its 
agricultural exhaustion by the growth of a series of crops, and as 
a preparation for the growth of a succeeding crop of grain- — and 
we maintain, that in 99 out of 100 such cases, in ordinary culti- 
vated lands, mineral manures would not adequately raise the pro- 
duce, whilst the application of amrnoniacal salts or nitrate of soda 
would certainly do so ; — we cannot imagine, tlierefore, that the in- 
crease in produce in such a soil bij fallow, can be measurable by the 
amount of mineral constituents liberated by the chemical action 
of the atmosphere on the soil. We fully grant, indeed, that such 
action — such liberation of mineral constituents — does take place 
during fallow ; but we maintain, that there would be no adequate 
increase of produce, unless at the same time there were a con- 
densation of available nitrogen from atmospheric sources within 
the soil itself, and that it is by the amount of this accumulation of 
available atmospheric food of plants within the soil, rather than by 
the amount of liberated soil-proper constituents, that the increased 
produce of grain will be measurable. 
