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of it is lost to the soil in which it was formed, and 
dissipated in the atmosphere. 
The action of the sun upon the surface of the 
soil tends to disengage the gaseous and the volatile 
fluid matters that it contains ; and heat increases 
the rapidity of fermentation : and in the summer 
fallow, nourishment is rapidly produced, at a time 
when no vegetables are present capable of absorb- 
ing it. 
Land, when it is not employed in preparing food 
for animals, should be applied to the purpose of 
the preparation of manure for plants ; and this is 
effected by means of green crops, in consequence 
of the absorption of carbonaceous matter in the 
carbonic acid of the atmosphere. In a summer’s 
fallow a period is always lost in which vegetables 
may be raised, either as food for animals, or as 
nourishment for the next crop ; and the texture of 
the soil is not so much improved by its exposure 
as in winter, when the expansive powers of ice, the 
gradual dissolution of snows, and the alternations 
from wet to dry, tend to pulverize it, and to mix its 
different parts together^ 
In the drill husbandry the land is preserved clean 
by the extirpation of the weeds by hand, and by 
raising the crops in rows, which renders the de- 
struction of the weeds much more easy. Manure 
is supplied either by the green crops themselves, 
or from the dung of the cattle fed upon them ; and 
the plants having large systems of leaves, are made 
to alternate with those bearing grain. 
It is a great advantage in the convertible system 
of cultivation, that the whole of the manure is em- 
Y 
