le organic, or animal and vegetable, manures,
(especially when applied, as is usual, in an incompletely fermented
condition,) absolutely require fresh supplies of atmospheric air, to
continue the decomposition which alone can prepare them for their proper
effect on vegetation.

If kept saturated with water, so that the air is excluded, animal manures
lie nearly inert, and vegetable matters decompose but
incompletely,--yielding acids which are injurious to vegetation, and which
would not be formed in the presence of a sufficient supply of air. An
instance is cited by H. Wauer where sheep dung was preserved, for five
years, by excessive moisture, which kept it from the air. If the soil be
saturated with water in the spring, and, in summer, (by the compacting of
its surface, which is caused by evaporation,) be closed against the
entrance of air, manures will be but slowly decomposed, and will act but
imperfectly on the crop,--if, on the other hand, a complete system of
drainage be adopted, manures, (and the roots which have been left in the
ground by the previous crop,) will be readily decomposed, and will
exercise their full influence on the soil, and on the plants growing in
it.

Again, manures are more or less effective, in proportion as they are more
or less thoroughly mixed with the soil. In an undrained, retentive soil,
it is not often possible to attain that perfect _tilth_, which is best
suited for a proper admixture, and which is easily given after thorough
draining.

The soil must be regarded as the laboratory in which nature, during the
season of growth, is carrying on those hidden, but indispensable chemical
separations, combinations, and re-combinations, by which the earth is made
to bear its fruits, and to sustain its myriad life. The chief demand of
this laboratory is for free ventilation. The raw material for the work is
at hand,--as well in the wet soil as in the dry; but the door is sealed,
the damper is closed, and only a stray whiff of air can, now and then,
gain entrance,--only enough to commence an analysis, or a combination,
which is choked off when half complete, leaving food for sorrel, but
making none for grass. We must throw open door and window, draw away the
water in which all is immersed, let in the air, with its all destroying,
and, therefore, all re-creating oxygen, and leave the forces of nature's
beneficent chemistry free play, deep down in the ground. Then may we hope
for the full bene