| |
| of the last | ... | 3.0 | 0.24 | ... | ... |
|Sandy soil, long | | | | | |
| after manuring |Trefoil | 7.6 | 0.74 | 19.02| 80.24 |
| Do. Recently | | | | | |
| manured | ... | ... | 0.85 | 19.41| 79.74 |
| Do. manured 8 | | | | | |
| days before | ... | ... | 1.54 | 18.80| 79.66 |
|Heavy clay |Jerusalem | 7.0 | 0.66 | 19.99| 79.35 |
| | artichoke | | | | |
|Fertile soil (moist)|Meadow | 5.5 | 1.79 | 19.41| 78.80 |
+--------------------+------------+---------------+--------+--------+---------+

From these analyses it appears that the air contained in the pores of
the soil is much richer in carbonic acid than the atmosphere, the
poorest soil containing about 25 times, and a recently manured soil 250
times as much. This carbonic acid, which is obviously produced by the
decomposition of the vegetable matters and manure, acting partly as gas
and partly dissolved in the soil water, exerts a solvent action on its
constituents. And, though a very feeble acid, its continuous action
produces in the course of time a large effect; while, during the
interval, the constituents of the soil are safely stored up, and
liberated only as the plant requires them, by which bountiful provision
of nature they are exposed to fewer risks of loss than if they had been
all along in a state in which they could be absorbed. Carbonic acid not
only assists in effecting the decomposition of the minerals of the soil,
but its aqueous solution acts as a solvent of many substances, which
are quite insoluble in pure water. It is in this way that much of the
lime contained in natural waters is held in solution, and it has been
ascertained that magnesia, iron, and even phosphate of lime, may also be
dissolved by it. It is probable that when these substances are
dissolved, the plants will take them from solution in place of
themselves attacking the insoluble matters; but of the extent to which
this may occur nothing is yet known--the action of solvents on the soil
being a subject which is as yet scarcely examined.

Carbonic acid is, however, a most important agent in produ