Chlorine in the soil is probably always in an available condition.
Oxide of iron exists, as has been previously stated, usually in the form of the peroxide (or red oxide). Sometimes, however, it exists in the form of the protoxide (or black oxide), which is poisonous to plants, and renders the soil unfertile. By loosening the soil in such a manner as to admit air and water, this compound takes up more oxygen, which renders it a peroxide, and makes it available for plants. The oxide of manganese is probably of little consequence.
The usefulness of all of these matters in the soil depends on their exposure; if they are in the interior of particles, they cannot be made use of; while, if the particles are so pulverized that their constituents are exposed, they become available, because water can immediately attack to dissolve, and carry them into roots.
What is one of the chief offices of plowing and hoeing?
Is the subsoil usually different from the surface soil?
What circumstances have occasioned the difference? In what way?
This is one of the great offices of plowing and hoeing; the lumps of soil being thereby more broken up and exposed to the action of atmospheric influences, which are often necessary to produce a fertile condition of soil, while the trituration of particles reduces them in size.
SUBSOIL.
May the subsoil be made to resemble the surface soil?
May all soils be brought to the highest state of fertility?