be
found in the quantity applied, the nature of the soil, the crop to which
it is applied, and the conditions under which it is applied--_i.e._,
whether it is applied alone or along with other manures.

_Mechanical Action on Soils._

In the first place, it must be noted that salt exerts a mechanical
action on the soil of a very similar kind to that exercised by lime.
When applied to clay soils it causes a flocculation or coagulation of
the fine clay-particles, and thus prevents the soil from puddling to the
same extent as would otherwise be the case. In fact, an example of this
action of salt when in solution causing the precipitation of fine
suspended clayey matter, is afforded by the formation of deltas at the
mouths of rivers. The power of clarifying muddy water is common indeed
to saline solutions. Schloesing attributes the clarifying power of a
soil to the presence of the saline matters it contains; and from this
point of view it would appear that manures containing any saline
substance may exert an important mechanical influence on the soil.

_Solvent Action._

But a much more important property of salt is its solvent action on the
plant-food present in the soil. Its action in decomposing the minerals
containing lime, magnesia, potash, &c., is similar to the action of
gypsum. By acting upon the double silicates it liberates these necessary
plant-foods. It is not only on the basic substances upon which it acts,
but also on the phosphoric and silicic acids, which it sets free. Its
power of dissolving ammonia from the soil is considerable. Experiments
with a weak solution of salt on a soil by Peters and Eichhorn to test
its solvent power, showed that the salt solution dissolved more than
twice as much potash and nearly thirty times as much ammonia as an equal
quantity of pure water did. When applied to the soil, it seems chiefly
to liberate lime and magnesia. The exact nature of the chemical action
taking place is a point of some dubiety. According to some, it is
changed into nitrate of soda; according to others, into carbonate of
soda. The latter theory seems to be the more probable one. Its action on
the lime and magnesia compounds is to convert them into chlorides; and
this chemical reaction explains the action that salt has in increasing
the water-retaining and water-absorbing power of the soil; for the
chlorides of magnesia and lime are salts which have a great power of
attracting water from the air.