uch soils, are killed out, and the more
nutritive grasses are allowed to flourish instead. The action of lime in
promoting the formation of a class of compounds of great importance in
the soil--viz., hydrated silicates--is worthy of notice. According to
the commonly accepted theory, much of the available mineral fertilising
matter of the soil is retained in the form of these hydrated silicates.
Hence lime, by increasing these compounds, not merely adds to the amount
of the available fertility in the soil, but also increases its
absorptive power for food-constituents.

III. BIOLOGICAL ACTION OF LIME.

The last way in which lime acts is what we have termed biological. By
this we mean the important _role_ lime plays in promoting or retarding,
as the case may be, the various kinds of fermentative action which go on
so abundantly in all soils. The presence of carbonate of lime in the
soil is a necessary condition for the process of nitrification. Lime is
the base with which the nitric acid, when it is formed, combines; and as
we have seen, when discussing nitrification, soils of a chalky nature
are among those best suited to promote the natural formation of
nitrates. This is one of the reasons for the beneficial effects produced
by lime when applied to peaty soils. Not merely does it help to
decompose the organic matter so abundant in such soils, but it also
furnishes the base with which the nitric acid may combine when it is
formed. But while the action of lime is to promote fermentation, it must
not be forgotten that there may be cases in which its action is rather
the reverse of this. Fermentation of organic matter goes on when there
is a certain amount of alkalinity present; while, on the other hand, the
presence of acidity seems to retard and check it. Too great an amount of
alkalinity, however, would, in the first instance, retard fermentation
as much as too great acidity. It has been claimed that the addition of
caustic lime to fresh urine may act in this way; and if this were so,
the addition of lime to farmyard manure might, to a certain extent, be
defended. The experiment, however, would be a hazardous one and not to
be recommended, as loss of ammonia would most likely ensue.

_Action of Lime on Nitrogenous Organic Matter._

The action of lime on nitrogenous organic matter is of a very striking
kind, and is by no means very clearly understood. As we have pointed
out, it sometimes acts as an antiseptic or pre