be added that the slag used in these
experiments was rich in phosphoric acid, and was in an unusually fine
state of division. Experiments carried out by the author have proved
slag to be, on various Scottish soils, one of the most economical
phosphatic manures to apply to turnips.[239]

We will sum up, in conclusion, the deductions which may be fairly drawn
from the results of all the above-mentioned experiments as to the value
of basic cinder as a manure.

_Soils most suited for Slag._

Although its action is undoubtedly more favourable on some soils than
others, it may be broadly stated that generally its phosphoric acid is
_half as valuable_ as that in soluble phosphate. The soils on which it
will have the most marked effect will be those of a _peaty_ nature,
_poor_ in lime, but _rich_ in _organic matter_. The beneficial results
obtained by an application of lime to peaty soils are well known. As the
slag contains a large percentage of free lime, it thus performs on such
soils a double function. On meadow-lands, all kinds of pasture-lands (if
not of too dry a character), and clay soils poor in lime, its action has
been shown to be especially favourable. Of different kinds of crops,
those best suited to benefit from the slag as a phosphatic manure are
those of the leguminous kind. This arises from the fact that their
period of growth is longer than that of most other crops.

_Rate of Application._

As to the rate per acre at which the slag ought to be applied, there
will naturally be a difference of opinion. Professor Wrightson, of
Downton Agricultural College, recommends that it should be applied at
the rate of from 6 to 10 cwt. per acre. This, of course, is very
liberal manuring. We must remember, however, that phosphatic manures,
unlike nitrogenous manures, and to some extent potash manures, may be
applied in even excessive quantities without any risk of loss. It is
impossible to measure out our phosphate manures in the same accurate
manner as we measure out our nitrogen. It is safer, therefore, and on
that account more economical in the long-run, to apply our phosphate in
excessive quantity than the reverse. The reason of this may be shortly
explained. The phosphoric acid which is naturally present in most soils
is with difficulty soluble. Only a small quantity is yielded daily to
the plant. This quantity may, under favourable climatic conditions, be
sufficient; but these favourable influences never last