e with the soil-particles.

Against, however, these undoubted advantages, one serious disadvantage
may be urged--viz., that the manure, before being ploughed in, becomes
robbed to a large extent of its soluble nitrogenous compounds, which, as
we have repeatedly observed, are so necessary for fermentation; and
that, therefore, when it is ploughed in, it does not so readily ferment.
This being so, it is highly advisable, in the case of light or sandy
soils, not to follow such a practice, but to plough the manure directly
in.

As to the depth to which it is advisable to plough the manure in, it may
be here noticed that it should not be too deep, so as to permit of the
access of sufficient moisture to ensure proper fermentation, and to
prevent rapid washing down of nitrates to the drains. Lastly, it need
scarcely be pointed out that it is highly important to have the manure
evenly and thoroughly incorporated with the soil-particles. Where the
manure is permitted to cake together in lumps, it may successfully
resist the action of fermentation for several years.

_Value and Function of Farmyard Manure._

Practical experience has long demonstrated the fact that farmyard manure
is, taking it all round, the most valuable, and admits of the most
universal application, of all manures; and science has done much to
explain the reason of this. The influence of farmyard manure is so
many-sided that it is difficult even to enumerate its different
functions. As has already been pointed out, its indirect value as a
manure is probably as great as, if indeed even not greater than, its
direct value. In concluding our study of farmyard manure, we shall
endeavour to summarise, in as brief a manner as possible, its chief
properties.

First, as to its value as a supplier of the necessary elements of
plant-food. This, there can be little doubt, has been, and still is,
grossly exaggerated by the ordinary farmer. Much has been claimed for it
as a "general" manure. How far it merits pre-eminence on this score
among other manures will be seen in the sequel. It is true that, since
it is composed of vegetable matter, it contains all the necessary plant
ingredients.[172] As has been shown in the Introduction, there is
practically in the case of most soils no necessity to add to a manure
any more than the three ingredients, _nitrogen_, _phosphoric acid_, and
_potash_. Its value, then, as a direct manure, must depend on the
quantity and proportio