they are sometimes composted with lime
and earth, or mixed with farm-yard manure, and occasionally, also, they
are used as a top-dressing to grass land.

On some parts of the western coast of Scotland and in the Hebrides,
sea-weed is the chief manure. It gives excellent crops of potatoes, but
they are said to be of inferior quality, unless marl or shell-sand is
employed at the same time.

_Leaves_ may be used as a manure, simply by ploughing them in, by
composting them with lime, or by adding them to the manure heap.

_Peat._--As a source of organic matter, peat may be used with advantage,
especially on soils in which it is naturally deficient. Dry peat of good
quality contains about one per cent of nitrogen, and a quantity of ash
varying from five to twenty per cent. These substances, however, become
available very slowly, owing to the tardy decay of peat in its natural
state; and in order to make it useful, it is necessary to compost it
with lime, or to mix it with farm-yard manure, or some readily
putrescible substance, so that its decomposition may be accelerated. It
may be most advantageously used as an absorbent of liquid manure, and on
this account, forms a useful addition to the manure heap.

The observations which have been made regarding the use of these
substances, lead directly to the inference that all vegetable matters
possess a certain manurial value, and that they ought to be carefully
collected and preserved. In fact, the careful farmer adds everything of
the sort to his manure heap, where, by undergoing fermentation along
with the manure, their nitrogen becomes immediately available to the
plant; while the seeds of weeds are destroyed during the fermentation,
and the risk of the land being rendered dirty by their springing up when
the manure comes to be used is prevented.

FOOTNOTES:

[Footnote M: The presence of sulphuret of sodium in this case is due to
the difficulty of completely burning the ash. It exists in the plant as
sulphate of soda.]

CHAPTER X.

COMPOSITION AND PROPERTIES OF ANIMAL MANURES.

Manures of animal origin are generally characterized by the large
quantity of nitrogen they contain, which causes them to undergo
decomposition with great rapidity, and to yield the greater part of
their valuable matters to the crop to which they are applied.

_Guano._--By far the most important animal manure is guano, which is
composed of the solid excrements of carnivorous birds i