COMPOSTS.
The use of composts is an old one. Before artificial manures were so
plentiful as they are at present, much attention was paid by farmers to
their preparation. A compost is generally made by mixing some substance
of animal origin which is rich in manurial ingredients with peat or
loam, and often along with lime, alkali salts, common salt, and indeed
any sort of refuse which may be regarded as possessing a manurial value.
Composting, in short, may be looked upon as a useful method of turning
to profitable use refuse of various kinds which accumulate on the farm.
The object of composting is to promote fermentation of the materials
forming the compost, and to convert the manurial ingredients they
contain into an available condition for plant needs. Composts often
serve a useful purpose in retaining valuable volatile manurial
ingredients, such as ammonia, formed in easily fermentable substances
like urine. In fact, we may say that farmyard manure is the typical
compost, and its manufacture serves to illustrate the principles of
composting.
_Farmyard Manure a typical Compost._
Farmyard manure as ordinarily made is not generally regarded as a
compost, but in the past it has been widely used for the purpose of
making composts. Thus the practice of mixing farmyard manure with large
quantities of peat has been in some parts of the world a common one.
Peat, as has already been pointed out in a previous chapter, is
comparatively rich in nitrogen. When it is mixed with urine or some
other putrescible substance, the peat undergoes fermentation, with the
result that its nitrogen is to a greater or less extent converted into
ammonia. The effect, therefore, of mixing peat with farmyard manure is
beneficial to both substances mixed: the escape of ammonia is rendered
impossible by the fixing properties of the peat, while the inert
nitrogen of the peat is largely converted by fermentation into an
available form. The proportion of peat which it is advisable to add in
composting farmyard manure will depend on the richness of the quality of
the manure: the richer the quality of the manure, the greater the amount
of peat it will be able to ferment. Composts of this kind are generally
made by piling up the manure in heaps, consisting of alternate layers of
peat and farmyard manure. From one to five parts of peat to every one
part of farmyard manure is a common proportion. The use of such a
manure, containing so much organic matter, will exercise its best effect
on light sandy soils.
_Other Composts._
But instead of farmyard manure, or in addition to farmyard manure,
various other substances may be added, as bones, flesh, fish-scrap, and
the offal of slaughter-houses. Sometimes leaves and the dried
bracken-fern are used for the manufacture of composts. Some of these
substances contain much nitrogen or phosphoric acid, but in their
natural condition ferment when applied to the soil at a slow rate. If
mixed together before application in pits with peat, leaves,
bracken-fern, or some other absorbent material, fermentation proceeds
evenly and rapidly. The addition of lime, potash, and soda salts has
been found to have a most beneficial effect in promoting fermentation.
These substances, as is well known, hasten putrefaction of organic
matter. Lime seems especially to be valuable in composting. This is no
doubt due to the fact that lime plays a valuable part in promoting the
action of various ferments, as has already been illustrated in the case
of nitrification. The effect of large quantities of sour organic acids
(humic and ulmic), which are the invariable products of the
decomposition of organic matter like peat, leaves, &c., is inimical to
micro-organic life. The action of lime is to neutralise these acids.
There can be no doubt that composting is a useful process for increasing
the fertilising properties of different more or less inert manurial
substances. But in view of the abundant supply of concentrated
fertilisers, the use of composts may considerably decrease in future.