Nitrifiable Manure._

It follows from this that sulphate of ammonia, the most common of
ammoniacal manures, is one of the most speedily nitrified when applied
to the soil. The rate at which the nitrification of this manure takes
place naturally varies according to the quantity applied, and other
circumstances, such as the nature of the soil and the weather, &c. That,
under favourable circumstances, the conversion of ammonia into nitrates
is very rapid, has been shown by a number of experiments. Deherain has
found that when sulphate of ammonia was mixed with soil at the rate of 2
cwt. per acre, nitrification took place at the rate of 1/100th of its
nitrogen per day.

_Rate of Nitrification of other Manures._

Of other nitrogenous manures, guano, it would seem, comes next to
sulphate of ammonia in the rate at which it becomes nitrified in the
soil; while next to guano stand green manures, dried blood, meat-meal,
&c. As we should expect, such a manure as shoddy is very slowly
nitrified. The rate at which the nitrogen compounds in farmyard manure
become nitrified, when incorporated with the soil, vary very much
according to circumstances. It goes on probably at a greater rate than
the ordinary nitrification of soil-nitrogen. It is a somewhat striking
fact that the effect of adding nitrate of soda to the soil may be at
first to check nitrification. That the addition of common salt, even in
small quantities, has this result, is at any rate certain. The presence
of salt to the extent of one-thousandth of the weight of the soil, has a
prejudicial effect.

_Soils best suited for Nitrification._

To recapitulate, then, nitrification is effected through the agency of
micro-organisms, which are present to a greater or less extent in all
soils. It requires for its favourable development air, warmth, moisture,
absence of strong light, presence of a salifiable base--viz., carbonate
of lime--the presence of certain mineral food-constituents, such as
phosphates, and a certain amount of alkalinity. It consequently takes
place to the least extent in barren sandy soils. Soils rich, light, well
ventilated, uniformly moist, warm, and chalky, are best suited for its
development. Other things being equal, it develops better in a
fine-grained soil than in a coarse-grained soil, because, in the case of
the former, aeration and uniform moistening of the soil are best
secured.

_Absence of Nitrification in Forest-soils._

A point of co