ound in the drainage-water.

_Amount produced at Different Times of the Year._

Some indication of the rate at which nitrification takes place during
the different months of the year is obtained from a study of the results
of the analyses of drainage-waters which we have just referred to. This,
however, it must be remembered, only furnishes us with a very
approximate indication. The month showing the greatest amount of
nitrates in the drainage-water must not necessarily be regarded as that
during which nitrification has been most active, for the amount chiefly
depends on the rainfall. In illustration of this it will be found that
the drainage-water during the autumn and early winter months contains
most nitrates, not because nitrification is most active then, but
because the rainfall is greatest, and a large proportion of the nitrates
formed during the drier summer months is being only then washed from the
soil. The amount of nitrates in drainage-waters steadily diminishes from
autumn through the winter months, and is least in spring. The total
amount of nitrates found in the drainage-water is, therefore, not a safe
guide. What, however, does furnish us with a more reliable indication is
the _percentage_ of nitrates in the drainage-water. Regarding the
results of the analyses of drainage-water (see Appendix) from this point
of view, it will be seen that this is greatest during the month of
September, and least during April.[122]

_Nitrification of Manures._

A subject which has not yet been specially referred to, but which is of
great practical importance, is the nitrification of manurial substances.
It is unfortunate that the amount of research hitherto devoted to this
important question has been slight, and that the knowledge we possess is
therefore very limited.

_Ammonia Salts most easily Nitrifiable._

One fact, however, about which there can be little doubt, is that
nitrogen in the form of ammonia salts is, of all compounds of nitrogen,
the most easily nitrifiable. Indeed, as we have already indicated, it is
highly probable that the conversion of the different forms of organic
nitrogen into ammonia is an intermediate stage in the nitrification of
these bodies. At any rate it seems to be invariably the case that when a
mixture of nitrogen compounds, including ammonia salts, are allowed to
nitrify, the nitrogen in the form of ammonia is the first to become
nitrified.

_Sulphate of Ammonia most easily