ammonia salts,
our knowledge of the fact that ammonia is retained by the
soil-particles, and that before it becomes available for the plant's
needs it has to undergo the process of nitrification, teaches us the
desirability of applying it a short time before it is likely to be used.
While, lastly, with regard to the nitrogen in the various organic forms
in which it occurs, our knowledge of the rate at which these are
converted into an available form in the soil will determine when they
are best applied. Some forms of organic nitrogen are in a soluble
condition, and are quite as speedy in their action as sulphate of
ammonia. This is the case with a considerable proportion of the
different organic forms of nitrogen present in guano. Other forms of
organic nitrogen are only slightly less so--as, for example, dried
blood, which ferments very speedily. With regard, therefore, to nitrates
and ammonia salts, as well as the more quickly available organic forms
of nitrogen, they should either be applied as a top-dressing after the
plant has started growth, or only shortly before seed-time. Bones,
shoddy, and the various so-called native guanos, should be applied a
considerable period before they are likely to be required--not later
than the previous autumn.

_Phosphatic Manures._

With regard to phosphatic manures the same considerations hold good.
Inasmuch as phosphoric acid, whether applied in the soluble condition,
as in superphosphate, or the insoluble form, as in bones, basic slag,
&c., is not liable to be washed out of the soil, the risk of loss is
very slight, and need not be taken into account. As we have pointed out
in considering the action of superphosphate, phosphoric acid in this
latter form is more speedily available to the crop, and the necessity of
applying it much before it is likely to be used does not exist. Hence
superphosphate and manures which contain any appreciable amount of
soluble phosphoric acid, such as guano, should only be applied shortly
before seed-time. Bones, basic slag, or mineral phosphate ought to be
applied, on the other hand, a long time before they are likely to be
used. Hence an autumn application is to be recommended in the case of
such manures.

_Potash Manures._

Lastly, with regard to potash manures, as these are soluble, there is no
necessity for applying them much before they are likely to be absorbed
by the plant. Some are of the opinion that potash is, except in the case