apt to encourage rankness of
growth--an undue development of straw at the expense of the grain. It is
consequently customary to apply farmyard manure to the preceding crop.
The direct application of farmyard manure to wheat, however, according
to Sir J. B. Lawes, is not fraught with unfavourable results where the
soil is a light one; it is only when the soil is of a heavy nature that
it is best to apply it to the preceding crop. Potatoes are another crop
to which it is best not to apply it directly. On the other hand, many
are of the opinion that mangels seem to be able to benefit from large
applications of farmyard manure.

_Conditions determining the Application of Artificial Manures._

In the application of artificial manures a large number of
considerations have to be taken into account. Among these may be
mentioned the nature of the manure itself, and its mechanical and
chemical condition; the nature of the soil and its previous treatment
with manures, as well as the nature of the climate, the nature of the
crop, and the previous cropping. It may be well, therefore, to examine
somewhat in detail some of these considerations.

_Nature of the Manure._

Nitrogen, phosphoric acid, and potash exist in the common manures, as
has already been pointed out, in different states of availability.
Nitrogen, for example, may exist in a soluble or insoluble condition, as
nitrates, as ammonia, or in various organic forms. Phosphoric acid,
similarly, may exist in a soluble form, as it does in superphosphate of
lime, or in an insoluble form, as it does in bones or basic slag.
Potash, on the other hand, exists--or should exist--in artificial
manures only in a soluble form. Now a correct knowledge of the behaviour
of these different forms of the common manurial ingredients when applied
to the soil is, in the first place, necessary for their successful and
economical use.

_Nitrogenous Manures._

Thus our knowledge of the inability of the soil-particles to retain
nitrogen in the form of nitric acid, as well as our knowledge of the
fact that nitrogen is in this form immediately available for the
plant's needs, teaches us that nitrate of soda should never be applied
before the plant is ready to utilise it--in short, that it should only
be applied as a top-dressing; and further, that the use of such a
fertiliser in a damp season is less likely to be economical than in a
dry one. Again, with regard to nitrogen in the form of