on exists in the amount of
phosphates, and probably of their other constituents. They have all been
employed with success, but the most accurate observations have been made
with rape-dust, which has been longer and more extensively used than any
of the others. It has been employed alone for turnips, or mixed with
farm-yard manure, and also as a top-dressing to cereals. But the most
marked advantage is derived from it when applied in the latter way on
land which has been much exhausted, and its effects are then very
striking. An adequate supply of moisture is essential to the production
of its full effects, and hence it often proves a failure in very dry
seasons, and on dry soils. It must not be applied in too great
abundance, experience having shewn that after a certain point has been
reached, an increase in the quantity produces no benefit, and even
sometimes positively diminishes the crop. The other substances of the
same class, in all probability, act in the same way, but as their
introduction is recent, and their use limited, less is known regarding
their effects.

_Malt-Dust, Bran, Chaff, etc._--The value of these substances as manures
is chiefly dependent on the nitrogen they contain, though to some extent
also on their inorganic constituents. Malt-dust contains about 4.5 per
cent, and bran 3.2 per cent of nitrogen. But they are little used as
manures, as they can generally be more advantageously employed for
feeding. The value of chaff more nearly resembles that of straw.

_Straw_ is occasionally employed as a manure, and sometimes even as a
top-dressing for grass land. It is generally admitted, however, that its
application in the dry state, and especially as a top-dressing, is a
practice not to be recommended, as it decomposes too slowly in the soil;
and it is always desirable to ferment it in the manure heap, so as to
facilitate the production of ammonia from its nitrogen. Still
circumstances may occur in which it becomes necessary to employ it in
the dry state, and it will generally prove most valuable on heavy soils,
which it serves to keep open, and so promotes the access of air, and
enables it to act on the soil. On light sandy soils it generally proves
less advantageous, as its tendency of course is to increase the openness
of the soil, and render it less able to retain the essential
constituents of the plant.

The quantity of nitrogen in straw does not exceed 0.2 per cent, and its
value is mainly due