cent, containing nitrogen .4 to .65 per
cent. The total mineral matter will range from about 4 to 6.5 per cent,
containing of potash from .4 to .7 per cent, and of phosphoric acid from
.2 to .4 per cent.[165]

As Mr Warington[166] has pointed out, one ton of farmyard manure would
thus contain 9 to 15 lb. of nitrogen, about the same quantity of potash,
and 4 to 9 lb. of phosphoric acid. These quantities of nitrogen and
phosphoric acid, calculated to (95 per cent) nitrate of soda, and (97
per cent) sulphate of ammonia, and (25 per cent) superphosphate, give
respectively 57.25 to 96 lb. nitrate of soda, 45 to 75 lb. sulphate of
ammonia, and 35 to 79 lb. superphosphate. That is, in order to apply as
much nitrogen to the soil as is contained in one ton of nitrate of soda,
we should require to use from 23 to 41 tons of farmyard manure:
similarly one ton of sulphate of ammonia contains as much nitrogen as 30
to 50 tons farmyard manure. In the same way one ton of superphosphate
of lime contains as much phosphoric acid as 28 to 64 tons farmyard
manure.

The value of rotten manure is, weight for weight, greater than that of
fresh manure. This is due to the fact that, while the water increases in
amount, the loss of organic matter of a non-nitrogenous nature more than
counterbalances the increase in water. The manure, therefore, becomes
more concentrated in quality. The loss on the total weight, according to
Wolff, in the rotting of farmyard manure, should not exceed in two or
three months' time 16 to 20 per cent--viz., a sixth to a fifth of its
entire weight. Not only, however, does the manure become richer in
manurial ingredients, but the forms in which the manurial ingredients
are present in rotten manure are more valuable, as they are more
soluble. These statements must not be taken as proving that it is more
economical to apply farmyard manure in a rotten condition than in a
fresh one. The distinction must not be lost sight of which exists
between relative increase--increase in the percentage of valuable
constituents--and absolute increase. The increase in the value of the
manure by the changes of the manurial ingredients from the insoluble to
the soluble condition may be effected at the expense of a considerable
amount of absolute loss of these valuable ingredients. This is a point
which is probably too often left out of account in discussing the
relative merits of fresh and rotten farmyard manure; and it is
important that