n in which these three ingredients are present.
These substances, as we have already seen, it contains only in very
small quantities. It is, judged from this point of view, a comparatively
poor manure. Furthermore, only a certain percentage of these substances
is in a soluble or immediately available condition,--in this respect the
rotten manure being very much more valuable than the fresh manure.

Again, a point of great importance in a universal manure is the
proportion in which the necessary plant-foods are present. If it be
asked, Are the nitrogen, phosphoric acid, and potash in farmyard manure
present in the proportion in which crops require these constituents? the
answer must be in the negative. Heiden[173] has very strikingly
illustrated this point, in so far as the relations between the two ash
ingredients are concerned, by some computations as to the amount which
would be removed from the soil in the course of different
rotations.[174] In the case of five different rotations it was found
that the ratio between the potash and phosphoric acid removed was as
follows:[175] (1) 2.96 to 1; (2) 2.76 to 1; (3) 2.95 to 1; (4) 4.13 to
1; (5) 3.78 to 1. This would give a mean of 3.32 to 1. This is not the
ratio in which these ingredients are generally present in farmyard
manure. Farmyard manure may be said to be much richer in the mineral
constituents of plants than in nitrogen. Professor Heiden found that in
the case of a farm at Waldau, the crops in the course of ten years
removed from a _morgen_ (.631 of an acre) the following quantities:--

lb.
Nitrogen 329
Potash 263
Phosphoric acid 121

In order to supply these amounts the following quantities of manure
would require to be supplied:--

1. For the nitrogen, 26 or 27 tons (manure containing .606 per cent
nitrogen).

2. For the potash, 20 to 25 tons (manure containing .672 per cent
potash).

3. For the phosphoric acid, 13 to 19 tons (manure containing .315 per
cent phosphoric acid).

From the above it will be seen that farmyard manure contains too little
nitrogen in proportion to its ash ingredients.

It is not merely the amount of fertilising ingredients removed by the
crop we have to take into account in estimating the value of certain
manurial ingredients for the different crops. Two other considerations
have to be remembered--viz., the amount of the constituents already
present in the soil, and