Value of Artificial Manwes. 
535 
manure (urine, &c.), when fermented or unfermented, has long 
been a subject of dispute with practical men. The superiority of 
effect in one case or the other is probably more due to incidental 
causes than to the actual condition of the nitrogen, but we have 
no means of proving that such is the case. The alkali potash is 
a necessary element of vegetation, but it is contained in conside- 
rable quantity in most soils, and in the ordinary course of agri- 
cultural operations is more or less restored in the farm manure. 
There is no veiy satisfactory evidence of its value as a direct 
application to the soil, or, at all events, of the exact amount of 
that value. Instances of this kind might easily be multiplied, 
but it is obvious that our power to value manures is greatly 
crippled by the insufficiency of our present knowledge of their 
effects. 
2. " Where the general value is ascertained, the same substance 
is of different value in different soils, and especially under the 
influence of variation of climates." In proof of this assertion it 
is sufficient to point to the well-known fact that bones, which 
require the influence of the air to bring them into operation, have 
altogether failed in heavy soils, where a ready-formed source of 
ammonia, such as guano, has produced the best effect. 
Again, certain soils contain a superabundance of particular 
ingredients of manure ; the use of it then becomes unnecessary, 
and its cost in a manure is not compensated by any advantage 
from its application. Some of the surface soils of the greensand, 
as at Farnham, contain large quantities of phosphate of lime, 
and it results from the experience of Mr. Paine, whose land is so 
situated, that the direct application of phosphate of lime to such 
land is useless. In buying a manure, therefore, he could not 
afford to pay for this ingredient. Difference of climate is perhaps 
even more than variety of soil productive of modification in the 
action of manures. In the North guano is extensively used for 
turnips ; in the South of England its employment for this crop is 
comparatively limited. 
3. " The value is not the same for all crops." It seems to 
be proved beyond all doubt by the experiments of Mr. Lavves 
and Dr. Gilbert that ammonia is the manure for direct applica- 
tion to the cereals ; phosphate of lime being properly applied 
to turnips and other root-crops, but being quite without effect 
upon wheat.* 
Now, although a certain quantity of ammonia in a turnip-manure 
may not only be allowable but desirable, and possibly, on the other 
hand, a small portion of phosphate of lime may improve a corn- 
* The more recent experiments of these gentlemen on barley and oats induce 
them to believe that soluble phosphate of lime has in some cases a beneficial action 
on these crops. 
