THE POSSIBILITIES OF ARTIFICIAL MANURES IN FORESTRY. 255 
brought about by the addition of artificial manures in proper 
amount at the proper time and in the proper sequence. We 
must, however, remember that the action of artificial manure 
may be direct or indirect; that is, the ingredients it contains 
may be brought into solution and directly absorbed by the trees, 
or these substances may lead to double decompositions taking 
place, rendering material already present in the soil available 
for the plant. The former is the direct action, the latter the 
indirect action, of the added substance. 
As already indicated, soil analysis, or even analysis of the 
plant itself, does not give us sufficient data regarding the 
quantity and kinds of artificial manures which should be added. 
This can only be found out, in the first place, by experiment with 
the living plant itself, and the experience so gained will indicate 
the: plan to be adopted in other places with similar soils and 
climate. 
Before leaving the important subject of the preparation of food 
material in the soil, let us for a moment consider the process of 
nitrification. Among the various nitrogenous manures, the only 
one capable of being directly absorbed by the trees is nitrate 
of soda. The nitrogen contained in the other substances, 
humus, green manure and sulphate of ammonia, must first 
undergo conversion into nitrites and then into nitrates before it 
becomes generally available for absorption. These important 
changes are brought about by the vital action of organisms 
living in the soil, the so-called nitrifying bacteria. If the 
chemical and physical conditions of the soil are such that the 
healthy development of these organisms is interfered with, then 
the supply of available nitrogen in the form of nitrates is 
seriously diminished. Without going further into the subject 
here, it may be sufficient to state that artificial manures keep 
the soil in a condition favourable to these very important 
organisms. 
As regards the application and utility of the various manures, 
the following points may be of interest :— 
Nitrogenous Manures.-—Nitrate of soda is easily dissolved, and 
the solution is directly absorbed by the plant. Its effect is 
therefore very rapid, and if it is not immediately absorbed by 
the trees, there is danger of its being washed out of the soil; 
hence this salt should only be applied when the roots are in an 
actively vegetative condition, and, further, the quantity given 
