218 TRANSACTIONS OF THE ROYAL CANADIAN INSTITUTE.  [VOL. XI 
stand facile princeps. They constitute the basis of fertility for soils under 
cultivation; they are at once the most effective fertilizers and best ‘‘soil 
improvers’’ known. 
The function of manure in the soil may be said to be threefold: the 
supplying of the three essential elements of plant food, nitrogen, phos- 
phoric acid and potash: the inoculation of the soil with micro-organisms, 
bacteria, which give “‘life’’ to the soil and which prepare crop food 
from the store in the soil and are more especially useful in the develop- 
ment of the nitrates, the chief form of nitrogenous food for all crops 
other than the legumes; and lastly the physical improvement of the 
soil, making it mellower, warmer, better aerated and increasing its 
water-holding capacity. 
Mixed manures, that is the excreta plus the litter, of average quality 
will contain approximately per ton, 10 lbs. of nitrogen, 5 lbs. phosphoric 
acid and 1olbs. of potash, and such manure would be worth to-day for 
its plant food about $2.50 per ton. But from what has been said as to 
the several functions of manure we must ascribe to it a greater value 
than that calculated from its plant food content. The chief reason for 
this lies in the fact that it furnishes a large amount of humus-forming 
material. Humus is a very important constituent of soils, not merely 
because of its physical effect in mellowing soils and its large moisture- 
holding capacity, but because it is the natural storehouse of nitrogen, 
the most costly of all plant food elements; and because it furnishes the 
food upon which the soil bacteria thrive and develop. The colloidal 
properties of humus in holding mineral plant food that would otherwise 
be leached away to depths below the root system is also an important 
and valuable function. 
Our virgin soils of extraordinary richness and fertility, as found for 
instance in the prairie provinces, are well supplied with this humus- 
forming material; soils exhausted by cropping and irrational methods of 
farming have been depleted of this material and herein lies their poverty, 
their low productiveness, for as the humus is ‘“‘burnt”’ out, so the nitrogen 
of which it was the storehouse is dissipated. The humus content, we 
may therefore conclude, is a fair measure of the nitrogen content and of 
a soil’s productiveness. Light soils lose their humus and nitrogen more 
quickly than strong heavy loans and therefore require more frequent 
replenishment with manure or other humus furnishing material to 
maintain their fertility. If time permitted we might well dwell at 
greater length on the functions of humus, so important is its réle in © 
maintaining soil fertility. Our campaign has endeavoured to emphasize 
the necessity of keeping the soil constantly and well supplied with this 
natural builder of soils. 
