24 Transactions of the Canadian Institute. [vol. x 



ning to be realised by our farmers, indeed by agricultural chemists — 

 and we might very easily devote a whole evening to their consideration. 

 But time now forbids. As an outcome, however, of this investigatory 

 work is one fact that must not lightly be passed over. It is that the 

 percentage of nitrogen, under ordinary circumstances, is a direct index 

 of a soil's fertility, that nitrogen is the most important, the dominant, 

 the limiting factor determining crop production. In a very real sense it 

 is true that a soil's fertility may be measured by its richness in nitrogen. 

 In saying this I do not wish to be understood as minimising the import- 

 ance of the other elements of plant food furnished by the soil, but rather 

 as emphasising the unique place which soil nitrogen holds and the neces- 

 sity for its up-keep. And we have also in this connection the comforting 

 fact that in rational, economic methods of enriching a soil in nitrogen we 

 have the opportunity, constantly as it were, of keeping up a goodly supply 

 of available phosphoric acid, potash and lime, and in preserving a favour- 

 able physical condition of the soil. 



We must now pass on to consider briefly the methods that lead to 

 the destruction of the humus and the dissipation of nitrogen, and on the 

 other hand the means to be employed for the up-keep and increase of 

 these constituents. 



Their depletion, for instance, follows inevitably the practice of con- 

 tinuous grain growing, as commonly found, for example, to-day in the 

 North-West, interspersed as it is with occasional summer fallowing for the 

 purpose of conserving moisture and the eradication of weeds. Under 

 such a system an investigation carried on at one of our Western Prairie 

 Farms showed that in 22 years the soil lost to a depth of 8 inches more 

 than 2,000 lbs. of nitrogen per acre, of which approximately 700 lbs. had 

 been removed in the crops and the balance, 1,300 lbs., had been dissi- 

 pated by the constant cultivation of the soil without any addition of 

 humus-forming material. This soil is still an exceedingly rich one, and 

 capable yet for many years of bearing maximum crops in favourable 

 seasons, but chemistry tells the tale of impoverishment, and says that 

 other methods must be adopted if the land is to be maintained in its high 

 state of fertility. 



We have areas in certain districts of the Maritime Provinces and 

 Quebec once tilled and cropped, but now abandoned since they can no 

 longer be profitably farmed. All taken, nothing put back. Their humus 

 and nitrogen content have been largely dissipated, and this is undoubtedly 

 the chief cause of their present unproductiveness. Ex nihilo nihil fit. 

 Nature, in her slow but sure methods, is again restoring these worn-out, 

 abandoned lands by covering them with vegetation, but soil building by 



