INTRODUCTION 3 



No soil is perfect ; no soil quite hopeless ; much can be 

 done to improve the bad, and much can be left undone to 

 injure the good. Those soils which have grown grass or 

 timber for many years have a great accumulated fertility 

 and need but little, if any, fertilizer, though it is not 

 infrequently the case that such '* virgin " soils are not as 

 rich as reported. In Canada, for example, the prairie soils 

 grow as good crops of wheat as do the highly farmed fields 

 of England, but elsewhere most of the soils treated as if they 

 were fertile virgin soils produce relatively low wheat yields. 

 Soils that appear naturally barren are often deficient 

 in water supply, although excess of water is also a cause of 

 sterility. A class of soil very common in old farmed districts 

 is the exhausted soil. Wheat can be grown for many years 

 in succession on the same land with a minimum amount of 

 manure, but the yield per acre gradually falls. Other crops 

 reach a state of exhaustion at a much greater rate, although 

 it has been found in many cases that the returns can be 

 maintained by appropriate treatment and by application of 

 the right fertilizers. 



From the point of view of the Industrial Chemist, the 

 fertilizers are by-products of industry which proceed to agri- 

 culture only to reappear in new forms of plant products, 

 to again form part in some industrial enterprise. It is there- 

 fore convenient in this volume of the series to begin with a 

 discussion of the fertilizers. These form a group of bodies 

 whose values and classifications depend on the uses to which 

 they are put rather than upon their origins, 

 ^^t For the purpose of studying the fertilizers it is necessary 

 ^^fto consider more than one system of classification. 

 Y^m A useful general system will be to regard the fertilizer 

 mjas a means of supplying a particular chemical element as 

 follows : — 



1. The nitrogen group. 



2. The phosphorus group. 



3. The potassium group. 

 There will be many fertilizers that fall into more than 



one such group. 



