7O SOILS AND FERTILIZERS 



integrated minerals have been removed from rocks by 

 leaching and other agencies. It is known that the 

 rate of weathering of soils is influenced by various fac- 

 tors, as origin, texture, composition, humidity and other 

 climatic conditions, presence of decaying organic matter, 

 micro-organisms, mechanical treatment and manipula- 

 tion of the soil, fertilizers, sunlight and vegetation. 

 Some of these agencies for promoting soil disintegra- 

 tion are under the control of the farmer and are utilized 

 by him in rendering plant food available. A knowledge 

 of the origin of soils, of the minerals of which they are 

 composed, and of the ways in which they have been 

 distributed is of much assistance in determining their 

 agricultural value. 



