INTRODUCTION 



The study of the soil, which is fundamental in any 

 application of science to that part of agriculture which 

 deals with the growth of crops, has received greatly 

 increased attention during the past few years. The 

 crude chemical point of view, which in the main 

 regarded the soil as a nutritive medium for the 

 plant, has been altogether extended, by a considera- 

 tion of the soil as the seat of a number of physical 

 processes affecting the supply of heat and of air 

 and water to the plant, and again as a com- 

 plex laboratory, peopled by many types of lower 

 organisms, whose function is in some cases indis- 

 pensable, in others noxious, to the higher plants with 

 which the farmer is concerned. These three kinds of 

 reaction chemical, physical, and biological interact 

 upon one another and upon the crop in many ways ; 

 they are affected by, and serve to explain, the various 

 tillage operations which have been learnt by the 

 accumulated experience of the farming community, 

 and the hope for future progress lies in the further 

 adaptation for practical ends of these processes at 

 work in the soil. But it must not be supposed that 

 science is yet in a position to reform the procedure of 

 farming, or even to effect an immediate increase in the 

 productivity of the land : agriculture is the oldest and 

 most widespread art the world has known, the applica- 



