G. EXTERNAL FACTORS IN SOIL MANAGEMENT 



In the foregoing chapters, some of the principles 

 underlying the management of the soil have been 

 pointed out. In addition to these are several practices 

 associated with soil management resting upon the prin- 

 ciples that have been explained, which are so funda- 

 mentally important as to warrant their separate discus- 

 sion in this connection. 



I. MEANS OF MODIFYING THE SOIL 



In the art of soil management, one has a number 

 of practices which may be used to modify the soil. 



331. Summary of practices. The most prominent 

 of these practices are: (1) The manipulation of the soil 

 by means of implements. (2) Drainage. (3) Irrigation. 

 (4) Application of amendments, including all forms 

 of organic materials. (5) Application of chemical ma- 

 nures. (6) Inoculation. (7) Rotation. (8) Crop- 

 adaptation. 



Each of these practices has a primary function. 

 That of drainage is to remove excess water from the 

 soil; of chemical manures to add food elements; of inocu- 

 lation, to introduce organisms; of tillage, to modify 

 the structure of the soil. But, in the exercise of their 

 primary function, each practice also has many second- 

 ary or indirect effects on the soil, which may sometimes 

 be more important to the productive qualities of the 

 dd (465) 



