THE PRINCIPLES OF SOIL 

 MANAGEMENT 



A. THE SOIL AS A MEDIUM FOR ROOT 

 DEVELOPMENT 



The soil is a medium for the development of plants. 

 In the main, the plants which are of agricultural impor- 

 tance are differentiated into root and top, and the 

 former penetrates the soil in order to obtain food and 

 moisture, and to afford a firm support for the aerial 

 portion. Every plant has definite requirements for 

 its best development. The character of the mature 

 plant is the result of two sets of forces. The first of 

 these is the inherent capacity of the seed to develop 

 and produce a normal individual of its kind. The second 

 set of forces constitute the environment in which the 

 plant grows, and of which the soil is one part, the other 

 component being climate. Every plant is an expression 

 of the combination and interaction of these three 

 groups of forces the seed, the climate, and the soil. 



The external factors in plant growth may be further 

 differentiated into the following: (1) Food, (2) moisture, 

 (3) heat, (4) light, (5) air, (6) mechanical support, 

 and (7) freedom from biological enemies, such as fungous 

 disease and animal attack. With the exception of light, 

 every one of these factors is partially or wholly deter- 



A (1) 



