CULTIVATION. 75 



CHAPTER III. 

 CULTIVATION. 



IN the last chapter the soil was considered from the point 

 of view of its relation to the life of the plant; here it will be 

 treated of in its relation to cultivation and the production 

 of crops. To begin with, it is necessary to distinguish 

 between the part of the soil which is ploughed or other- 

 wise tilled and the part lying below, beyond the reach 

 of ordinary tillage operations. The upper part which 

 is ploughed is called the "soil" and the part below, the 

 "subsoil.'' The surface of the subsoil on which the sole 

 of the plough runs when tilling the soil is usually much 

 compressed and is called the "plough-pad." The depth 

 of the soil is between 16 and 20 cms., varying with the 

 depth of tillage ; the subsoil is usually much deeper 

 than is required for plant growth. In Egypt the soil 

 and subsoil are very similar in character, nevertheless 

 there must be some difference, otherwise the continual 

 cultivation of the surface has no effect. The mineral 

 particles of which the soil and subsoil are composed are 

 seldom of exactly the same character. Thus the soils 

 and subsoils of samples 2 and 3, of the last chapter (p. 38) 

 show marked differences. Even when the mineral particles 

 are exactly the same, the soil is richer in available plant 

 food than the subsoil for the following reasons : 



1. The soil has not been so long deposited, it has not 

 borne so many crops and is therefore in a less exhausted 

 condition than the subsoil. 



