138 PRINCIPLES OF AGRICULTURAL CHEMISTRY 



being no distinction between subsoil and surface soil, the roots 

 thus being able to strike deep into the soil. For this reason 

 smaller quantities of water may suffice for crops. The results are 

 as follows : 



Root Area of Plants. The greater the volume of soil occupied 

 by the roots, the greater the quantity of water (and also of plant 

 food) at the disposal of the plant. Hence operations which 

 deepen the surface soil or loosen the subsoil, so as to allow the 

 roots to penetrate more deeply, have a favorable effect upon the 

 amount of water offered to the plant. The volume of soil 

 occupied by plants depends upon the nature of the plant. 



Water-Table. The water-table is the depth at which the soil is 

 saturated with water, and is indicated by the depth of the water 

 surface in shallow wells, which is slightly below the water-table. 

 The water in the water-table is termed ground water. All perman- 

 ent lakes and ponds may be considered as extension of the water- 

 table above the surface of the land. The surface of the water- 

 table follows, in a general way, the contour of the land, standing 

 highest where the ground is highest, and low where the land is 

 low. Land at the foot of hilly ground may receive a continuous 

 supply of underground water, even in time of drought. 



If a bed of impervious clay is present in the subsoil, the under- 

 ground water accumulates on its surface. The water level may 

 generally be lowered by drainage ditches or tile drains. 



The height of the water-table depends upon the character of 

 the soil, the rainfall, and the climate. It usually fluctuates, 

 rising during wet seasons and sinking during a drought. \Yhen 

 the height of the saturated layer reaches a certain point, discharge 

 takes place in the form of springs or as general drainage. 



