3O SOILS AND FERTILIZERS 



water is of service to growing crops when it is at such 

 a depth that it can be brought to the plant roots by 

 capillarity, but when too near the surface, so that the 

 roots are immersed, the conditions are unfavorable for 

 crop growth. When the bottom water can be brought 

 within reach of the roots by capillarity, a crop has an 

 almost inexhaustible supply. In many soils known as 

 old lake bottoms, such a condition exists. 



20. Capillary Water. The water held in the minute 

 spaces above the bottom water is known as the capillary 



water. The capillary spaces 

 of the soil are the small spaces 

 between the soil particles in 

 which water is held by surface 

 tension, the force acting be- 

 tween the soil and the water 

 FIG. 12. Water Film surrounding being greater than the force 



Soil Particles. of grav i ty . Jf a ser i es Q f g j ass 



tubes of different diameters be placed in water, it will be 

 observed that in the smaller tubes water rises much 

 higher than in the larger. The water rises in all of 

 the tubes until a point is reached where the force of 

 gravity is equal to the force of surface tension. In 

 the smaller tubes surface tension is greater than the 

 force of gravity, and the water is drawn up into the 

 tube inversely proportional to its diameter. In the 

 larger tubes the surface tension is less and the water 

 is raised only a short distance. There are present in the 



