CAPILLARY WATER 



gravity, and the water is drawn np into the tube. In 

 the larger tubes the surface-tension is less and water 

 is raised only a short distance. There are present in 

 the soil many spaces which are capable of taking 

 up water in the same way as the small glass tubes. 

 The height to which- water can be raised by capillarity 

 depends upon the size and arrangement of the soil 

 particles. Water may be raised by capillarity to a 

 height of several feet. Ordinarily, however, the capil- 

 lary action of water is confined to a few feet. The 



Fig. 12. Comparative height to which water rises in glass tubes. 



arrangement of the soil particles influences greatly the 

 capillary power of the soil. Usually from 30 to 60 per 

 cent, of the bulk of a soil is air space ; by compacting, 

 the air spaces are decreased ; by stirring, the air spaces 

 are increased. In soils of a close texture, as heavy 

 clays, an increase in air spaces results in an increase of 

 capillary spaces and of water-holding capacity, while 

 in other soils, as coarse sandy soils, increasing the air 

 spaces decreases the capillary spaces and the water- 

 holding capacity. The best conditions for crop pro- 

 duction exist when the soil contains water to the extent 

 of about 40 per cent, of its total capacity of saturation. 



