104 



DRY-FARMING 



Gravitational imter 



It often happens that a portion of the water in 

 the soil is under the immediate influence of gravita- 



tiozi. For instance, a stone 



Ifl 



1 



■\vhich, normall}', is 

 covered with hygro- 

 scopic water is 

 dipped into water. 

 The hygroscopic 

 water is not thereby 

 affected, but as the 

 stone is drawn out 

 of the water a good 

 part of the water 

 runs off. This is 

 gravitational water. 

 That is, the gravita- 

 tional water of soils 

 is that portion of the 

 s i 1-w a t e r w h i c h, 

 filling the soil pores, 

 flows downward 

 t h r ugh the soil 

 under the influence 

 of gravity. AVlien 

 the soil pores are completely filled, the maximum 

 amount of gravitational wixii'V is found there. In or- 

 dinary dry-farm soils this total water capacity is be- 

 tween 35 and 40 jDer cent of the dr}' weight of soil. 



ilG. 2S. Water ino\'ing downward in 

 small tubes gradually becomes dis- 

 tributed over the waUs of the tubes as 

 a capillarj' film. 



