32 SOILS AND FERTILIZERS 



29. Cultivation After a Rain. When evaporation 

 takes place immediately after a rain, not only is there 

 a loss of the water which has fallen, but there may 

 also be a loss of the subsoil water by translocation, if 

 nothing be done to prevent. 13 The following example 

 shows the extent to which, the subsoil water may be 

 brought to the surface. 14 



Per cent, of water. 



Surface soil. Subsoil. 



I to 3 inches. 6 to 12 inches. 



Before the shower 9.77 18.22 



After the shower 22.11 16.70 



The rainfall was sufficient to have raised the water 

 content of the surface soil to 20.77 per cent. The 

 subsoil showed a loss of 1.52 per cent, while the sur- 

 face soil showed a gain of 1.34 per cent, in addition to 

 the water received from the shower. If evaporation 

 begins before the equilibrium is reestablished, there is 

 lost, not only the water from the shower, but also the 

 water which has been translocated from the subsoil to 

 the surface. Hence the importance of shallow surface 

 cultivation immediately after a rain. 



When a subsoil contains a liberal supply of water, 

 and the surface soil a minimum amount, there is after 

 a shower a movement of the subsoil water to the sur- 

 face. The soil particles at the surface are surrounded 

 with films of water which thicken at the expense of 

 the subsoil water. Surface-tension is the cause of this 

 movement of the water to the surface, and under the 

 conditions stated it is temporarily greater than the 

 force of gravity. 



A hard thin crust should never be allowed to form 



