PHYSICAL INTER-RELATIONS IN SOILS 53 



To wash from the soil objectionable salts which, if 

 allowed to accumulate, might do harm to plant life. 



Aside from the desirable functions named above, the 

 presence of gravitational water in a soil works harm 

 rather than good, and the list of resulting evils is long and 

 coextensive. The continued presence of gravitational 

 water in a soil : 



Destroys soil structure, which results in a number of 

 associated evils, and increases the labor required in 

 preparing the seed-bed, and in performing many of the 

 operations necessary in caring for and harvesting the 

 crop. 



Interferes with soil ventilation either directly by par- 

 tially or wholly occupying the pore-space of the soil, or 

 indirectly by modifying the soil structure. In either case 

 there follows a partial or complete interruption of germina- 

 tion, plant growth, and food preparation. There follows, 

 also, food removal and food destruction. 



Reduces temperature, because of the removal of heat 

 from the soil, or the diversion of heat that would other- 

 wise get to the soil. The result here is interruption or 

 prevention of (1) germination, (2) root action, (3) food 

 preparation (chemical, physical, biological). The ulti- 

 mate result is (1) increased labor, (2) increased incon- 

 venience, (3) decreased yields, and even (4) total failure of 

 crops. 



It is evident, therefore, that the presence of gravi- 

 tational water in agricultural soils, even for moderately 

 extended periods, is undesirable, and that, when neces- 

 sary, means should be provided to prevent such presence. 



