204 



THE PRINCIPLES OF SOIL MANAGEMENT 



lary capacity, and, further, it had a full supply of water 

 at the bottom of the column, conditions seldom found 

 in practice, and certainly not common under arid- 

 climate conditions. The curves of water loss, showing 

 the mulching effect of rapid drying, appear below: 



300 



< 200 



100 









20 



25 



6 10 15 



TIME IN DAYS 



Fig. 64. Curves showing the relative evaporation of water from two col- 

 nm-is of the same soil. One was kept in a dry atmosphere at the immediate 

 sur.'ace. The other was maintained under normal humid climate conditions of 

 moisture and temperature. 



For the reasons presented, the moisture supply in 

 arid regions appears to be naturally more effectively 

 conserved than in humid regions, certainly a wise 

 provision. This fact is to be connected with the further 

 one that capillary movement into the deep subsoil is 

 very slow. 



The mulching effect described above gives further 

 emphasis to the unwisdom of frequent small applications 

 of water to the soil. 



In humid regions the natural mulching effect is 

 much less marked than in arid regions. If the farmer 

 would produce a soil mulch, he must do it by creating 

 as far as possible the arid conditions. That is, he must 

 bring about such a rapid drying of the surface soil as 

 to convert it into a mulch which will retain the moisture 



