THE CONTROL OF SOIL MOISTURE 287 



because a greater amount of surface is exposed over 

 which evaporation may take place. On the other hand, 

 wide experience, as well as investigation, indicates that, 

 for the conservation of water, level culture is better than 

 ridged culture. This principle has led to the gradual 

 abandonment of the practice of " laying by " corn and 

 potatoes with a high ridge. In all regions of deficient 

 rainfall, the best practice prescribes level tillage and a 

 fine, dry mulch, both of which are attained by the frequent 

 use of shallow-running small-tooth cultivators. Many 

 experiments have demonstrated the larger crop yields 

 to be obtained, on the average, from this practice. 



205. Plants. — Plants growing on the soil tend to 

 check evaporation from two causes — (1) their shading 

 effects, and (2) the tendency of the roots to intercept 

 capillary water as it moves upward and to appropriate 

 it for plant growth. Plants, however, tend to intercept 

 a certain amount of rain and prevent its ever reaching 

 the soil. The amount of water wasted in this way by 

 forests ranges from 15 to 30 per cent. In general this 

 tendency just about offsets the saving that occurs from 

 shading. 



206. Summary of moisture control. — It is clearly seen 

 from the discussion of moisture control that the structural 

 condition of the soil is the secret of successful operation. 

 Run-off and leaching are reduced by increased capillary 

 capacity, a structural relationship. Evaporation is 

 checked by a soil mulch, which depends for its effective- 

 ness on its physical condition. Drainage, lime, addition 

 of organic matter, and tillage in perfecting granulation 

 function in increasing the ease and effectiveness with 

 which soil moisture may be controlled. It must be 

 clearly kept in mind that all such control is directed 



