THE CONTROL OF SOIL-MOISTURE 



209 



is reached, however, the drainage should be as rapid and com- 

 plete as possible in order to insure good sanitation. The main- 

 tenance of a high absorptive capacity for available water and 

 the facilitation of rapid drainage are the secrets of rational 

 percolation control. 



Fig. 37. — ^Influence of drainage on tlie ground water and the extent of 

 the root zone. 



In this connection it is well to remember that drainage losses 

 are profoundly affected by cropping. The following data from 

 the Cornell Experiment Station are especially interesting in 

 this regard. The data for the Dunkirk and Volusia soils are 

 for ten and fifteen years respectively: 



Table XL 



AVERAGE ANNUAL LOSS OP WATER BY PERCOLATION FROM BARE 

 AND CROPPED SOILS. CORNELL LYSIMETER TANKS. 



