6 Irrigation and Drainage 



In passing south from San Francisco, through Lath- 

 rop, Merced and Fresno, to Bakersfield, in California, 

 we pass across a long stretch of country where there 

 is at present relatively very little irrigation, and yet 

 through all of the country north of Merced wheat has 

 been extensively grown, and during the early years, 

 when the soil was new, large yields per acre have been 

 realized without irrigation, the crop depending upon 

 the rain which falls during the rainy season of winter 

 and sinks into the soil, to be later used by the deeper 

 feeding roots. In discussing the matter with Professor 

 Hilgard, he informed me that the roots of crops 

 penetrate these soils much more deeply than is normal 

 to them under other conditions, and that some plants, 

 when brought here, really change their habits of root 

 growth through a dying off of the normal surface 

 feeders on account of an insufficiency of moisture in 

 the upper layers. 



Professor Hilgard further informed me that over 

 much of the state of California the rains only wet 

 down a relatively short distance, and that beneath this 

 zone of moistened soil the balance is often almost 

 air -dry, extending, in certain cases which have come 

 under his observation, to depths as great as forty feet. 

 Where such conditions as these exist there is, of 

 course, no possibility of crops deriving a supply of 

 moisture through natural sub - irrigation from waters 

 from the foothills or higher mountain masses which 

 rise above the plains. 



My own observations on the soils of humid cli- 

 mates convince me that the zone of dry soil to which 



