120 Irrigation and Drainage 



it is plain that the question, What are the largest 

 possible yields which may be realized without irri- 

 gation ? is of much greater practical moment than its 

 converse. 



THE MOST WHICH MAY BE HOPED FOR TILLAGE 

 IN THE USE OP WATER 



We have, as yet, been unable experimentally to 

 demonstrate that any method of handling the soil 

 under field conditions will permit it to abstract from 

 the air above it an amount of moisture sufficiently 

 large to materially contribute to the supply already in 

 the soil, and thus aid in compensating for a deficient 

 rainfall. The discussion presented on a preceding 

 page, regarding the production of wheat in California 

 and Washington without irrigation, certainly lends no 

 weight to the view that the hygroscopic power of soils 

 aids in supplying moisture to the crops under field 

 conditions. Still, it must be admitted that those who 

 maintain that soils do absorb important quantities of 

 moisture from the air direct may continue to do so 

 without fear of successful refutation by existing posi- 

 tive knowledge. 



If it is true that soils do not withdraw from the 

 air important quantities of water, then the most which 

 can be hoped for by methods of tillage is that they 

 may store in the soil and retain there the water which 

 falls as rain, until that shall be removed by the action 

 of the roots of the crop growing upon the field. Cer- 

 tain it is that no method of tillage now practiced can 



