4 Irrigation and Drainage 



Then, again, on the other hand, the soil which for 

 a given climate is so close-grained that it does not 

 drain sufficiently between rains to leave it dry enough 

 for those crops which have become accustomed to the 

 smaller water capacity of the coarser soils, may be all 

 right for the dry -soil crop, provided it occurs in a 

 locality of smaller or less frequent rainfall. Or, again, 

 in the region of heavier rainfall, this soil may be fitted 

 for the dry-soil crop by thorough under- draining, when 

 the lines of tile are placed close enough to draw down 

 the water to a sufficiently low point to leave the soil 

 with the amount of moisture which is suited to the 

 crop in question. 



Another soil may be very deep and exceptionally 

 well aerated, on account of its peculiar texture, so 

 that the roots of cultivated crops easily penetrate it to 

 much greater depths than is possible in the closer, 

 more compact, non-aerated subsoils of other localities. 

 When this is the case, as appears often to be true 

 in arid and semi -arid climates, notably in parts of 

 the San Joaquin Valley, in California, the smaller rain- 

 fall of the winter season penetrates the soil so deeply, 

 and returns to the surface by capillarity so slowly, that 

 fair and even large crops are often raised on these 

 soils without artificial irrigation, yet not a drop of 

 rain may fall upon the land from May first to Septem- 

 ber. So different are the conditions in humid soils, like 

 those of the eastern United States, that even a period 

 of ten days without rain, especially if it occurs in the 

 height of the growing season, is sure to bring marked 

 distress even to field crops like maize. 



