192 



IRRIGATION PRACTICE 



ditches sinks until it reaches the clay bottom, along which 

 it travels for great distances within reach of plant roots. 

 Some of the finest fields in western America are supplied 

 with water by this inexpensive process of natural lateral 

 seepage. Clearly, this method is so limited in extent that 



mm" 



GRAVEL GRAVEL 



Fio. 33. Lee's sub-irrigation system. 



it deserves only a passing notice. Yet it should be kept in 

 mind, so that, whenever the conditions appear to be 

 suitable, attempts may be made to irrigate crops by 

 natural sub-irrigation. (Figs. 32, 33.) 



Except in greenhouses and under natural systems, sub- 

 irrigation may be eliminated from consideration. 



