IRRIGATION IN HUMID CLIMATES 413 



tions. There should be no differentiation in the irrigation 

 practices of humid and arid regions. In both regions there 

 should be an adaptation of the general principles to the 

 special needs of the community. 



245. The duty of water. Since irrigation is merely 

 supplementary to the rainfall, less irrigation water is ordi- 

 narily required in humid regions than in arid regions. 

 One to 3 inches of water applied at each irrigation is 

 common under humid conditions, and is apparently 

 abundant. In arid regions, on the other hand, 3 to 5 

 inches, or even more, are applied at each irrigation. In 

 the humid regions, plants are likely to be somewhat 

 shallow-rooted, owing to the abundance of moisture in the 

 early growing season. This makes it unnecessary for the 

 roots to move deeply in the soil and therefore more 

 frequent irrigation is probably necessary than in arid 

 regions. However, the application of water every ten or 

 fifteen days should be sufficient. In general, the duty of 

 water in humid regions should be higher than in arid 

 regions, but this does not always follow, for it is reported 

 that to irrigate sugar cane, under humid conditions, a 

 depth of water equivalent to 40 to 100 inches is used 

 throughout the season, which is much more than is neces- 

 sary in the arid regions. It is probable that, in humid as 

 in arid regions, the tendency will be to use too much 

 water. Over-irrigation is just as objectionable in humid 

 as in arid climates, and for the reasons already stated 

 in previous chapters. 



246. Sources of water. The humid region abounds 

 in creeks, ponds, rivers and underground water, all of 

 which are suitable for irrigation. However, water-rights 

 in the East, where irrigation has received little attention, 

 are more complicated, and frequently it is more difficult 



