116 Irrigation and Drainage 



underflow which gives rise to a natural sub -irrigation, it is evi- 

 dent that on such lands a much smaller rainfall, and even longer 

 intervals between rains, may occur without producing suffering 

 from drought. 



From what has been shown regarding the amount of water 

 used by different crops in coming to maturity, it is plain that 

 with a full command of water for irrigation, it would be possible 

 for crops to be grown on a given soil in a given locality when the 

 natural rainfall would not permit that crop to be so grown. It 

 is plain, therefore, that neither the amount of rain nor the dis- 

 tribution of it are sufficient to determine under what conditions 

 irrigation will or will not pay. 



