IRRIGATION 



265 



usually under pressure. It has been found advisable in 

 constructing drains for irrigated lands to sink small wells 

 into the water-bearing strata which will allow the water to 

 rise and flow away through the drain. 



Application of water. The conditions under which irri- 

 gation is practiced vary so much with soil, climate, and crops 

 that it is out of the question to give any definite rules in 

 regard to the time of application or quantity of water to 

 apply. Many of these things must be learned by experience 

 under conditions existing in any locality. The water should 

 be applied to the plant before it actually begins to suffer. 



Fig. 



221. 



After U. S. Reclamation Service 



Diversion Dam on the Yakima Project, W ashington 



In the humid states where the spray system is used yi inch 

 is considered ample for seed beds and from y£ to 1 inch for 

 a fruiting crop. Six acre-inches a season is considered the 

 maximum. In arid regions where surface irrigation is used 

 field crops require from 2 to 5 acre-feet. The best method 



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