THE ^POTATO 105 



ditches lose a great deal by seepage, and until they 

 become silted up they do not carry as much water 

 as their size would indicate. New land in an arid 

 district takes more water the first year than it 

 ever requires thereafter. For an 80-acre tract of 

 new land the supply ditch should be made with 

 a slip scraper and it should generally be at least 

 one foot deep in the solid ground, to say nothing of 

 the height of the banks made by the dirt scraped 

 out. 



"Care should be used to run the distributing 

 laterals on a light grade, because water must be 

 taken out of them for the corrugations or checks, 

 and if they have a heavy grade it is a difficult 

 thing to do, because it requires so many checks in 

 the laterals. These laterals can be made with a 

 plow and a go-devil, or a regular ditch plow. The 

 corrugations should be run in the direction of the 

 greatest fall. 



"The best method of irrigation to be followed 

 is dependent upon the character of soil and the 

 slope of the land. The corrugation system is 

 suitable for land that takes up water readily and 

 that has ten feet of uniform slope per mile (a 

 trifle more than one inch per fifty feet) or more. 

 Corrugations may be placed as close together as 

 is necessary. Usually twenty inches apart is the 

 minimum width and three feet apart the maximum. 

 The furrows are made about four inches deep and 

 should be made immediately after seeding or be- 

 fore the seed germinates. In old alfalfa fields 

 the corrugations can be renewed when it becomes 

 desirable with an iron corrugator that has sharp, 

 plow-like points. 



"Sub-laterals are made parallel with the laterals. 

 For corrugation or furrow irrigation in Idaho 



