IRRIGATION OF FIELD CROPS. 213 



Stream edge will hold it against the down-stream press- 

 ure. Some use two of these canvas dams alternately 

 for each ditch that may be running, and an adlive man 

 with a sufficient head of water can run three ditches 

 abreast, while others are using only one for each ditch, 

 as the check can be put into a running ditch by cut- 

 ting the bank, placing the pole between the cut and 

 stepping with the edge of the canvas up-stream, hold- 

 ing it there until some dirt can be shoveled on the 

 lower edge in the water. It might be said that such 

 ditches as we use in wheat- fields of fair or usual fall 

 will run about a cubic foot a second, or, in other 

 words, full water rights for 160 acres will supply 

 three ditches which will water six acres. This will be 

 about eleven inches deep. This is more depth than is 

 usually needed for one irrigation. 



If the land is plowed deep, say ten inches, the land 

 cannot be covered evenly with less head. It will take 

 at least six inches to wet the top soil, as it has first to 

 be wet in order to have the water flow over it readily. 

 When water is put on a loose, dry surface it creates a 

 wet mush, and the water will immediately penetrate as 

 deep as the soil is loose. Such soil will contain a 

 much greater per cent, of water than a compa(5l, moist- 

 ened subsoil. Assuming that the water is allowed 

 to run for two hours, as it ought to to reach any 

 considerable distance from the dam on comparatively 

 level land, and all the time it is settling into the sub- 

 soil, which we will say is to the depth of two feet, this 

 soil will take another six inches of water, making 

 about a foot in all to wet the land three feet. All this 

 will be supersaturated, and in a few days it will reach 



