400 Irrigation and Drainage 



ditch, and maintenance, which, in the aggregate, 

 could not be less than $12.88 per acre when done on 

 a large scale and under the most favorable conditions, 

 or a total cost of $100 per acre, at the very best 

 figure which could be hoped for. 



Only in those cases where tile could be placed 

 barely below the surface could there be as high a 

 duty of water as with furrow irrigation, and hence, 

 where water is high and labor cheap, the cost of water 

 would decide against sub -irrigation. 



Where a field has been underdrained, as repre- 

 sented in Fig. 124, in the lower lefthand corner, it is 

 easy to introduce the irrigation water at the upper 

 end of the main, as shown at F, and allow it to set 

 back through the laterals. By forcing the water in 

 the main to rise to the surface of the ground at G, 

 H and A before passing on to lower levels, the 

 water in all the tile would be placed under pressure 

 which would force it to the top of the ground with- 

 out waiting for capillarity to bring it there. In 

 this manner if the field were underlaid by sand at the 

 level of the tile, the whole area may be quickly 

 watered, provided the main has capacity sufficient to 

 deliver the water to all the laterals as rapidly as 

 percolation can take place from them. With the 

 outlet of the tile at E closed and water admitted to 

 the main at both F and A, the 7,022 feet of tile took 

 water at the rate of 48 cubic feet per minute under 

 the 5 acres, or at the rate of 5 gallons per 100 run- 

 ning feet of tile where these were placed in sand 33 

 feet apart. During the irrigation, water was brought 



