190 IRRIGATION PRACTICE 



benefit overshadows the loss by evaporation. In the 

 Utah work, some attention was given to the effect of irri- 

 gation above ground with respect to the transpiration 

 ratio. In every case, much larger quantities of water 

 were evaporated when the water was applied to the sur- 

 face of the soil than when applied by sub-irrigation, but a 

 pound of water applied to the surface produced as much 

 dry matter as when applied below the surface. It may be 

 that the value of sub-irrigation has been considerably 

 exaggerated because the diminution of evaporation only 

 has been considered. 



Aside from these theoretical considerations, sub-irri- 

 gation has not received wide acceptance, due to certain 

 intrinsic difficulties, which seem insurmountable. Sub- 

 irrigation implies underground water channels, opened 

 at various places for the escape of water to the crop. 

 These underground channels are usually pipes of iron or 

 concrete or wood. Machines are on the market which, 

 as they move along, open the soil to the requisite depth 

 and at the same time lay a concrete pipe of the desired 

 dimension. The cost of installing such a system is very 

 great and adds immensely to the initial cost of irrigation. 

 With the present prices of land, water and crops, it is not 

 good business to install sub-irrigation systems, unless it 

 be in a few favored localities where conditions of labor and 

 markets are just right. 



It may be urged that such a system once installed and 

 out of sight requires little further attention; whereas sur- 

 face irrigations require a large annual cost for the upkeep 

 of ditches and the actual spreading of water over the 

 land. This advantage is, however, more apparent than 

 real. Leaks are often sprung in the underground systems 

 which are located with difficulty and remedied at large 



