134 AGRICULTURAL ENGINEERING 



system is not only expensive to install, but also quite extrav- 

 agant in many cases in the use of water. This is due to 

 the fact that the water tends to percolate downward from 

 the opening and so does not saturate the soil satisfactorily. 

 Spraying Method. Where irrigation is practiced in a 

 small way the water may be applied by spraying. This 

 system provides surface pipes containing water under 

 pressure, whch may be discharged through nozzles in such a 

 way as to cover the entire surface. Often the pipes are 

 arranged so as to revolve, turning the nozzles about in such 

 a way as to discharge in different directions and thus reduc- 

 ing the amount of pipe required. 



The Measurement of Water. Most of the water used 

 in irrigation is sold to the farm owners, which fact necessi- 

 tates that methods be devised for its measurement and regu- 



lation. In addition, 

 the irrigator should 

 know something defi- 

 nite about the amount 

 of water applied, in 

 order that he may de- 

 termine whether or 

 not it is being used as 

 efficiently as it should 

 be. 



Units of Measure- 

 ment. One of the most 



Fig. 77. A Cippoletti weir with water regis- ca-Hcfop-rnrv unite rf 



ter in place for measuring and recording the SatlSiaCtOry 



head of water over the lower edge of the weir, measurement f rom the 

 (Bui. 86, Office of Experiment Stations.) 



standpoint of the agri- 



culturist is the acre-inch, which is the amount of water required 

 to cover an area of one acre one inch deep. Thus, ten acre- 

 inches is sufficient water to cover an acre ten inches deep, 



