xviii CONTENTS 



CHAPTER X. FARM IRRIGATION 



PAGE 



The present extent of irrigation ..... 233 



In foreign countries . . . . . . 233 



In the United States 233 



The area in the United States that can be irrigated . . 234 

 The objects of irrigation . . . . . .236 



To remedy a deficiency in rainfall . . . .236 



To enrich the land . \ 237 



To correct alkali and improve texture . . . .237 



How far the natural water supply will go depends upon . 237 



The minimum amount of rainfall needed . . .238 

 The season when it falls . . . . .238 



The retentiveness of the soil ..... 238 



Irrigation in humid regions ...... 239 



Used to supplement deficiency in summer rainfall . 239 



Under what conditions it will pay \ ... 240 



Better tillage may obviate the necessity for irrigation . 241 



The supply of water for irrigation . . . . 243 



From streams . . . . . . 243 



From ponds and lakes . . . . .243 



From springs-and wells ...... 244 



Hydrant water ... . . . . . 244 



The construction of small earth reservoirs .... 245 



Pumping water for irrigation . . . . .246 



With windmills 247 



With steam and gasoline engines .... 248 



With water wheels . . . . . .249 



With hydraulic rams ...... 250 



The sluice gate 250 



Building distributing ditches . . . . . .251 



The use of flumes and pipes . . . . - . . 252 



Cement-lined ditches ....... 252 



Methods of applying water ...... 253 



A'local and personal problem ..... 253 



Check flooding ' . . . ' . . . . 254 



Wild flooding ... . . . .256 



Irrigation by furrows ....... 257 



Sub-irrigation . . . . . . . . 260 



Methods of measuring water . . . . . . 262 



The divisor . . 262 



The module 263 



By apportionment ....... 263 



Units in measuring water ...... 263 



