ix.] EVILS DUE TO IRRIGATION 247 



tendency of the sterile spots to spread and the alkali to 

 be brought to the surface as soon as irrigation water is 

 employed, for without irrigation agriculture is hardly 

 possible. Many districts, which at first carried good 

 crops and were even laid down in fruit or vines, have been 

 ruined through the rise of alkali to the surface brought 

 about by irrigation ; in fact, in all these arid regions it 

 becomes exceedingly dangerous to raise the water table 

 in the land anywhere near the surface, because capillarity 

 then causes a rise of the salt changed water, and evapora- 

 tion concentrates it on the top. Just as some of the worst 

 alkali land occurs where rain falling upon the surround- 

 ing mountains finds its way by seepage through the 

 subsoil rich in salts and then rises to the surface in the 

 dry basin areas below, so the introduction of irrigation 

 canals pouring large volumes of water upon the land, 

 may equally establish the capillary connection between 

 the subsoil salts and the surface. The following extract 

 from Bulletin No. 14, U.S. Dept. of Agric, Div. of Soils, 

 dealing with alkali soils in the Yellowstone Valley, 

 shows the evil effects of incautious irrigation : — 



" Irrigation has been practised for twelve or fifteen 

 years. The water for the main ditch supplying the 

 valley is taken out of the river nearly 40 miles above 

 the town of Billings. When the country was first settled, 

 and indeed above the ditch at the present time, the 

 depth to standing water in the wells was from 20 to 50 

 feet, and there was no signs of alkali on the surface of 

 the ground. Under the common practice of irrigation, 

 however, an excessive amount of water has been applied 

 to the land, and seepage waters have accumulated to 

 such a degree that water is now secured in wells at a 

 depth of from 3 to 10 feet in the irrigated district, while 

 many once fertile tracts on the lower levels are already 

 flooded, and alkali has accumulated on them to such an 



