CONCENTRATION BY IRRIGATION WATER 31 



by the improper use of irrigation water. The author (8) 

 and many other workers have shown that the soluble salts 

 are carried through the soil very readily by irrigation 

 water. In some soils, like those in parts of the large in- 

 terior valleys of California, the original^ salt content, 

 though high, was not sufficiently high to prohibit the 

 growth of crops. After irrigation the salts are leached 

 from the higher land and carried to the lower, here to be 

 concentrated at the surface until the amount becomes too 

 great for ordinary crops to grow successfully. This con- 

 dition is found to an extent in practically every large 

 irrigated section of the world. Methods of preventing 

 accumulation in this way will be more fully discussed in 

 a later chapter. 



Considerable salt may also be added directly to the 

 land by the use of irrigation water carrying large quantities 

 of soluble salts. This method of contamination is dis- 

 cussed rather fuHy in Chapter XV. 



Relation of Origin to Methods of Treatment. An 

 understanding of the origin of the alkali in a given area 

 is essential to an intelligent treatment of the condition. 

 This is as true in handling a soil as in treating a human 

 disease. A physician who would give a remedy for a 

 headache without seeking the cause of the trouble might 

 entirely fail in curing. He might in any case give some 

 simple treatment that would be harmless, but a really 

 intelligent treatment would be founded on a knowledge 

 of the cause of the trouble. Likewise in handling alkali 

 land the source of the salt should be known. 



In one region an irrigation canal passed through a shale 

 hill that was very high in soluble salts. Large quantities 

 were dissolved and taken directly into the stream. Seepage 

 was also excessive and much alkali was carried to the 



