66 DRY-FARMING 



pure water could do. A study of the composition 

 of the drainage waters from soils and the waters of 

 the great rivers shows that immense quantities of 

 soluble soil constituents are taken out of the soil 

 in countries of abundant rainfall. These materials 

 ultimately reach the ocean, where they are and have 

 been concentrated throughout the ages. In short, 

 the saltiness of the ocean is due to the substances 

 that have been washed from the soils in countries 

 of abundant rainfall. 



In arid regions, on the other hand, the rainfall 

 penetrates the soil only a few feet. In time, it is 

 returned to the surface by the action of plants or 

 sunshine and evaporated into the air. It is true 

 that under proper methods of tillage even the light 

 rainfall of aritl and semiarid regions may be made to 

 ]3ass to considerable soil depths, yet there is httle 

 if any drainage of water through the soil into the 

 standing ground water. The arid regions of the 

 world, theref(_)re, contribute proportionately a small 

 amount of the substances which make up the salt 

 of the sea. 



Alkali soils. — Under favcjrable conditions it 

 sometimes happens that the soluble materials, which 

 would normally be washed out of humid soils, accu- 

 mulate to so large a degree in arid soils as to make 

 the lands unfitted for agricultural purposes. Such 

 lands are called alkali lands. Unwise irrigation in 

 arid climates frequently produces alkali spots, but 



