TREATMENT OF ALKALI LAND 227 



takes place from a wet soil during summer in such climates 

 as those of India or California, determines a rapid concen- 

 tration of the salt solution at the surface, resulting often in 

 the crystallization of the salt, and the covering of the soil 

 with a white crust. While however the soil beneath continues 

 moist, the salt accumulating at the surface will spread by 

 diffusion downwards, or be more rapidly carried in this direc- 

 tion by rain. The soil is in this manner enriched with salt 

 from the top, and a band of salt is formed below the surface 

 as shown in the right-hand column of Table XXXVIII. 



The irrigation of land by temporarily flooding the surface 

 with water was naturally at first regarded as an excellent 

 plan for removing alkali from the soil. In the case of a soil 

 provided with good natural or artificial drainage, the liberal 

 application of water at the surface, and its percolation through 

 the soil to the drainage outfall, would doubtless prove the 

 most effectual method which could be devised for freeing the 

 soil from alkali. Irrigation systems in India and California 

 have however been carried out without any provision being 

 made for drainage. The soils dealt with have also frequently 

 been of a close texture, slowly permeable to water ; and hard 

 pans, still more impervious to water, frequently occur two 

 or three feet beneath the surface. Under these circumstances 

 surface flooding produces no permanent benefit, and shortly 

 after it has ceased the accumulation of alkali at the surface 

 takes place as actively as before. Both in India and Cali- 

 fornia large districts have been irrigated from high-level 

 canals, without any provision being made for drainage from 

 the soil ; the result has been that the water level has been 

 brought nearly to the surface of the land, and some of the 

 lower lying fields converted into swamps. With this rise of 



