272 Irrigation and Drainage 



HOW ALKALIES ACCUMULATE IN THE SOIL 



Everywhere in the soil where there are sufficient 

 changes in the air and the moisture, the soil grains 

 are being broken down and dissolved by both physical 

 and chemical means, and unless the rains are suffi- 

 ciently heavy to carry the ever -forming dissolved 

 salts away in the country drainage, they will be 

 brought to the surface by capillarity and there con- 

 centrated until precipitated. The more insoluble of 

 the plant -foods, and other salts which are not such, 

 cannot charge the water sufficiently high to do serious 

 harm, hence in common language and in the sense 

 the term is here used, they do not become "alkalies." 



But with the other salts the case is different. 

 They are precipitated when the solution becomes 

 strong enough, and form deposits on the surface or 

 about the roots in the soil where water is being re- 

 moved, but before this actually occurs one or both of 

 the actions referred to above begins to take place. 



In arid regions, where the alkalies proper are most 

 abundant, rains enough may fall to slowly carry for- 

 ward their formation, but not enough to carry them 

 out of the land. From the higher levels and steeper 

 slopes they are readily moved by surface drainage and 

 wind action to the lower lands, where the amount 

 may become so large as to form thick beds. During 

 the wet season of such countries, these salts may sink 

 into the soil, but to rise again when dry weather 

 restores the action of capillarity. 



In the humid regions, there is necessarily an even 



