CHAPTER IX 



RELATION OF ALKALI TO PHYSICAL 

 CONDITIONS IN THE SOIL 



The entire physical condition of the soil is changed by 

 the presence of large quantities of certain soluble salts. 

 All salts in fact bring about some physical changes but 

 certain of the alkali salts, particularly the carbonates, 

 cause complete transformations. Each soluble salt that 

 is present in large quantity produces some typical con- 

 dition, which is usually bad. The effect of one salt may 

 be in part neutralized by another, so that the final effect 

 is somewhat uncertain. It depends on the nature of the 

 soil and on the combination and concentration of the salts 

 present. 



The chief manifestations of salts on the physical con- 

 dition of the soil are: (i) The change in structure or tilth; 

 (2) an altering of the colloidal substances; (3) the forma- 

 tion of a hardpan; and (4) a change in the moisture re- 

 lations. 



Changing Soil Structure. The tilth, or structure, of a 

 soil has much to do with its crop-producing power. Soils 

 containing an equal amount of plant-food may vary 

 greatly in their power to yield. The soil must do more 

 than furnish a supply of food for growing plants; it must 

 also be a good home for them. Plants, like animals, even 

 though they have sufficient food to nourish them will not 

 thrive unless other factors affecting growth are favorable. 



Air must be present for the roots, and the soil particles 



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