198 



BACTERIA AND SOIL FERTILITY 



jurious action of alkalies in a soil may at times be neutralized by 

 a balancing of the soil solution, that is, the addition of a second 

 salt which would offset the effect of the one present in the soil. 

 This is possible to a limited extent. For instance, calcium, mag- 

 nesium, or even iron salts have been added to an alkali soil and 

 their bacterial flora greatly improved. This method, however, is 



Fig. 40. — Influence of alkali on growth of crimson clover. 

 Reading from left to right: (i) normal soil, (2) soil leached, 

 (3) leached + 15T manure, (4) soil with 2 per cent sodium 

 chloride, (5) sodium chloride leached out, (6) soil with 

 sodium chloride + 15 tons manure, (7) leached + I5 tons 

 manure, (8) soil with sodium chloride + extract from fertile 

 soil, (9) leached + extract of fertile soil. 



in the experimental stage and too great reliance must not be 

 placed upon it in actual practice. 



Removing the Salt. — Several methods have been used with 

 varying degrees of success for the removal of the salts from 

 the soil: 



(1) By the growing of alkali-resistant plants on the soil. 

 These are harvested and removed. When the plants are pastured 

 from the soil no benefit would result. 



(2) In limited areas it has been found feasible to scrape up 



