LIME AND MISCELLANEOUS FERTILIZERS 199 



have such strong power of endurance that they are 

 able to thrive in the presence of acids. The charac- 

 ter of the weeds frequently reflects the character of the 

 soil as to acidity, in the same way that an "alkali' 

 soil is indicated by the plants produced. 



250. Lime Liberates Potash. — The action of lime 

 upon soils well stocked with potash results in the fixa- 

 tion of the lime and the liberation of the potash ; the 

 reaction takes place in accord with the well-known 

 exchange of bases. The extent to which potash may 

 be liberated by lime depends upon the firmness with 

 which the potash is held in the soil. Boussingault 

 found that when clover was limed there was present 

 in the crop three times as much potash as in a similar 

 crop not limed. His results are as follows : 68 



The indirect action of land plaster upon Western 

 prairie soils in liberating plant food, particularly 

 potash and phosphoric acid, is unusually marked. 

 Laboratory experiments show that small amounts of 

 gypsum are quite active in rendering potash, phos- 

 phoric acid, and even nitrogen soluble in the soil 

 water. 5 



