SOILS AND FERTILIZERS 



252. 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 as explained in the chapter on 

 fixation. The extent to which potash may be liber- 

 ated by lime depends upon the firmness of chemical 

 combination 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 re- 

 sults are as follows : 69 



Kilos per hectare. 



In crop not litned. In limed crop. 



First Second First Second 



year. year. year. year. 



Lime 32.2 32.2 79.4 102.8 



Potash 26.7 28.6 95.6 97.2 



Phosphoric acid n.o 7.0 24.2 22.9 



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 Occasionally applications of superphosphate 

 fertilizers give large yields due to the gypsum which 

 they contain, and not to the phosphorus. 



253. Quicklime and Slaked Lime. When it is de- 

 sired to correct acidity slaked lime is used. Air- 

 slacked lime is not as valuable as water-slaked lime. 

 Quicklime cannot be used on land after a crop has 



