CHAPTER V 



FIXATION 



164. Fixation, a Chemical Change. — When a fertil- 

 izer is applied to a soil chemical changes take place 

 between the soil and the fertilizer. Theie is a general 

 tendency for the soluble matter of fertilizers to undergo 

 chemical changes and become insoluble. This pro- 

 cess is known as fixation. If a solution of potassium 

 chloride be percolated through a column of clay, the 

 filtrate will contain scarcely a trace of potassium chlo- 

 ride, but instead calcium and other chlorides. In its 

 action upon the soil, the potassium chloride has un- 

 dergone a chemical change, the element potassium 

 being replaced by the element calcium. An ex- 

 change has taken place between the two bases. 



165. Fixation Due to Zeolites. — It has been shown 

 by experiments, particularly by Way and Voechler, 

 that fixation is due mainly to the zeolitic silicates. 52 

 Sandy soils containing but little clay have only a fee- 

 ble power of fixation. Clay soils when digested with 

 hydrochloric acid to remove the zeolitic silicates, lose 

 their power of fixation. The fixation of potassium 

 chloride and the liberation of calcium chloride may be 

 illustrated by the following reaction : 



