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 : 



Zeolite Zeolite 



H 2 O 4- CaCU. 



216. Humus may cause Fixation. Also other com- 

 pounds of the soil, as humus and calcium carbonate, 

 take an important part in fixation. In the case of 

 humus, a union occurs between the minerals in the 

 fertilizer and the organic acids formed from the decay 

 of the humus in the soil, resulting in the production of 

 humates. 



217. Variations in Fixative Power of Soils. All soils 

 do not possess the power of fixation to the same extent. 

 Heavy clays have the greatest fixative power, while 

 sandy soils have the least. As a general rule, soils of 

 high fertility show good fixative power. Hence it is 

 that a fertilizer, after being applied to a soil, may be 

 entirely changed in composition, so that the plant feeds 

 on the chemical products formed, rather than on the 

 original fertilizer. 



218. Fixation of Phosphates. - - The phosphates of 

 fertilizers readily undergo fixation by combination with 



