THE CHEMICAL COMPOSITION OF SOILS 



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oxides, the acid and basic constituents may form various 

 compounds as : 



Calcium 



Potassium . 

 Sodium . 

 Magnesium . 

 Iron 



Silicate 



Phosphate 



Chloride 



Sulphate 



Carbonate 



The following reactions will explain some of the more 

 elementary combinations : 



CaO + SiO 2 = CaSiO 3 CaO + N 2 O 5 = Ca(NO 3 ) 2 



3CaO + P 2 5 = Ca 3 (P0 4 ) 2 K 2 O + SO 3 = K 2 SO 4 



CaO + SO 3 = CaSO 4 Na 2 O+ SO 3 = Na 2 SO 4 



CaO + CO 2 = CaCO 3 MgO + SO 3 = MgSO 4 



It is often difficult to determine with accuracy the 

 exact form or combination in which an element is 

 present in the soil. When reported as the oxide, bases 

 may be considered as combined with any of the ox- 

 ides of the acid-forming elements, as indicated by 

 the reactions, to form salts. Each compound of 

 an element may have a different value as plant food, 

 hence it is important to determine as far as possible 

 the form or solubility of the various elements of plant 

 food. 



