18 



X. H. AGR. EXPERIMENT STATION. 



[BuUetin 170 



This data shows that large amounts of potassium are taken 

 up and held by the soils. Also, that the amount of potassium 

 so held increases with increase in the clay content of the soil. 

 If di-potassium phosphate is substituted for potassium chloride 

 under the above conditions, the following results are observed: 



Table X 



An examination of the water extract of the soil treated with 

 potassium chloride shows that the solubihty of the acid radical 

 is not affected by the soil. All the chloride appears in the solu- 

 tion as potassium chloride or as the acid radical of new salts. 

 The new salts are chiefly chlorides of calcium, magnesium and 

 sodium. If the acid radical is the sulphate or nitrate, the same 

 conditions of solubility occur. A possible exception is the case 

 where more calcium sulphate is formed than can dissolve in the 

 given volume of water. 



Salts of iron and aluminum must in some cases be formed in 

 these reactions. Their rare appearance in the solution is prob- 

 ably due to alkalinity of the water extract which in many in- 

 stances is sufficient to cause these salts to hydrolyze and the 

 bases to reprecipitate. 



Different conditions of solubihty are observed in the case of 

 the phosphates. The extent to which they are taken from solu- 

 tion and retained by the soil is shown in Table XI on page 19. 



When soils react with potassium chloride, nitrate, and sulphate, 

 the reaction must be chemical, because the amounts of new salts 

 which appear in the water extract are equivalent to the amount 

 of potassium removed. When soils react with potassium phos- 

 phate, both the base and acid radical are removed from solution. 



