EXPERIMENT STATION BULLETINS. 323 



As shown in Table 2, the quantities of potassium fixed from the KCl 

 solutions by this second series of soils were closely equivalent to the quantities 

 of calcium and magnesium found in the solutions. An attempt was made 

 to determine sodium in the solutions from the clay loam soils but the quan- 

 tities of this element present were considered too small for quantitative 

 gravimetric determination and hence relatively insignificant. The soil 

 solutions obtained in this experiment were also alkaline to red litmus paper 

 but it was not necessary to consider that iron, aluminum or sodium were 

 present in the solutions combined with chlorine in order to account for prac- 

 tically all of the chlorine in the solutions not combined with potassium; the 

 quantities of calcium and magnesium found were very nearly sufficient for 

 this purpose. The reaction was apparently chiefly between the KCl solutions 

 and the calcium and magnesium of the soils. 



All the alkahne soils except the clay loam showed greater fixation of potas- 

 sium and more calcium and magnesium in their solutions than did the acid 

 soils of the same class. The increase in the fixation of potassium shown by 

 the acid clay loam over the other member of this class, however, was accom- 

 panied by a corresponding increase in quantity of calcium found in its solution, 

 and this effect may also be notes in subsequent exj^erimcnts with these clay 

 loam soils where fixation apparently depends on soil calcium. Treating the 

 soils with HCl and then washing thoroughly with distilled water greatly 

 lowered the degree of fixation of potassium as shown in Table 2. This effect 

 was considered to be due to the removal of calcium and magnesium by the 

 acid treatment. These results also strongly indicate that soil calcium and 

 magnesium may be the principal cause of fixation of potassium in the soils 

 under experimentation. 



The conclusion seems justified that the reaction was practically entirely 

 between the neutral salt solution and calcium and magnesium of the soils 

 in a silicate combination. The soil factor determining the degree of fixation 

 of potassium is apparently the quantity of calcium and magnesium in the 

 soils in condition to react with the salt solution, the soil calcium having by 

 far the greater influence. It is recognized, however, that certain soils may 

 contain other elements in replaceable combinations and the proportions of 

 these elements may vary, and also, results may vary with varying concentra- 

 tions of salt solutions. 



Fixation of Potassium from K2SO4 and KNO3 and of Ammonia from 



(NH,)2S04 



Other salts of potassium, namely, K2SO4 and KNO3 and also (NH4)2S04 

 were used in a manner similar to KCl in order to study their effects on the 

 series of different soil classes. Table 3 contains the results of this phase of 

 the subject. 



Attention is called to the principal features of the results presented in Table 

 3, as follows: Fixation of potassium from K0SO4 and KNO3 was closely 

 equivalent in quantity to that fixed from KCl by these soils and the quanti- 

 ties of soil calcium exchanged were also closely equivalent. Quantities of 

 NH4 fixed, however, were not closely equivalent to those of potassium fixed 

 from the salts used, being somewhat smaller, and were also not in similar 

 agreement with the quantities of calcium exchanged, although quantities of 

 calcium liberated by the NH4 - ion were closely comparable to those found 

 in the solutions from the potassium salts treatments. While differences must 

 b« recognized between the effectfi of the potjissium and ammonia in the experi- 



