EXPERIMENT STATION BULLETINS. 725 



of these salt treaments rose only from about .007° to .015°C or from 175 

 to 375 parts per million. As a general rule the NaXOg and NaCaHgOa 

 treatments in all the soils, except sand, tended to yield the greatest 

 solubility product, the CaNO.,, KJIJ*0^ and CaH, (PO.J, the smallest 

 and the KNO.,, KCL, K,SO,,' lNHJ,vSO^ and MgSO, an intermediate 

 In manj^ soils the CaH^ (1^04)2 and in a few cases the Ca(N03)2 and 

 KH2PO4 treatments did not only give the smallest concentration but 

 even a smaller concentration than the check. Evidently these salts 

 tended to have an indifferent or depressing effect upon the solubility 

 of soils. As a whole it appears that the phosphates tend to depress 

 solubility and that they probably act as conservers of bases under field 

 conditions. 



The results of solubility of these singly salt treated soils go to indicate 

 that a salt or fertilizer treatment leaves a residual effect upon the soil 

 and this residual effect continues to be manifested in increased solubility 

 and in increased crop-producing power. 



These data also go to indicate that the reaction between soils and 

 salts seems to be chemical and not physical. 



In view of the different residual effects that the different salts or 

 fertilizers have upon the solubility of soils and in view of many theo- 

 retical and practical considerations, the solubility factor cannot be con- 

 sidered an absolute or reliable criterion for the state of fertility or crop- 

 producing power of soils. In general, however, it can be said that a 

 very heavily fertilized or extremely rich soil gives a greater solubility 

 product than an unfertilized or poor soil. 



Although the solubilitv attains a constancy at the end of about 60 

 days this constancy is not a true equilibrium. In other words, the solu- 

 tion is not saturated when solubility ceases. This is proven by the fact 

 when different proportions of soil and water are employed an apparent 

 equilibrium is attained in all the ratios and yet the solubility product 

 is not at all the same when the equilibrium is reached, and it does not 

 become the same no matter how long the soil and water in the different 

 ratios are kept in contact. Furthermore, a consideration of the char- 

 acter of the soil makes it extremely doubtful if true equilibrium can ever 

 be attained in the soil solution. 



Tlie solubility process of the soils would undoubtedly go on for a long 

 time and probably almost indefinitely, in view of the extremely slow 

 rate of solubility, if some factors did not intervene. 



When different soils were treated with a combination of salts includ- 

 ing CafXO,),, XaNO,, KNO. KCL, K,SO,. (NH.^.SO^. MgSO;, KH.PO^ 

 CaH^(PO, !._, and NaC2ll302 and washed and kept under the same condi- 

 tions as the preceding, their rate of solubility was also slow, but the 

 extent of solubility was very appreciable. In this combination the phos- 

 phates did not depress the solubility very markedly, but when the 

 (NH^loSOa and NaCoH^Oo salts were left out from the combination then 

 the depression became more marked. 



When exDcrimental field soils from the Experiment Stations of Illinois, 

 Cornell, Phode Island and Ohio, which had been receiving fertilizer 

 troatmoiits in tlio usual way. were washed, and kept at the moisture 

 ('(nitcnt of 1 of soil to .7 of water and at room temperature, their rate 

 of solubility was also very slow, but their extent of solubility varied, 



