1919] ' SOILS — FERTILIZERS. 513 



and KNO3, KCl, KaSOi, (NH4)2S04, and MgSO* an intermediate product. In 

 many soils CaH4(POi)2, and in a few cases, Ca(N03)2 and KH^PO* did not 

 only give the smallest concentration but even a smaller concentration than the 

 check, indicating that these salts have an indifferent or depressing effect upon 

 the solubility of soils. As a whole it appeared tliat the plaosphates tend to de- 

 press solubility and tliat tliey probably act as couservers of bases under field 

 conditions. 



" Tlie result of solubility of these singly salt-treated soils goes 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 tlie reac- 

 tion between soils and salts seem to be chemical and not physical. In view of 

 the different residual effects tliat the different salts or fertilizers liave upon 

 the solubility of soils and in view of many theoretical and practical considera- 

 tions, the solubility factor can not be considered an absolute or reliable criterion 

 for the state of fertility or crop-producing power of soils. In general, liowever, 

 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 solubility attained a constancy at the end of about 60 days, 

 this constancy is not believed to be a true equilibrium, the solution not being 

 saturated when solubility ceases. This is said to be demonstrated by the fact 

 that when different proportions of soil and water are employed 'an apparent 

 equilibrium is attained in all the ratios, while the solubility product is not 

 at all the same when the equilibrium is reached and does not become the same 

 no matter how long the soil and water in tlie different ratios are kept in con- 

 tact. Furthermore, considering the character of the soil, it is deemed ex- 

 tremely doubtful if true equilibrium can ever be attained in the soil solution. 

 It is also stated that the solubility process of the soils would undoubtedly go 

 on for a long time, 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, including 

 Ca(N03)2, NaNOs, KNOs, KCl, RSO*, (NHi)2S0*, MgSO, KHsPOs CaH4(P04)2 

 and NaC2H302, and washed and kept under the same conditions as indicated above 

 their rate of solubility was also slow, but the extent of solubility was very 

 appreciable. The phosphates in this combination did not depress the solubility 

 very markedly, but when (NH4)2S04 and NaC2H302 were omitted the depression 

 became more marked. 



Experimental field soils from the Illinois, New York Cornell, Rhotle Island, 

 and Ohio Experiment Stations, which had been fertilized in the usual way, 

 were washed and kept at a moisture content of 1 of soil to 0.7 of water and at 

 room temperature. Their rate of solubility was very slow but their extent of 

 solubility varied, being rather appreciable in some of them and quite small in 

 others, and the variation failing to bear any close connection to the previous 

 fertilizer treatment. These results were in general agreement with those of the 

 single salt-treated soils. Even when these soils were kept at an optimum mois- 

 ture content and placed outdoors under natural conditions, they failed to give 

 a solubility product which bore a close relation to the previous fertilizer treat- 

 ment, the rate of solubility being very slov/ and the extent of solubility quite 

 appreciable but far smaller than that of the salt-treated soils. 



Soils treated with HNO3. HCl. H^SOi, H3PO4, H2C2O4, HC2H3O2, and CoHsOi, 

 washed, maintained at a moisture content of 1 of soil to 0.7 of water, and kept 

 at room temperature showed a quite rapid rate of solubility, although the extent 

 of solubility varied, being very small in the case of the inorganic acids, slightly 

 higher with phosphoric acid, and quite appreciable with the organic acids. 



