EXPERIMENT STATION BULLETINS. 00?, 



In treating the soils with salts there were many objects in \ie\v. 

 Besides measuring the rate and extent of solubility of the treated soils 

 it was desired to study at least three other subjects, namely, il"} residual 

 effect of salt or fertilizer treatment upon the rate and extent of solu- 

 bility of soils; (2) the possibility of employing the solubility factor as a 

 criterion for the state of fertility of soils, and thereby distinguishing 

 between good and poor soils, and (3) the character of the reaction be- 

 tween soils and salts, i. e., whether it is chemical or physical. 



As to the first subject the experimental results presented show that 

 with the exception of CafNO;,),, KH,PO„ and CaH.lPOJ. all the other 

 salts, which include NaNO, KNO3, KCl, K,SO„ (NHJ.SO,, MgSO,, 

 and NaCgHjOa, leave a residual effect upon the soils which is mani- 

 fested by the long and rather large anionnt of material going into solu- 

 tion in all the soils, except in sand. This residual effect goes to prove 

 that when a soil is treated with a soluble salt a certain combination 

 takes place between the soil and the salt or its ions, that upon wash- 

 ing, this salt or its ion is not carried away and that in this couibiua 

 tion the solubility of the soil is changed. These experimenfal lads 

 confirm the validity of the various practical observations that when a 

 soil is treated with solulde fertilizers the fei'tilizer is not all washed 

 away but leaves a residual effect which persists for a long time, as mani- 

 fested by the continued increased growth of crops. Witness, for in- 

 stance, the residual effects of the various fertilizers at the Rothamsted 

 Experiment Station. 



Because the salt treatments of Ca(NO,)o, KH,PO, and CaH,(PO,),, 

 did not cause an increase in solubility of soils, it cannot be concludecl 

 that these salts did not leave a residual effect upon the soils. These 

 salts did also leave a residual effect upon the soils, but their residual 

 effect apparently is not shown in the solubility of the soils, but if is 

 in the crop production. 



As to the second subject, the experimeutal data also show that the 

 solubility factor nuiy be taken as a criterion for the state of fertility 

 of a soil, and consequently for distinguishing between a rich ;nid a poor 

 soil. As will be seen, the results sIiova^ that with the exception of the 

 salt treatments of Ca(N(),).„ KH.PO,, and (^all^(P();).. all the other 

 salt treatments caused a considerable increase in the solul)ility product 

 over the check. In many cases the increase is over .070 'rC freezing point 

 depression or 1750 parts per million of solution. From these marked 

 increases in the solubility product over the check it would be logically 

 inferred that a heavily fertilized or very rich soil gives more material 

 to solution than an unfertilized or poor soil. 



The last inference or conclusion, however, cannot be rigidly adhered 

 to. On account of the exceptions already mentioned and a few others 

 to be mentioned later on, it cannot be claimed that the solubility factor 

 is an al)solute and reliable criterion of the fertility of a soih As a 

 matter of fact it is not only the amount of material that goes readily 

 into solution which makes a soil fertile, but also the kind of material 

 that goes into solution. As it is now understood the soil solution must 

 be properly balanced in the various food elements used by the plant, in 

 order that a soil may be really called a fertile soil. If the material that 

 goes into solution does not form a properly balanced plant food medium, 



