EXPETtTMEXT STATION lUTTJ-F/riNS. 707 



niul even the salt of Ca(N();>).3 tends to have a deju'essiiig effect upon (he 

 solnhilit}' of soils. (2) A liiiili concentration also tends to have a de- 

 pressing ellcct n])on tlie solubility of soils. (8) The soil material going 

 into solntion is slow in rate and small in annnint and nnless the soil 

 is very heavily fertilized or is exceedingly rich its rate and extent ol" 

 solnhility is not very nnicli different from that of a medium productive 

 soil. (4) The productivity or fertility of a soil is not determined only 

 by the amount ol" material going into solution but also by (he kind of 

 material, i. e., whether it is composed of all the essential plant food ele- 

 ments and i)robal)ly in the proper amounts; and (5) The plant exerts 

 probably itself some influence in obtaining plant food directly from the 

 soil particles. 



It is rather surprising to note that there is a closer connection between 

 the factor of solubility and crop productivity in the various soils when 

 the water content is maintained at a supersaturation point than at the 

 optimum point. 



Finally, it must be stated that the results of this i^hase of the investi- 

 gation go to emphasize the principle already announced that the solu- 

 bility factor is not always an absolute and reliable criterion for the state 

 of fertility of soils. A high solubility, however, may be generally re- 

 garded, but not always as indicative of high state of fertility. 



Kate and Extent of Solubility of Soils, Treated with Acids and then 

 Washed Until all the Free Soluble Acids were Eliminated. Rate of 

 Soil to Water was about 1 to .7 and Mixture Maintained at Room 

 Temperature. 



Having studied the effect of salt treatment upon the rate and extent 

 of solubility the desire arose to investigate the effect of acid treatment 

 u))ou the rate and extent of solubility. Accordingly, live different soils 

 were treated with seven different acids and washed until all the free 

 soluble acids were eliminated as indicated by the exceedingly small de- 

 pression of the freezing point of the washed soils. The washed soils were 

 then placed in the freezing point tubes, their water content being brought 

 to the ratio of about 1 of soil to about .7 of water and tlieir freezing 

 point depression determined immediately and as often, thereafter, as 

 was deemed necessary. The soils consisted of a clay loam, two brown 

 silt loams, one fine sandy loam and one sand. These soils are the same 

 as those used in the case of the salt treatments. The acids comprised 

 HNO3 nCl, H.SO^, n,rO„ 11,(^,0,, C,rr,0„ and C,,lf,0,. These acids 

 were used in tenth normal strength. The treatment consisted of treat- 

 ing 50 grams of air-dry soil with 150 c.c. of the acid, allowing the mixture 

 to stand for about 24 houi-s with occasional shaking, and then washing 

 the soil free of acids. The experimental data obtained in this phase of 

 the general investig;ition are shown in tables 17 to 20 inclusive. 



