72G STATE BOARD OF AGRICULTURE. 



being rather appreciable in some of them and quite small in others, and 

 this variation did not bear a close connection to the previous fertilizer 

 treatment. In other words, there was no close relationship in all the 

 groups of soils, between the amount of material that went into solution 

 and the previous fertilizer treatment. These results are in general 

 agreement with those of the single salt-treated soils. 



Even when these same experimental field soils were kept at the opti- 

 mum moisture coutent. and placed outdoors under natural conditions, 

 failed to give a solubility product which bore a close relation to the 

 previous fertilizer treatment. Again, even at the optimum moisture 

 content the rate of solubility was very slow, but the extent of solubility 

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



The results of both series of studies of the field experimental soils go 

 to emphasize the principle already announced that the solubility factor 

 is not an absolute and reliable criterion of the state of fertility or crop- 

 producing power of soils. 



In the soils treated with acids of HNO3 HCL, H.SO,, H,PO„ Il,C.O,, 

 HO0H3O,, and CoHgO-, and washed and their moisture content was 1 of 

 soil to .7 of water and kept at room temperature, their rate of solubility 

 was quite rapid, but their extent of solubility varied, being very small in 

 the case of the inorganic and slightly higher in the phosphoric acid, and 

 quite appreciable in the organic acids. 



In the natural or untreated soils, which were washed, kept at room 

 temperature and at a moisture content of 1 of soil to .7 of water, both 

 the rate and extent of solubility varied considerably between the differ- 

 ent soils. In some soils both were rather appreciable, in others they 

 were very slight. In these soils, which numbered about 50, and included 

 nearly all the different classes and many types, there was no close and 

 consistent relationship between the solubility factor and the class of 

 soil, the organic matter content and the fineness of particles. 



Practically the same type of results were obtained in these various 

 types and classes of untreated soils when an optimum moisture content 

 was employed and the soils were kept outdoors under natural conditions. 

 In some soils more material went into solution when the moisture con- 

 tent was 1 of soil to .7 of water than when the ^lloisture content was at 

 optimum. 



On the whole there was a closer relationship between the solubility 

 factor and the state of fertility or crop producing power when the mois- 

 ture content was 1 of soil to .7 of water than when the moisture content 

 was at optimum. 



When natural soils, previously washed, and having a moisture con- 

 tent of 1 of soil to .7 of water, were kept at a temperature of 53 °C their 

 rate of solubility was somewhat appreciably increased. In some soils, 

 however, these factors were not at all affected by the high temperature. 

 The solubility of many soils even at this high temperature continued for 

 a long time, even GO daj's, but usually it became constant at the end of 

 about 30 days. 



At the ratio of 1 of soil to 5 of water the rate of solubility of natural 

 soils is also slow and the extent of solubility extremely small. In fact, 

 the amount of materi'il that went into solution at this water content is 



