Feb. II. r9i8 Freezing-Potfit Method and Soil Solution 383 



VARIOUS FACTORS AFFECTING THE SOIL SOLUTIONS 



As a result of the observations on the tank soils which have just been 

 described, it was decided to study various other factors possibly affecting 

 the depression of the freezing point. What conditions other than crop- 

 ping might increase or decrease concentration? The first step was to 

 study the soils which had been held in a nearly air-dry state in bins. The 

 results of these determinations have already been set forth in Table II, 

 and comparisons may now be made between tank soils and the correspond- 

 ing bin soils. It will at once be noted that a number of the latter show 

 very much higher concentrations of the soil solution than either the 

 cropped or the uncropped soils during most of the season. All three 

 portions of each soil were originally derived from the same sifted and 

 homogenous mass of soil. The existing dififerences must therefore be 

 due to subsequent treatments which are correlated with three levels of 

 concentration: (i) A very low concentration in the cropped soil, (2) a 

 higher one in the uncropped soil, and (3) highest of all in some of the 

 stored soils. The latter in a number of cases gave four or five times as 

 great a depression of the freezing point as the corresponding cropped soils. 

 The fact that the uncropped soils in the tanks had in some cases a less 

 concentration of the soil solution than the stored soils may be explained 

 by the treatment of the preceding year when both tank soils were cropped. 

 It may also be true that long storage of the bin soils under the special 

 conditions has brought about a decomposition of soil minerals as well as an 

 increase in nitrates, with the result that a more highly concentrated soil 

 solution is produced as soon as the soil is mixed with its optimum quan- 

 tity of water. The extractions of the bin soils confirmed the freezing- 

 point results. Water extracts showed a correspondingly high solubility 

 for nearly all constituents. 



With the establishment of the relations of freezing-point lowerings of 

 soils under several conditions it became of interest to make a somewhat 

 more detailed study in an effort to determine what factors are especially 

 active in changing the concentration of the soil solution. 



EFFECT OF INCUBATION ON CONCENTRATION OF SOIL SOLUTION 



The first experiments dealt with the effect of long standing at laboratory 

 temperatures. Samples were obtained from the tank soils, and after the 

 determinations of freezing-point lowerings portions were kept in tight 

 Mason jars for from one to three months. At the end of the specified 

 periods the freezing points were again determined, with the results given 

 in Table IV. 



