Nov. II, 1918 Determining the Absolute Salt Content of Soils 



335 



leached away, at least from the upper layers, and the salt content falls 

 again to the depression of about 0.010° C, or 250 p. p. m. at the surface. 

 In the cropped soils the salt content is, as a rule, quite low, amounting to 

 a depression of only about 0.010° C, or 250 p. p. m. at the various 

 depths, as compared to a depression of about 0.200° C, or 4,878 p. p. m. 

 in adjacent bare soil at the surface. Again, after a long drouth the salt 

 content of nearly all bare soils varies considerably at different depths. 

 The variation may range from about 5,000 p. p. m. at the surface to 

 about 250 p. p. m. at the third inch. All these facts find ample con- 

 firmation in the data presented in Table II, which shows the salt content 

 of a certain number of soils under the conditions described above. The 

 salt content is expressed both in freezing-point depression and parts 

 per million of solution. 



Table II. — Salt content and freezing-point lowering of soils at different seasons, at 

 different periods, under different cultural condiiiofis, and at different depths 



It is evident, then, that the salt content of soils is controlled by many 

 external factors, and that v/hen these factors are not taken into con- 

 sideration in the collection of the soil samples and in the interpretation 

 of the results, very erroneous conclusions will inevitably be drawn as 

 to the comparative salt content of soils. Yet it is surprising how many 

 investigators in the past have overlooked or ignored these factors and 



