THE MINERAL CONSTITUENTS OF THE SOIL SOLUTION 4! 



cause of the practical impossibility of extracting the actual soil 

 solution, an empirical method was employed. Areas were se- 

 lected where good and poor crops were growing near each other 

 on the same soil types, and preferably in the same field. Sam- 

 ples of soil from under these crops were taken at several inter- 

 vals during the growing season, quickly removed to a nearby 

 laboratory, shaken thoroughly with distilled water in the pro- 

 portion of one part of soil to five parts of water, allowed to 

 stand twenty minutes and the supernatant solution passed through 

 a Pasteur-Chamberland filter. 1 



As has been pointed out above, the aqueous extract of a soil 

 thus arbitrarily prepared has no definite or casual relation to 

 the soil solution in the field. It is certain that the solutions 

 would not generally be the same. It should also be emphasized 

 that such a procedure can not, as some investigators have as- 

 sumed, afford a criterion between soluble and insoluble salts in 

 the soil, else the proportion of water to soil used above some 

 minimum would be immaterial as far as the amounts which 

 go into solution are concerned. The proportion of water to 

 soil is not immaterial, however, considering the chemical nature 

 of the soil components and the results of experiment. Con- 

 sequently, it is clear that the concentration of the soil solu- 

 tion is not simply the ratio of the amounts found in the aqueous 

 extract, to the percentage of moisture in the soil, but something 

 quite different. 



Artificial solutions prepared in the manner described above 

 should, however, furnish evidence as to whether or not there 

 are recognizable differences in the soluble mineral constituents 

 of good and poor soils respectively; and if such differences exist, 

 whether they are consistent. That is to say, if the more pro- 

 ductive soils also uniformly yield aqueous extracts of a higher 

 concentration, then it would be a fair inference that their natural 

 soil solutions are maintained at a higher concentration than in 

 the less productive soils. 



1 Capillary studies and filtration of clays from soil solutions, by 

 Lyman J. Briggs and Macy H. Lapham, Bull. No. 19, Bureau of Soils, 

 U. S. Dept. Agriculture, 1902 ; Colorimetric, turbidity and titration methods 

 used in soil investigations, by Oswald Schreiner and George H. Failyer, 

 Bull. No. 31, Bureau of Soils, U. S. Dept. Agriculture, 1906. 

 4 



