Chapter III. 



SOU ANALYSIS AND THE HISTORICAL METHODS 

 OF SOIL INVESTIGATION. 



Owing to the labors of Davy, Boussingault, de Saussure, 

 Liebig, Sachs, Knop, Salm-Horstmar, and others scarcely less 

 distinguished savants, it has been clearly shown that growing 

 plants need certain mineral elements in order to maintain their 

 metabolic functions, and that these mineral elements can be ob- 

 tained, under normal conditions, from the soil. All subsequent 

 investigation has confirmed these statements and they can now 

 be accepted as facts with as much assurance as any known law of 

 nature. 



The determination and formulation of these two fundamental 

 facts came at a time when analytical chemistry was being rapidly 

 developed and was finding wide and useful applications in numer- 

 ous fields of activity. It was natural, therefore, that analytical 

 chemistry should be enlisted in this new field of work, obviously 

 of the first importance to the welfare of mankind. It was early 

 found, however, that the chemical analysis of a soil fails to ex- 

 plain its relative productivity. In other words the content of a 

 soil with respect to potash, phosphoric acid, or other mineral 

 plant-food constituent, bears no necessary relation to its crop- 

 producing power. Many cases were found where one soil 

 "analyzed well" but did not produce as large a crop as another 

 soil which "analyzed poor." 1 To meet this difficulty a subsidiary 

 hypothesis was brought forward, which rapidly gained general 

 acceptance although lacking experimental support. 



This hypothesis supposes that the mineral constituents of the 

 soil are present in two different chemical conditions or distinct 

 kinds of combinations, one of which readily gives up its con- 

 stituents to growing plants, while the other does not; and the 



1 See also, Die Aufnahme der Nahrstoffe aus dem Boden durch die 

 Pflanzen, von J. Konig und E. Haselhoff, Landw. Jahrb., 23, 1009, 1030 

 (1894). 



