AVAILABILITY OF PLANT NUTRIENTS 331 



PERCENTAGE OF CONSTITUENTS NOT SOLUBLE IN HCL, 

 1.115 SP. GR. 



232. Significance of a strong hydrochloric acid analysis. 

 - This method of analysis was originally thought to 



give some indication of both the permanent fertility and 

 the immediate manurial needs of a soil ; but for each 

 question the accuracy of the deductions is limited by a 

 number of conditions that make it impossible invariably 

 to predict from an analysis how productive a soil may be 

 or what particular manure may be profitably applied. 

 It is very apparent that the chemical composition of a 

 soil is only one of the many factors affecting its produc- 

 tiveness. Unfortunately, not all the factors are under- 

 stood, and consequently these unknown ones cannot be 

 determined either qualitatively or quantitatively. If 

 it ever becomes possible to determine quantitatively all 

 the factors entering into soil productiveness in the field 

 condition, the problem will be solved. 



233. Relation of texture to solubility. The ratio of 

 sand to clay in a soil, and the distribution of the fer- 

 tilizing materials in these constituents, will affect the mini- 



