270 THE PRINCIPLES OF SOIL MANAGEMENT 



deductions are limited by a number of conditions which 

 make it impossible 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 productiveness. Unfortunately, not 

 all of the factors are understood, and consequently 

 these unknown ones cannot be determined either quali- 

 tatively or quantitatively. If it ever becomes possible 

 to determine quantitatively all of the factors entering 

 into soil productiveness in the field condition, the prob- 

 lem will be solved. 



130. Permanent fertility, and manurial needs. 

 Permanent fertility can best be judged by the complete 

 analysis of the soil, but, with the exception of potash, 

 the possible deficiency the constituents likely to be 

 required in manures may be judged from the hydro- 

 chloric acid solution with a fair degree of accuracy. 



Conclusions as to the manurial needs of the soil are 

 confined to ascertaining whether any constituent is 

 present in such small amount as to furnish an inadequate 

 supply for crop production. If, for example, a certain 

 ingredient is found to be present in very small amount, 

 it may be concluded that the addition of a manure con- 

 taining this substance would be profitable; but there is 

 considerable difference of opinion among analysts 

 as to what this figure is for each of the ingredients. 

 This minimum amount may vary with certain conditions 

 of soil. 



131. Relation of texture to solubility. The relative 

 amounts of sand and clay in the soil and the distribution 



