Mineral Nutrients 



151 



The following table shows the distribution of the sub- 

 stances mentioned in a few types of rocks : * 



Practically, no soil is made up of mineral constituents 

 in the same proportion as they occur in the original rock. 

 There are losses and gains of plant nutrients with respect 

 to any one type of rock, but residual soils, referable to the 

 decomposition of a particular rock, approach the rock 

 more nearly. In general, however, it is clear that, since 

 soils are formed by the grinding down and decomposition 

 of rocks, they may contain all the minerals of the earth's 

 crust. A soil is ordinarily of complex origin, and aside 

 from this, the chief qualities which make it a favorable 

 environment for the plant as contrasted with broken rock 



1 For a comprehensive treatment of the composition of original rock 

 and residual soils derived therefrom the student should consult the 

 following: Lyon and Fippin, "Soils," pp. 1-68; Bailey, "Cyclopedia of 

 American Agriculture," i (Chapter X) : pp. 323-371. 



