192 Fertilizers 



which control the profitable use of fertilizers are, therefore, 

 briefly discussed, in order to arrive at a better under- 

 standing of the practical suggestions and concrete examples 

 given in subsequent chapters. 



Derivation of soil a guide as to its possible deficiencies. 



The first consideration is the soil itself, and its influence. 

 It is well known that a wide difference exists in soils, both 

 in reference to their chemical character or composition, 

 and to their physical properties, each having a direct 

 influence in determining the effect of any specific applica- 

 tion of fertilizers. These differences in soils are due to 

 changes which were wrought in the surface of the earth 

 during its formation, and which are continuing in a small 

 way at the present time. It is believed that the original 

 earth crust contained all the minerals now found in it, but 

 that in the beginning they were distributed more uniformly 

 throughout its mass, and that the soils as they exist at the 

 present time, and as a result of the direct disintegration of 

 the original rock, represent a very small area of the earth's 

 surface. They are not now constant, but variable in their 

 character. The various changes that have taken place 

 during geologic time have resulted in the breaking up of 

 the original rocks, a part having been separated mechani- 

 cally and being represented by various sizes of particles, 

 and a part rendered soluble. The fragments and the 

 soluble portions thus separated have not been deposited 

 again in the same proportions as they existed in the original 

 rock, which has caused a very wide variation in the chemi- 

 cal composition of the different soil deposits. The process 

 and its results may be shown at the present time in the 

 wearing away of rocks. The harder, sandy particles sep- 

 arate mechanically, and because of the difference in the 



