2 Fertilizers 



upon the observance of which their success depended. 

 One of the first needs, therefore, in the use of commercial 

 fertilizers is a more or less definite knowledge of what 

 constitutes fertility, and of the principles which under- 

 lie crop production. 



SOIL FERTILITY 



The full meaning of the term "soil fertility" is not 

 easily expressed, since many conditions are involved, 

 all of which exert more or less influence. The po- 

 tential fertility, which is measured by the total content 

 of the food elements contained in a soil, is made prac- 

 ticable, or usable, in proportion as the conditions are 

 favorable. The more important of these influencing 

 conditions are here briefly discussed. In the first place, 

 it is of the utmost importance that a soil should contain 

 those elements found in the plant; hence, it is almost 

 self-evident that a fertile soil must contain a maximum 

 quantity of those particular elements or constituents 

 which are removed from the land in maximum amounts 

 by the crops grown. The removal of crops rapidly ex- 

 hausts the soil of these elements, and finally reduces the 

 quantity contained in the soil to so low a point as to make 

 profitable cropping impossible. 



Chemical elements needed in plant growth. 



Careful studies and experiments have shown that 

 plants actually take from the soil at least ten chemical 

 elements which are required for their normal growth and 

 development: viz., nitrogen, potassium, phosphorus, 

 magnesium, sulfur, sodium, iron, chlorin, silicon and 

 calcium. Besides these elements, others are often found, 

 including manganese. It is not to be inferred that all 



