6 Subtropical Vegetable-Gardening 



one must either stop growing that crop on that particular 

 soil, or in some way supply the wanting plant-foods. 

 This is accompUshed by using either home-made or com- 

 mercial fertilizers. It must not be thought, however, 

 that plants can use up all the mineral food in the soil. 

 They can take only the soluble minerals, and those that 

 happen to come their way. By resting the land, more of 

 the mineral food becomes soluble. The good effects 

 of fertilizers are due mainly to their being soluble plant- 

 food, and to their being put where the plant can get them. 

 Any substance that will supply the deficient element or 

 elements to the soil, in such a form as to be available to 

 the crop, is considered a fertilizer. It is not uncommon 

 to find an element present in the soil in sufl&cient quantity, 

 but in such form that the crop cannot make use of it; 

 in other words, the element is not available. 



COMPLETE FERTILIZER 



A fertilizer that contains all three elements, nitrogen 

 (as organic nitrogen, nitrate, or ammonia), phosphorus (as 

 phosphoric acid), and potassium (as potash), is said to 

 be complete. The amounts of the elements vary with the 

 different brands of fertilizer, and should be suited to dif- 

 ferent crops and the different soils for which they are to 

 be used. The amount of an element in a special fertilizer 

 is governed largely by the amount of that element removed 

 from the soil by any particular crop. 



An incomplete fertilizer is one which is wanting in any 

 one or more of the three fertilizing elements. These are 

 known either by their chemical name, as acid phosphate. 



