FERTILIZERS 47 



Again, if phosphoric acid was not needed for a 

 particular soil and crop, it would then have no agri- 

 cultural value in that case, but would still have a 

 market, or commercial value. 



In the selection of a fertilizer, the agricultural 

 value should be considered first and the commercial 

 value second. Good results are of first importance 

 and depends on the agricultural value. 



THE USE OF FERTILIZERS. 



68. In order to use fertilizers intelligently, it is 

 necessary to know the specific action of the three 

 plant foods; nitrogen, phosphoric acid, and potash, 

 their sources, and when and how to apply them. 

 The few experiments which have been made with 

 various fertilizers on citrus trees confirm the same 

 general principles that hold with reference to other 

 crops. They will be briefly stated. 



EFFECT OF NITROGEN. 



69. The presence of available nitrogen is shown 

 by a dark, healthy, green color of leaves and stems. 

 Growth is vigorous. The feeding power of the plant 

 is increased. If an excess of nitrogen is available at 

 the time of flowering, and the supply of phosphoric 

 acid insufficient, the bud and bloom and fruit will be 

 imperfect and the total amount of fruit lessened. 

 The fruit will then be rough and thick-skinned. 

 Constant use of stable manure, without the addition 

 of phosphoric acid, will produce thick-rind fruit. 

 The size of fruit may be increased by nitrogen. A 



