CHAPTER II 

 FERTILIZERS 



Thikteen of the eighty and more elements now recog- 

 nized by chemists are more or less directly concerned in 

 the growth of agricultural plants. 



Of the thirteen elements, silicon, chlorin, and sodium are 

 perhaps not essential, and are nearly always abundant 

 enough. Oxygen and hydrogen are the elements of 

 water. Carbon is derived directly from the air. Sulfur, 

 calcium, magnesium, and iron are contained in most 

 soils in fair amounts. Only nitrogen, phosphorus, and 

 potassium often become scarce, and the plant must have 

 these three. They play such an important part in the 

 plant economy, and are present in such varying quanti- 

 ties, and so often one or more of them is insufficient in 

 amount, that one looks upon them as the essential ele- 

 ments ; though they are not more necessary to the plant's 

 welfare than some other elements. A deficiency of any 

 one will cause the plants to look sickly, and make 

 them fit subjects for insect and fungous attacks, to which 

 they then readily succumb. If a field has been producing 

 good crops for a number of years and then gradually 

 fails without visible cause, it is a fair indication that 

 some form of food for that crop is becoming exhausted, and 



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