CHAPTER III 



CHEMICAL FERTILIZERS; AND LIME 



A fertilizer is a material added to the soil for the purpose of supply- 

 ing food for plants. 



An amendment is a substance or material that modifies the physical, 

 mechanical and chemical nature of the soil. 



Stable manure is both fertilizer and amendment. Lime is used 

 mostly as an amendment, since it is not often necessary to supply it for 

 the plant-food that it contains. On sandy soils it may be needed as 

 a fertilizer. 



The extent of the fertilizer industry is indicated by the following 

 figures of complete fertilizers manufactured in the United States in 

 two given years : 



Fertilizer discussions are concerned mostly with nitrogen, phosphorus, 

 and potassium (always in combination with other elements, never used 

 in their elemental form), since these are the elements most likely to be 

 deficient in the soil. To be economically usable as a fertilizer, a 

 material must not only contain some one or more of these three 

 elements in available form, but it must be relatively low in price and 

 obtainable in large quantities. Nitrate of potash (saltpetre) is a good 

 fertilizer, but it is impossible to use it because of the cost. Many of 

 the fertilizer materials, as bone-black, blood, ashes, are waste 

 products or by-products. 



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