SECTION II. THE INCREASE OF CROPS BY 

 THE USE OF FERTILIZERS 



Crop Stimulation and Nitrogen. Any substance added to 

 the soil which produces an increase in the crop may be called 

 a fertilizer, but an increase in the crop produced by any 

 physical or mechanical means which improve soil condition 

 is not considered a fertilizer. A garden spade unquestionably 

 increases crop production, but it is not called a fertilizer. 

 In the same way, the addition of sand to clay or clay to sand 

 will increase crop production, but neither clay nor sand are 

 considered to be fertilizers. It is necessary to restrict the 

 term fertilizer to substances having a specific action on plants, 

 followed by an increase in growth. 



Nitrogen, phosphorus and potassium are the chief 

 elements having a specific fertilizing effect. The most 

 important compounds of nitrogen that occur in fertilizers 

 are nitric acid, ammonia, amides and albuminoids. Of these 

 the nitrates are very fully oxidized compounds, and are 

 produced in the soil from ammonia by bacterial action and 

 oxidation. Similarly, ammonia is obtained from amides, 

 amino acids and other simple organic compounds containing 

 nitrogen. These, in their turn, are obtained from albuminoids 

 which have been decomposed by bacteria and larger forms of 

 life. 



The Result of the Application of Nitrogen. Appli- 

 cations of soluble nitrogenous manure are speedily indicated 

 by the deepening green colour of the crop, by greater develop- 

 ment of leaf and increased growth of stem. Judged from its 

 most obvious visible results, the main function of nitrogen 

 seems to be an increased production of leaf and stem. The 

 deficiency of available nitrogen in a soil is at once shown in 

 the stunted growth of stem and the yellow tint of leaf. 



