CHAPTER X 



THE RELATION TO NITROGEN 



THE significance of the nitrogen content of soils has been 

 recognized deservedly as so important in crop production 

 that a stupendous number of investigations has been 

 directed toward securing the facts regarding the diverse 

 relations of this nutrient. Many of these investigations 

 have yielded data of surprising interest respecting the use 

 of nitrogen by higher plants and by microorganisms as 

 well. Furthermore, the results have been sufficient to 

 demonstrate most clearly the intimate relations existing 

 between soil bacteria and cultivated crops as regards the 

 nitrogen supply. With phosphoric acid and potash it 

 constitutes the trio of nutrients which experience has de- 

 manded as usually the most important fertilizers for crop 

 production. 



118. Combined nitrogen.- -The water-culture experi- 

 ments (sections 78-80) have demonstrated in a manner 

 sufficiently convincing that the nutrient solutions for 

 higher plants must contain nitrogen. As soon as the 

 supply of this element in the seed is fairly exhausted the 

 addition of combined nitrogen is required. About the 

 middle of the last century Boussingault showed conclu- 

 sively that the N 2 of the air, unlike the CO 2 , is not directly 

 serviceable as a source from which nitrogenous foods 



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