CYANAMID manufacture:, CHEMISTRY AND USES 7I 



when it is converted into nitric acid; so the nitrogen of the 

 lime-nitrogen must be converted into ammonia and nitric 

 acid Before it will yield nitrogen that the plants can assimilate. 

 "5. It is known that the conversion of Cyanamid and the 

 organic forms of nitrogen into ammonia and nitric acid is 

 brought about by the activity of certain soil bacteria and that 

 this conversion, according to the special activity of the soil, 

 sometimes proceeds more rapidly and sometimes more slowly. 

 Upon so-called medium soils in good condition the organic 

 fertilizers as a rule act more completely than upon light dry 

 sandy soils or upon heavy clay soils. The medium loam soils 

 in good condition seem to offer comparatively the best con- 

 ditions for the action of lime nitrogen. Whether the con- 

 version of calcium cyanamide into ammonia proceeds by an 

 intermediate formation of urea is unproved." 



The above was written by Dr. Wagner before the mechanism 

 of the conversion of Cyanamid in the soil had been worked 

 out. These later researches show that the conversion is both 

 physico-chemical and biological, as has been set forth in 

 Chapter V. 



The experiments on the effect of concentration to which 

 Dr. Wagner refers were made in vegetation pots with a 

 variety of nitrogenous compounds, on various types of soil, 

 and with various crops. All the results point to the same 

 general conclusion, which is illustrated in Fig. 5. This test 

 was made with oats planted on a sandy-loam soil, in pots 

 20 cm. high and 20 cm. in diameter. The seed was planted 

 on the day of fertilizing. May 9, 1905, and the grain harvested 

 on July 14, 1905. The lime-nitrogen contained 20.06 per cent, 

 nitrogen, and the calcium nitrate (commercial grade) con- 

 tained 11.65 P^^* cent, nitrogen.^ The yields of grain are 

 plotted against the amounts of nitrogen applied to the soil 

 (Fig. 5)- 



Each of these curves is an illustration of the Law of 

 Diminishing Returns. For the smaller applications of nitro- 

 1 Landw. Vers. Stat., 66, IV-V (1907), p. 346. 

 6 



