CHAPTER VI. 



Retention of Cyanamid Nitrogen in Soil. 



The absorption and retention of Cyanamid nitrogen by vari- 

 ous soil constituents has been investigated by only a few 

 workers, and very little has been reported that can be regarded 

 as of practical interest. Such tests to be of value should be 

 made with natural soils, and not with pure constituents, such 

 as ignited glass-sand, as has been done by some investigators. 

 The period permitted for absorption should be at least one or 

 two days, and the proportion of aqueous solvent should not 

 exceed that likely to occur in agricultural practice, nor should 

 larger quantities of nitrogen be applied than are likely to be 

 used by the farmer. 



The retention of nitrogen is doubtless due to physical pro- 

 cesses, as well as to chemical reaction with both the mineral 

 and organic constituents of the soil. (See pp. 39 and 45). 

 Physically, Cyanamid nitrogen is retained in the soil by pro- 

 cesses of absorption in the same way as sodium nitrate, or 

 other salts which do not form insoluble compounds by chem- 

 ical reaction with the soil. By chemical and biological pro- 

 cesses, however, Cyanamid nitrogen is quickly converted to 

 the form of ammonium salts, and these are retained in the 

 soil in the form of humic and zeolitic compounds of ammo- 

 nium. According to A. D. Hall, the weaker the solutions of 

 ammonium salts applied the greater is the percentage of 

 ammonium absorbed by the soil.^ In the field the amount of 

 soil is so enormously in excess that the absorption of ammo- 

 nium salts is practically complete. 



While plants undoubtedly have the power of directly assimi- 

 lating the urea^ that is formed as a transition product during 

 the conversion from cyanamide to ammonium salts, the dura- 

 tion of the urea stage is probably very short in the soil, and 



1 A. D. Hall, The Soil, New York, 1910, p. 215. 



2 Jour. Agr. Sci., Vol. IV, Part 3, p. 282. 



