REACTION OF MEDIA 219 



experiments, Kochenavski demonstrated that potassium carbo- 

 nate is more efficient in this regard than is calcium carbonate, 

 probably because the potassium acts as a food in addition to the 

 neutralizing of the acid. Owen has found magnesium carbonate 

 even more efficient than potassium carbonate, and this is in keep- 

 ing with the findings of Lyon, and Bizzell and White. Pangan- 

 iban's findings appear to differ from these, for he claims that liming 

 greatly increases nitrification only when the limestone contains little 

 magnesium carbonate. The soil of the Utah Greenville farms con- 

 tains 16.88 per cent, of lime (CaO) and 6.1 per cent, magnesium 

 (MgO), and they nitrify ammonium sulphate, dried blood, and 

 cottonseed meal readily. 



The carbonates are not the only substances in the soil which 

 serve as bases for nitrification, since, according to Ashby, a marked 

 nitrification of ammonium salt can be brought about in the presence 

 of ferric hydrate, either in the freshly precipitated state or as 

 "iron rust." In solutions, however, nitrification is not completed 

 where iron is the only base, probably because the ferric nitrite or 

 nitrate formed dissociates and the solution becomes acid. 



The double ammonium combination formed by the absorption 

 of ammonium salts by modelling clay can most probably be nitri- 

 fied in the absence of any base, but the corresponding combination 

 with peat undergoes no nitrification in the absence of a base. 



One of the functions of the base in nitrification is to form ammo- 

 nium carbonate, and the facility with which nitrification is set up 

 by different carbonates depends upon the rapidity with which 

 they can react with a neutral ammonium salt to produce ammo- 

 nium carbonate. This reaction is greater with magnesium car- 

 bonate than with calcium carbonate, but is almost absent with 

 copper carbonate. 



The quantity of lime which must be added to a soil for maximum 

 nitrification varies with the original reaction of the soil and the 

 fertilizer to be nitrified; ammonium sulphate requires more than 

 bone meal, cottonseed meal, or dried blood. 



There should always be an excess of the base present, for Fischer 

 found that the theoretical amount of lime (200 grams of calcium 

 carbonate) required for the nitrification of ammonium sulphate 

 (132.7 grams) was not sufficient for complete nitrification, but 

 about three and one-half times the theoretical amount was required. 

 Even much larger quantities of either magnesium carbonate or 

 calcium carbonate may be used without ill effect, but large quan- 

 tities of quicklime may cause a rapid burning out of the organic 

 matter and even volatilization of ammonia and may even stop 

 nitrification. For, while nitrification takes place in a feebly alka- 

 line medium, yet the presence of anything beyond a small quan- 

 tity of an alkaline salt is a hindrance to the process, and a large 



