IV. THE EEACTIONS OCCUEEING IN SOILS 65 



(e) Absence of strong light. Bright light, e.g., sunlight, suspends 

 the action of and eventually destroys the organisms. 



(/) Presence of sufficient oxygen. Since the process is one of 

 oxidation it is obvious that free supplies of oxygen should be provided. 

 Hence it cannot proceed in a waterlogged soil and is greatly increased 

 by stirring the soil. 1 



(g) While the work of the nitrous organism obviously proceeds- 

 best in the presence of considerable amounts of ammonium salts, 

 the nitric organism is rendered inactive by more than small amounts- 

 of such compounds and only produces nitrates when the ammonium 

 compounds have, to a great extent, been destroyed by the nitrous or- 

 ganism. Nitrification is stopped if the amount of ammonium car- 

 bonate present exceeds 400 parts of nitrogen per million, but 1000 

 parts of nitrogen as ammonium chloride do not prevent the action* 

 Warington 2 found that the presence of gypsum effectively prevented 

 the inhibitory effect of too large a quantity of ammonium carbonate by 

 producing ammonium sulphate. The presence of gypsum would thus 

 be advantageous in all cases where rapidly decomposing animal nitro- 

 genous matter (e.g., urea) has to be nitrified, for it would prevent the 

 danger of the too rapid formation of ammonium carbonate, and con- 

 sequent stoppage of nitrification (or even in some cases the destruction 

 of the nitrifying organism). 



(h) The action of the nitric organism is hindered by the presence 

 of alkalies (sodium carbonate) or by calcium chloride, but is favoured 

 by bicarbonates and sulphates. 



(i) Nitrification can be stopped by the use of certain antiseptics, e.g., 

 chloroform or carbon disulphide vapour. It has even been suggested 

 to employ the latter in autumn to lessen loss of nitrates by drainage 

 from a soil. 3 



(k) Potash compounds added to soils rich in humus have a favour- 

 ing action upon nitrification, especially if the carbonate be employed, 

 or if calcium carbonate be simultaneously applied. 4 Some of the 

 results obtained are given below : 



Moor soil Soil +4 -5 Soil + 2-5 Soil + 5 Soil + 2 -5 per cent CaCO^ 

 only. per cent per cent per cent +5 per cent K 2 S0 4 . 



K a CO a . CaC0 3 . K 2 S0 4 . 

 Amount of nitric 1 , 

 nitrogen pro- 

 duced in 20 i 25 438 30 18 to 25 189 

 days, per mil- 1 

 lion. 



With reference to the distribution of the nitrifying organisms, 

 Warington found that they did not exist at greater depths than 18 

 inches and were most abundant within a short distance from the 

 surface. In later experiments he found that a few nitrifying organisms 

 were present even at a depth of several feet. 



1 Deherain, Compt. Bend., 116, 1091. 



2 Jour. Chem. Soc., 1885, Trans., 758. 



3 Deherain, Ann. Agron., 1895, 501 ; Jour. Chem. Soc., 1896, Abstracts, ii. 329. 



4 Dumont and Crochotelle, Compt. Rend., 118, 604; Jour. Chem. Soc., 

 1894, Abstracts, ii. 248. 



5 



