5 



It is clear from the work of Winogradsky that free nitric acid ia 

 not produced at any stage of the process, but that two stages of oxi- 

 dation take place, (1) oxidation of ammonia to an alkaline nitrite, (2) 

 complete oxidation of the nitrite to nitrate. 



Unless oxygen (air), chalk, carbonic acid gas and a trace of such 

 mineral foods as phosphates and potash be present, the necessary raw 

 materials for nitrification are lacking and its progress imp )ssible. It 

 is certainly true that a salifiable base such as chalk is necessary for 

 nitrification but it is a gross misrepresentation to state that this ne- 

 cessity lies in a need for the neutralisation of free nitric acid, which 

 is perhaps the most corrosive substance that could be brought into 

 contact with living organisms. 



Conditions affecting the Nitrification of Ammonia. 



A. — Presence of organisms. 



Fortunately for the agriculturist, the bacteria responsible for nitri- 

 fication are universally distributed nnd no practical cultivator runs risk 

 of loss through the actual absence of nitrifying organisms. Cultivated 

 soils from all sources, desert sand and rocky fragments from lofty 

 mountain tops have all yielded proof of the presence of nitrifying bac- 

 teria Warington found that all the samples taken from the cultivated 

 surface of the soil which he tested contained nitrifying organisms. 

 At a depth of two feet, powers of nitrification were occasionally lack- 

 ing, while at a depth of six feet and over the soil had lost all such 

 powers. Nitrifying organisms, therefore, are mainly present in the 

 'upper tilled surface of the soil and do not exist in the lower depths of 

 unstirred soil. Such a distribution is obviously due to the fact that 

 conditions favourable for nitrification are alone possible in the upper 

 surface of the soil. 

 B.—Air. 



The atmosphere contains one fifth of its volume of oxygen gas and 

 as this latter material is requisite for the purpose of oxidising ammo- 

 nia, a full supply of air is necessary for the free progress of the change. 

 Drainage, cultivation with plough and harrow, spade, fork and 

 hoe are time-honoured tributes to this fundemental requirement of 

 cultivated ground A water-logged soil in which the pore^ are satu- 

 rated with water is an impossible medium for nitrification owing to 

 the absence of air. The wonderful improvements that have been 

 brought about in the case of stiff, impervious soils by drainage and 

 good cultivation are closely associated with the improved aeration of 

 the soil and the consequent promotion of nitrification. 



C. — Presence of salifiable base. 

 Chalk. It is desirable that special emphasis be laid on the absolute 

 necessity of such an alkaline carbonate as chalk for the general re- 

 quirements of the process of nitrification Those traditions of good 

 cultivation which have been evolved through centuries of experience 

 and observation by generations of practical men, have received marked 

 confirmation and a rational explanation through the latest discoveries 

 as to the causes and conditions of nitrification. The recommendations 

 of science, based upon a cnmprehension of the causes at work, are sin- 

 gularly in harmony with the general maxims of good cultivation, based 

 upon a shrewd appreciation of obvious effects. Of all the conditions 



