No. 6. DEPARTMENT OF AGRICULTURE. 343 



soil may at first check or suspend nitrification until the said lime 

 lias been converted into carbonate. This, however, takes place rapid- 

 ly, diminishing in turn its strong alkaline properties and permitting 

 nitrification to commence more actively than before. 



Equally unfavorable to nitrification is an acid condition of the soil. 

 The extreme susceptibility of the nitrifying organism to acid is 

 shown by the researches of Wiley and Ewell.''^ In the experiments 

 of the latter, solutions containing calcium chloride and w'ater were 

 seeded with soil, containing of course nitrifying bacteria. In this 

 medium nitrification continued until the medium reached an acidity 

 equivalent to 4 c. c. of normal acid per 100. 



It is a well known fact that nitrification has practically ceased 

 in forest and woodland soils. The same is true, but to a lesser de- 

 gree, in the soil of old pastures. That such cessation of nitrification 

 is not due to the absence of nitrifying bacteria is shown by the fact 

 that such soils begin to nitrify rapidly upon the addition of some base 

 which overcomes the acidity. 



In the experiment of Dumont and Crochetelle, already referred to, 

 a soil which had been in grass from time immemorial and contained 

 6.84 per cent, of humus w'as treated with variable amounts of car- 

 bonate of potash. It w^as stirred and watered several times dur- 

 ing the experiment. After one month the nitrates were extracted 

 with the following results: Nitric nitrogen, per 1000 grams of soil, 

 without addition of carbonate of potash, 70 mg; with 1 gram of 

 carbonate of potash per 1000 grams of soil, 160 mg; with 2 grams of 

 carbonate of potash, 230 grams; with 3 grams, 250 mg; with 4 

 grams, 130 mg; with 5 grams, 73 mg. 



In an experiment with marsh land containing 5.76 per cent, of 

 humus similar results were obtained, showing that while in the 

 original soil nitrification was practically nil, the addition of car- 

 bonate of potash resulted in active nitrification. 



Too great a degree of alkalinity, as has been already seen retards 

 or entirely checks nitrification. 



In a too concentrated solution of urine, the nitrifying process is 

 hindered after a certain time by the accumulation of ammonium 

 carbonate which is being produced by the ammonifying bacteria at a 

 more rapid rate than the oxidation of the ammonia to nitric acid. 

 This is the condition of most stable manures in bulk or before they 

 become intimately mixed through the soil. 



The addition of lime to stable manure in a state of ammoniacal 

 fermentation would only still further hinder their nitrification by 

 increasing alkalinity, and would also drive oflf much valuable am- 

 monia. Lime added to fresh manure before ammonium carbonate 

 has been produced will not cause the above loss of free ammonia, 



