26 



in is most true, but then the conditions producing dentrification will 

 have diminished, or entirely ceased. That nitrification and denitrification 

 can occur simultaneously in the same place has yet to be proved, (i) till 

 this is donewe must assume that nitrification is considerably retarded by 

 the addition to the soil of large quantities of fermentable organic matter. 



It is only right to add that the simultaneous occurence of nitrifica- 

 tion and denitrification is not accepted by all the German investigators 

 as a sufficient explanation of the diminished return from ammonium 

 salts, urine, etc., when these manures are mixed with dung. Pfeiffer 

 believes that an evolution of nitrogen from ammonia, due to its partial 

 oxidation, takes place in the soil under the circumstances in question ; 

 and that the considerable loss of nitrogen which occurs in an aerated 

 dung heap is due to the same action, which he assumes to be brought 

 about by bacteria. This view is at present little more than a supposition, 

 but it indicates that the explanation first mentioned is by no means re- 

 garded as satisfactory. 



When considering the action of large applications of organic man" 

 ure, both in retarding nitrification and in setting up denitrification, we 

 must of course bear in mind that all kinds of organic matter have not an 

 equal effect, and that mere quantity will not alone determine the result. 

 When, instead of fresh horse dung, Wagner used black, humified 

 manure, which have been frequently turned over during four months, 

 the injurious effect on the action of nitrate of sodium almost disappear- 

 ed. The return from 100 of nitrogen in nitrate of sodium was now 73, 

 and from 100 of nitrogen in cattle urine 63, (2) instead of 52 and 40, 

 respectively, when fresh horse dung was employed. Maerckor also ob- 

 served that if horse dung was applied to the soil two months before the 

 nitrate of sodium, its denitrifying action was scarcely perceivea. Thi* 



(1) In some of the recent German analyses of farmyard manure consider- 

 able quantities of nitrates are mentioned. In a small experimental mass it 

 may happen that the conditions suitable for nitrification may in the course of 

 time occur, but an ordinary dung heap seems the most unlikely situation tor 

 the nitrifying process. The mode of determining the nitrates is not always 

 mentioned, but, in one paper, boiling the extract of the manure with aluminum 

 and soda is stated to be the method employed ; this must give far too high re- 

 sults, Schloesing's method of estimation as nitrate oxide gas would give 

 accurate results. Reduction to ammonia with a copper- zinc couple, and dis- 

 tillation with magnesia, would also give fair results. 



(2) A hasty reader of Wagner's paper would come to the conclusion that 

 the return of nitrogen in the crop was in this instance 39 and 34 per cent, re • 

 spectively, these being the numbers printed in the table ; they are obtained by 

 dividing the nitrogen in the increase by the total nitrogen applied to the pot. 

 This mode of reckoning fails, however, to show the return yielded by the 

 nitrate of sodium or urine, wl 'eh is the point in question. To gh > one example: 

 2 grams of nitrogen in the form of humified horse dung gave an increase of 

 "097 gram of nitrogen in the crop : 2 grams of nitrogen as humified horse 

 dung, plus 2 grams in the form of nitrate of sodium, gave an increase in crop 

 of 1*548 gram of nitrogen. The return from 2 grams of nitrogen as 

 nitrate of sodium was thus 1'548— '097— 1*451 gram or 72 55 per cent. The 

 ill-effects of mixture with dung are much exaggerated by the mode of calcula- 

 tion adopted in Wagner's tables ; in his text, however, the true proportions 

 will usually be found. 



