12 



Evidently, therefore, the denitrifying power of the dung is lost to a 

 large extent by contact with the soil for two or three months. 



Wagner carried out a series of experiments which also go to show 

 that the denitrifying bacteria are much less energetic in old than in new 

 dung. The system which he adopted was as follows: — A number of 

 cemented pits of a capacity of one cubic metre (about 35 cubic feet) 

 were prepared, and into each of these 500 kg. (about half ton) of fresh 

 horse dung was placed. From these pits samples of dung were drawn 

 every fourteen days, and the denitrifying influence of the dung was 

 tested by placing 300 grammes in a flask along with 4 litres 

 of water and 100 centimetres of a solution of nitrate of soda that 

 contained two grammes of nitrogen. These flasks with their con- 

 tents were placed in a room at a temperature of 50 to 57 ° Fahr., and 

 were daily tested with diphenylamin, so that the time could be accurately 

 determined when the whole of the nitrate of soda had been denitrified. 

 In one series of pits the dung was turned over every seven days, and in 

 another series it was turned once a fortnight, but so far as denitrification 

 is concerned no difference whatever could be detected between these two 

 systems. Confining our attention, therefore, to one series only — that 

 where turning was done every fortnight — we find that the sample re- 

 moved at the end of fourteen days took thirteen days to denitrify the ni- 

 trate solution, that removed at the end of a month took nineteen days, 

 that removed at the end of six weeks took thirty-one days and that 

 removed at the end of two months took forty-one days, while that re- 

 moved at the end of ten weeks took sixty-five days. Or, looked at from 

 another point of view, it was lound that whereas dung fourteen days 

 old completely denitrified the nitrate of soda in thirteen days, denitrifi- 

 cation had only proceeded about halfway in the same time in the case of 

 the six-weeks-old dung. Wagner points out that the superior action of 

 well-rotted farmyard manure is probably in large part due to its not 

 destroying the natural nitrates of the soil to anything like the same 

 extent as occurs in the case of an application of fresh manure. This 

 point was demonstrated by Wagner in pot experiments with oats. Ni- 

 trate of soda alone produced an average yield of 244.3 grammes, while 

 the yield when equal quantities of nitrogen were added, in the one case 

 in the form of fresh horse-dung, and in the other case in the form of 

 rotton or " humified" (to Anglicise the word " humifizierter") dung, 

 was 177.0 and 243.3 grammes respectively. This variation in the 

 action of the two samples of dung of different ages was also emphasised 

 when they were added to soil which had been manured with 2 grammes 

 of nitrogen derived from cow-urine. With this substance alone the 

 yield was 216.7 grammes, while it was 146.1 grammes when the urine 

 was supplemented by fresh dung and 223.5 grammes when rotten dung 

 was used. 



Wagner and Maercker have been occupied with, and are still en- 

 gaged upon, an extensive series of experiments into the conservation of 

 the nitrogen and organic matter of farmyard manure, and the results so 

 far obtained are of the highest interest and value. Space does not, how- 

 ever, permit of our reviewing those results ; but it may be pointed out 

 that, although great loss of nitrogen, combined and in the elementary 

 form takes pla3e in the dung-heaps, the loss is almost entirely confined 

 to the nitrogen of the urea ; the albuminoid nitrogen of the solid faeces 



