10 



action of one or more bacteria appears to be proved by an experiment bv 

 Wagner. Two hundred and fifty grammes of fresh horse dung were plac- 

 ed in a flask along with 200 cubic centimetres of carbon disulphide, and 

 the two substances were left in contact for six days. At the end of that 

 time 50 grammes of the mixture were taken out and placed in a flask 

 which was heated in a water-bath at a temperature of 60-65 ° C for 

 four hours All the carbon disulpbide having disappeared at the end of 

 that time, 800 cubic centimetres of a solution of nitrate of soda holding 

 0.4 gramme of nitrogen were poured over the dung. Another sample of 

 dung was dealt with in every respect in the same way, except that it 

 was not treated with carbon disulpbide. In four days it was found that 

 the dung which had not been sterilised with carbon disulpbide had re- 

 duced 56 per cent, of the nitrate, whereas not a trace of denitrification was 

 found to have occurred in the sterilised solution. After the lapse of 

 other three days the whole of the nitrate had been reduced by the un- 

 sterilised dung, while denitrification was just commencing ia the steri- 

 lised material. In fourteen days from the time of placing the nitrate 

 and sterilised dung together 12 per cent, of the nitrate had been reduc- 

 ed, and such reduction amounted to 19 per cent, at the end of twenty- 

 five days. Evidently, therefore, the carbon disulphide had, to start 

 with, cleared the material of active denitrifying organisms, their subse- 

 quent presence being due either to their development from spores that 

 the carbon disulphide had not affected, or to immigration from the 

 atmosphere. 



There is thus no escaping from the conclusion that nitrates, 

 whether naturally present in manure or the soil, or when added 

 in so-called artificial mauure, are rapidly destroyed by organisms 

 which are very abundantion dung, and are also present, though 

 to a much less extent, in soil. Maercker carried out a larjje 

 series of experiments with a number of samples of farmyard 

 manure obtained from the dung heaps of various farms, and found 

 that although certain of the samples proved more denitrifying than 

 others, still the results were, on the whole much the same as those ob- 

 tained with pure faeces. He then proceeded to test the part played bv 

 the straw (wheat) in farmyard manure and found that when this sub- 

 stance was chopped up and applied to the soil it reduced the yield of 

 oats by 89 per cent., and the aggregate yield of three crops of mustard, 

 grown in succession in the same pots, by 74 per cent. The comparative 

 merits of mixtures of urine and dung containing variable quantities of 

 straw were also tested, and it was found that the crop was least, and the 

 loss of nitrogen greatest, in the mixture that contained most straw. 



Wagner's researches into the action of straw (rye) also show that 

 this substance either contains denitrifying organisms in great abundance, 

 or else it induces conditions highly favourable to denitrification. Thus, 

 when a mixture of 300 grammes of dung, 2 grammes of nitrogen in 

 nitrate of soda, and 4 litres of water, was placed in a flask, it took twelve 

 days for complete denitrification to be effected, whereas seven days only 

 were necessary when the mixture received an addition of 100 grammes 

 of straw. In another case 2 grammes of nitrate nitrogen were com- 

 pletely denitrified in twenty-two days in a mixture containing rotten 

 dung, whereas when 100 grammes of straw were added the process was 



