400 



Artificial Farmyard Manure. 



slightly alkaline. Hence the supply of nitrogen in the 

 ammonium sulphate alone fails to lead to definite breakdown 

 since the medium .soon becomes markedly acid, while, on the 

 other hand, the supply of an alkaline compound alone, such as 

 caustic soda, is equally ineffective, since a source of nitrogv^n 

 is lacking. The addition of nitrogen in the form of urine, urea, 

 ammonium carbonate, or peptone within certain concentrations 

 immediately sets in train rapid decomposition changes, and 

 results within the period of a few weeks in the production of 

 dark-coloured, well-disintegrated, structureless material closely 

 resembling well-rotted manure. That ibis should be the case 

 with urine was perhaps not remarkable, although the factors 

 which operate in the essential dung-making process had not 

 then been individually worked out, but that an essentially 

 characteristic product could be obtained without the use of 

 urine or of the faecal portion of the manure as ordinarily pro- 

 duced was at once suggestive. On the basis of subsequent 

 work, it may indeed be claimed that, in the production ofi 

 normally well-rotted farmyard manure, the mass inoculation of 

 the litter with the large bacterial population of the fieces does 

 not exert an}^ marked contributory influence on breakdown 

 changes: that the urine, as such, apart from being the carrier 

 of nitrogen, does not induce any characteristic changes in the 

 straw, while the typical siriell and colour of stale urine from the 

 manure heap may be successfully reproduced from straw treated 

 with ammonium salts. 



Although it is important that available nitrogen should be 

 present for the rotting process, it is also not less essential that 

 the quantity of nitrogen should not exceed a definite amount 

 both actually as well as in concentration. In other words, if the 

 concentration of ammonium carbonate produced from the de- 

 composition of urine or urea exceeds a definite limit, not only 

 are straw-breakdown changes definitely held up. but they 

 continue to be inoperative until by volatilisation, and con- 

 sequently loss of nitrogen to the air, the concentration or 

 alkalinity has been reduced to the upper limit of growth of 

 n:^ro-organisms. This must he regarded r/s particularlii 

 hnpoiianf, since the highest concentration for rapid hreahdou n 

 is apprcciahJjj below that of the ireahest vndUiitcd urine. 



It follows that it is quite impossible to produce well-rotted 

 dung by the use of neat urine without considerable losses. This 

 fact mav be illustrated by the following table, and, incidentally, 

 is shown by all the investigations that have bc^n c.iri'ied out 



