vii.] DENITRIFICATION 229 



less nitrogen than that given by the unmanured plot. 

 Where straw was used with nitrate of soda the two 

 gave a crop containing 23 lbs. less nitrogen per acre 

 than the nitrate alone ; where urine was used alone, 

 the produce contained 25 lbs. more nitrogen per acre 

 than when it was used in conjunction with cow-dung 

 and straw. 



In fine, all the results pointed to the same con- 

 clusion that large amounts of fresh organic manure 

 not only do not themselves help the crops, but 

 diminish the effect of other rapidly acting nitrogenous 

 manures like nitrate of soda, sulphate of ammonia, or 

 urine. 



The action cannot, in the two latter cases at least, 

 be put down to denitrification proper, unless it is 

 supposed that nitrification and subsequent denitrifica- 

 tion can proceed practically simultaneously in the 

 same soil. It must either be attributed to the fact 

 that nitrification is very much checked by the 

 presence of large amounts of organic matter ; or to 

 the conversion of readily available nitrogen into a 

 comparatively insoluble albuminoid form in the actual 

 material of the enormous numbers of bacteria that 

 are developed by the free food supply ; or, lastly, 

 to those fermentation changes of organic nitrogen com- 

 pounds which result in the liberation of free nitrogen. 

 Several of these changes may take place together ; the 

 essential point is, that nitrification does not go forward 

 in the presence of much organic matter, which instead 

 favours all the bacterial processes resulting in the 

 development of free nitrogen. 



The conditions indeed which prevailed in these 

 experiments are scarcely comparable with the ordinary 

 practices of agriculture. Enormous quantities of fresh 

 organic manure were employed immediately before the 



