VII.] 



DEN1TR1FICA TION 



199 



organic matter, will obtain the oxygen, which they 

 normally require for the breaking up of the organic 

 matter, at the expense of the nitrate. 



Many experiments, in which farmyard and other 

 organic manures have been employed in conjunction 

 with nitrate of soda and similar active compounds of 

 nitrogen, have shown a smaller crop for the manures 

 used together than when either was employed singly. 

 These results were particularly apparent when large 

 quantities of material like fresh horse-dung or chopped 

 straw were used in pot experiments. With well-rotted 

 dung, the effect of organic material in depressing the 

 yield which should be given by the nitrate was not 

 so great. 



The nature of the results obtained may be seen 

 from the following table, which gives the percentage 

 recovered in the crop of the nitrogen supplied in the 

 manure, when used alone, or in conjunction with fresh 

 horse-dung : — 



Percentage of Nitrogen Recovered (Wagner). 



Numbers of similar experiments in pots have been 

 recorded. In some cases the use of fresh dung has 

 even resulted in a smaller crop than was obtained with- 

 out any manure at all ; but it should be noted that 

 very large amounts of the organic manures were used, 



