vil] LOSSES OF SOIL NITROGEN 201 



presence of large amounts of organic matter; or tc 

 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 prevail in these experi- 

 ments are scarcely comparable with the ordinary practices 

 of agriculture. Enormous quantities of fresh organic 

 manure are employed immediately before the crop is 

 sown, the temperature of the pots, or of the ground in 

 the field experiment quoted, is very high, so that it 

 is easy to see that an abnormal condition, both as 

 regards nitrification and the supply of oxygen and water, 

 must be developed. 



There are not lacking both long-continued experi- 

 ments and ordinary farming experience to show that 

 nitrates and other artificial manures can be used in 

 conjunction with dung with the best effects. 



For example, the mangold crop at Rothamsted 

 shows the following average results for the recovery of 

 nitrogen from various nitrogenous manures used first 

 with mineral manures alone and then with annual 

 dressings of 14 tons per acre of farmyard manure, a 

 quantity that never would be employed so frequently 

 in practice: — 



[Table, 



