318 SOILS AND MANURES 



only take place in the presence of air. Free nitrogen 

 may possibly be produced in both ways, but in farmyard 

 manure the conditions are not generally favourable to the 

 nitric fermentation (p. 157). It is evident that whatever 

 the cause, the nitrogen liberated in the free state is lost 

 beyond all hope of recovery. 



A more potent cause of the disappearance of ammonium 

 compounds under ordinary circumstances, is their re- 

 conversion into protein compounds by the action of cer- 

 tain bacteria which can utilise the nitrogen for the for- 

 mation of the albuminoids of which they are partly 

 composed. This change, it will be seen, is exactly the 

 reverse of those previously described. It results in the 

 conversion of the soluble nitrogenous matter into in- 

 soluble forms. It tends to conserve the nitrogen, but 

 reduces its manurial activity. The two kinds of change 

 probably occur simultaneously, and the amount of solu- 

 ble nitrogenous matter present at any time, depends upon 

 the relative rates at which they take place. The forma- 

 tion of ammonium carbonate takes place at first very 

 rapidly but afterwards becomes slower and is gradually 

 overtaken by the reverse change. 



The soluble nitrogenous matter is also liable to direct 

 loss by volatilisation of ammonia and by solution in 

 water which drains from the heap. 



Loss IN MAKING AND STORING. 



The loss of fertilising ingredients which farmyard 

 manure suffers during the process of making .and storing, 

 arise principally from the causes mentioned above, viz., 

 the evolution of free nitrogen gas, volatilisation of am- 

 monia and the drainage of water. In actual practice 

 the losses cannot be altogether prevented, but they can 

 be minimised by careful management. 



