THE FERMENTATIONS OF MANURE. 75 



then brought about by the nitrous bacteria which are not prevented 

 from growing by the presence of free ammonia. The nitric bacteria 

 are, however, so extremely sensitive to ammonia that they cannot 

 begin the formation of nitric acid till ammonia gas has entirely 

 disappeared and therefore probably not until decomposition has 

 ceased. When the nitrifying processes do begin, they complete the 

 ripening of the manure. They oxidize the nitrogen compounds 

 which are left, the ammonia salts becoming first changed to nitrites 

 and then to nitrates. As this process continues the manure is 

 more and more filled with nitrates and therefore becomes a better 

 and better food for plants. At last when the process is ended and 

 the manure is fully ripened, enough of nitrogen is converted into 

 nitrates to furnish a most valuable supply of food for vegetation. 



Fresh and Ripened Manure. The transformations which 

 we have considered constitute what is called the ripening, rotting, 

 or composting of manure. They are clearly similar to those changes 

 already considered as taking place in the transformations in the 

 humus, but rendered more intense by the concentration of the 

 manure heap. It is evident that manure is of no value to plants 

 until it has undergone these transformations, and equally evident 

 that the transformations may, and some of them do, go on in the 

 soil after the manure is mixed with it as well as in the manure heap. 

 Indeed, they will probably go on better in the soil, and in some 

 important respects it is an advantage to incorporate the manure 

 with the soil while fresh rather than to wait for it to ripen. We have 

 noticed that the loss from decomposition and denitrification is 

 slight when these processes occur in the soil, while they are con- 

 siderably higher when the ripening occurs in the concentrated 

 manure heap. The loss is especially large from the liquid manure 

 in warm weather, which, if kept in tanks or allowed to accumulate 

 with the manure pile, will undergo a very rapid ammoniacal 

 fermentation resulting in large losses of nitrogen. If, however, 

 it is mixed at once with the soil the ammonia is fixed as fast as formed 

 by the soil ingredients, is soon nitrified, and the loss is largely 

 prevented. There has thus come to be recommended the practice 

 of spreading the manure upon the soil as quickly as convenient, 



