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, 
