68 NITRIFICATION AND DENITRIFICATION. 
may furnish this needed carbon, and the cellulose present in hay 
or straw will also furnish it. Any form of decaying matter that 
contains great amounts of hay or stubble is especially subject 
to denitrification. Horse manure, containing as it does large 
amounts of hay, shows greater losses of nitrogen than the manure 
of cattle, which contains less carbonaceous material. 
The extent of the actual losses caused by these denitrifiers in 
ordinary farm processes is not fully known. It is certain that in 
concentrated decomposing solutions the action is vigorous, but 
it is not so great in less concentrated masses. In the manure heap 
there is always some loss in this way, and when great quantities 
of manure are spread over a plot of cultivated ground, denitrifica- 
tion doubtless causes considerable loss. When, however, the manure 
is applied in limited quantity, so that it is mixed with a considerable 
amount of soil, the evidence seems to show that the losses are slight 
if any. In ordinary soil, therefore, denitrification is not a phenome- 
non of much significance. In concentrated manures, however, 
especially if they contain much hay, it may be great. One very 
impoitant lesson is to be drawn from these facts. Nitrates should 
never be mixed with manure. The nitrates will simply be thrown 
away, since the denitrification in the manure heap will surely 
reduce most of the nitrate to free nitrogen, thus causing its complete 
loss. Further, the denitrification is greatest in fresh, concentrated 
manure, while it diminishes greatly in manure after it has partly 
decayed. The denitrifiers do not find the partly decomposed 
organic substance favorable to their life, and do not flourish. Hence, 
the use of large amounts of partly rotted manure upon a soil is 
possible without bringing about a nitrogenous loss, while the use 
of the same amount of fresh manure would be undesirable. 
