22 
The Colorado Experiment Station. 
the farmer who applies from ten to twenty tons of well rotted . 
manure per acre and who keeps his land well cultivated, need feel 
little concern from losses on this account. It is true, however, in 
truck gardens and greenhouses, where the ground is pretty well 
saturated, and where an abundance of organic material is used, a 
temporary loss of nitrates is sometimes experienced. 
Those who have held that soil may suffer a loss of nitrates 
following the application of fresh manurs, if such is the fact, have 
explained the phenomenon by saying that vast numbers of denitrify¬ 
ing bacteria, which do the damage, are introduced with the manure. 
While the bacterial content of the soil is unquestionably increased 
by this addition, the reduction is probably due to an entirely dif¬ 
ferent cause. The large amount of organic matter in the manure 
appears to be immediately responsible for the trouble by furnishing 
abundant food for the denitrifying organisms already in the soil. 
A mere increase in numbers would have little to do with stimulating 
activity, and furthermore, ordinary soils usually contain enough 
of these organisms to accomplish the reduction if adequate organic 
matter is supplied. 
The manure heap presents an additional field for the study of 
nitrate reduction. There are so many factors that can influence 
microbial activities here that conflicting statements have arisen 
regarding the different changes supposed to take place. According 
to the best authorities, there may be some loss from denitrification 
in the surface portion where the air circulates more freely and 
where nitrates may have been formed by nitrification. Deeper 
down in the pile, it is a question whether there is any reduction 
since, except in very 'old manure, there are probably no nitrates 
present owing to the unfavorable conditions for nitrification and 
nitrate formation. On the other hand, in old, well rotted manure, 
where one might expect to find nitrates, there is not enough fresh 
organic matter to stimulate the denitrifying bacteria. 
The Fixation of Atmospheric Nitrogen. 
Separate and distinct from Nitrification, which has been de¬ 
scribed above, is the process of Nitrogen Fixation. The former 
deals entirely with the transformation of nitrogen already present 
in the soil, while the latter is concerned solely with the nitrogen of 
the atmosphere. Nitrification explains how the ammonia nitrogen 
which is obtained from protein decomposition is converted into 
nitrites and nitrates. Nitrogen fixation accounts for the addition 
and accumulation of nitrogen in the soil from the atmosphere. 
The increase in fertility accruing to land fallowed for a number 
