38 
The: Colorado Experiment Station. 
mechanical, it is a significant fact that bacteria are intimately asso¬ 
ciated with the phenomenon. 
Soil bacteria, like other plants, need a little iron for their 
growth. Lipman and Koch have noted that this is particularly true 
for the nitrogen fixing organisms. 
Calcium {Lime) and Magnesium. 
' So far as furnishing favorable conditions for the growth and 
activity of micro-organisms, the arable soils of Colorado offer all 
that could be desired. The one thing, above all others, which makes 
them especially well adapted to the development of soil bacteria is 
their neutral or alkaline reaction. This is made possible by the pres¬ 
ence of quantities of calcium and magnesium compounds. Frequent 
reference has been made already to the damage which may result 
to an otherwise fertile soil by allowing it to become acid. When 
this condition exists practically all bacteriological processes cease. 
The principal function of the calcium and magnesium carbonates 
is to neutralize the various acids formed during protein-decompo¬ 
sition ; to combine with the nitric acid resulting from nitrification 
by which calcium and magnesium nitrates are formed; and to unite 
with the sulphuric acid set free by the so-called “sulphur bacteria” 
to form calcium and magnesium sulphates. Thus, the soil acids, 
which if allowed to' accumulate might prove detrimental, are neu¬ 
tralized, and all injury to the soil flora from this cause is prevented. 
Although our soils at present are rich in calcium carbonate 
and sulphate, there is nevertheless a large annual loss due to the 
appreciable amounts which are carried away in the drain waters. 
We have seen that carbon dioxide is generated in quantity during 
the fermentation of sugars, starches, etc. When this gas is dis¬ 
solved in water it constitutes carbonic acid, which has a marked 
solvent action upon carbonate of calcium. Through this agency, 
immense caves have been formed in the limestone regions of the 
United States, and tons of rock are transported annually to the 
ocean in solution as the acid carbonate of lime. A small portion of 
this is utilized by the various shellfish in the construction of their 
shells; the remainder goes to form the limestone deposits of future 
generations. 
