I30 SOME PRACTICAL LESSONS FROM SOIL BACTERIOLOGY 
foods. These bacteria are commonly abundant enough; and 
sometimes they find the conditions so favorable that they grow 
rapidly, producing vigorous actions; but at other times the condl- 
tions in the soil are unfavorable, and they are heldin check. What 
is chiefly needed, then, in the treatment of soil is, not the inocula- 
tion of more bacteria, but a modification of the soil conditions so 
as to favor the growth of those already there. While this is a 
complicated subject and one that will require different treatment 
in different cases, a few general principles may be formulated. 
Acidity —Most bacteria, and practically all the useful bac- 
terla, are very sensitive to the presence of acid, failing to grow at 
all in an acid medium. If the soil is but slightly acid, bacterial 
agencies are checked, while the activities of molds and larger 
fungi are increased. 
In the soils of forests, for example, the fungi and molds grow 
luxuriantly, but bacterial action is comparatively slight. While 
the higher fungi are valuable agents in bringing about the de- 
composition of certain organic bodies, and are therefore useful, 
they cannot perform the final transformations by which the soil 
ingredients become available as plant foods. These transforma- 
tions, especially nitrification, require bacterial growth. Hence, 
it follows that one of the first necessities of proper bacterial ac- 
tivity is an alkaline reaction in the soil. In some localities this 
matter cares for itself. If the soil contains lime in any form, the 
solution of lime by the carbonated water, resulting from the car- 
bonic dioxid of decomposition, will keep the soil properly alkaline. 
Decomposition in itself will also produce an alkaline condition, 
since the ammonia resulting from ammoniacal fermentation will 
neutralize the acids. If, therefore, a vigorous decomposition of 
organic matter is going on, little attention need be given to the 
matter of acidity. But some soils are acid from one cause or 
another, and proper bacterial activities cannot be expected here 
without the correction of this acidity. This is most easily done 
by the addition of lime, either in the form of limestone, plaster, 
