CONTROL AND STIMULATION OF SOIL BACTERIA. 121 
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 decomposi- 
tion 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 transformations, especially nitrifica- 
tion, require bacterial growth. Hence, it follows that one of the first 
necessities of proper bacterial activity 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 carbonic 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 vigoious 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, ground shells, or some other common substance. 
The restoration of alkaline reaction will be followed by a stimulation 
of bacterial activities and an increased fertility. 
Aeration. The soil bacteria are aerobic and anaerobic, and both 
types are sometimes useful and sometimes detrimental. Speaking 
broadly, however, the aerobic processes in the soil are the more 
desirable. Anaerobic decomposition is incomplete, and gives 
rise to many undesirable product's, while aerobic decomposition is 
complete and hence a more useful process. Nitrification, too, 
can go on only in the presence of oxygen, and is stimulated by a 
quantity of this gas. The value of a frequent stirring or cultivating 
of the soil, which introduces air into it, is, therefore, evident. The 
simple stirring of the soil, to bring oxygen into close contact with its 
bacteria, may be of as much value as an application of manure. In 
some soils, indeed, it is more valuable than manure, since there 
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