CONTROL AND STIMULATION OF SOIL BACTERIA T3I 
ground shells, or some other common substance. The restora- 
tion of alkaline reaction will be followed by a stimulation of 
bacterial activities and an increased fertility. 
Aeration.—Anaerobic bacteria are not very abundant in 
soil, and their activities are generally harmful. Anaerobic de- 
composition is incomplete, and gives rise to many undesirable 
products, 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 may 
be plenty of organic products in the soil which only need trans- 
forming in order to be available for plants. All desirable processes 
which are likely to occur in the soil are benefited by aeration. In 
especially rich collections of organic refuse, however, like the 
manure heap, aeration will cause large losses through denitrifica- 
tion, and hence the manure should be closely packed to exclude air. 
This may be true also in some instances of intensive gardening, 
where large amounts of manure are applied to the soil as top 
dressing. But in ordinary soil, aeration from frequent stirring 
stimulates desirable bacterial activities. 
Manures Better than Commercial Fertilizers.—This perfectly 
evident conclusion is of so much importance as to deserve special 
emphasis. The reasons for the conclusion are several. Manure 
adds bacteria as well as chemical food. It helps to keep a proper 
alkalinity in the soil. It adds various ingredients that help to 
form humus in the soil, resulting in a better texture and more 
lasting good. Manure adds to the soil in small amounts various 
useful materials, which are not present in commercial fertilizers. 
For these cogent reasons manure fertilizers are to be preferred, 
as a rule, to chemical fertilizers. From all these facts may be 
