122 SOME PRACTICAL LESSONS FROM SOIL BACTERIOLOGY. 
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 denitrification, 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 drawn 
the practical lesson that a properly kept farm should keep plenty of 
live stock and, instead of selling its manure, should use it freely on 
the soil. 
FALLOWING. 
It is an old idea that the soil, after yielding several crops, needs 
a rest, an idea that goes back as far as the Romans. From this arose 
the plan of occasionally allowing the soil to remain without a crop 
for a season or for part of a se'ason. This plan has practically 
gone out of use in all ordinary soils, for careful study shows that 
a detriment rather than a benefit results from such fallowing. 
Under certain conditions fallowing may be an advantage. There 
is a smaller loss of water from fallow land than from land with grow- 
ing crops, due partly to the increased evaporation from the stirred 
soil and partly to the fact that crops draw quantities of water from 
the soil, to be evaporated from the growing leaves. In climates 
