CHAPTER IX 
SOME PRACTICAL LESSONS FROM SOIL BACTERIOLOGY 
The close dependence of soil fertility upon the action of micro- 
organisms is manifest, and it is evident that farm processes should 
be such as to stimulate desired bacterial action and check these 
activities that are detrimental. Practical methods of doing this 
have been only partly devised and there are still many problems 
for the future concerning the method of treating soil. Neverthe- 
less, the knowledge of bacterial action has already taught some 
definite and useful lessons. The uncertainty still attached to 
certain phases of the subject may be illustrated by a recently dis- 
covered fact that the sterilizing of certain unfertile soils will 
decidedly increase their fertility. This has been proved definitely, 
but the meaning of the fact is still obscure. Bacterial action is 
positively needed in the soil, and it is rather surprising that steriliz- 
ing soil will increase its fertility. It has been suggested that the 
treatment kills certain injurious bacteria or other microérganisms 
giving the beneficial species that subsequently get in a better op- 
portunity for growth. It is claimed by some that these injurious 
microédrganisms are minute animals (Protozoa) that are harmful 
in soil because they prey upon bacteria and thus hinder the 
normal processes of decomposition. It has been suggested like- 
wise that the sterilization kills all animals and plants that may be 
in the soil, thus giving the bacteria that subsequently get into the 
soil, or that may have resisted the sterilization, an extra amount of 
organic matter to decompose and to reconvert, by nitrification, to 
nitrate. The fact of this beneficial influence of sterilization is 
undoubted, although its explanation is uncertain; and the phe- 
nomenon is here mentioned as an illustration of the gaps still 
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