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 activi- 
ties 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. Nevertheless, the knowl- 
edge 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 discovered 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 sterilizing soil will increase its fertility. 
It has been suggested that the treatment kills injurious bacteria, 
giving the beneficial species that subsequently get in a better op- 
portunity for growth. It has been suggested likewise 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 phenomenon is here mentioned as 
an illustration of the gaps still existing in our knowledge of soil 
bacteriology. But in spite of it all, some definite conclusion as well 
as practical lessons can already be drawn.* 
* Reference should be made here to the conception concerning soil fer- 
tility held by some, notably those connected with the Bureau of Soils of 
the Department of Agriculture, that the primary trouble in "worn-out 
soils" is not lack of sufficient plant food, but the presence of poisonous 
excretions that prevent the growth of plants. It is claimed that each crop 
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