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 



