CHAPTER VIII. 

 BACTERIOLOGY OF THE SOIL. 



i. THE bacteriological examination of the soil is one of 

 the most recent branches of scientific study. A good 

 beginning has been made, but a very extensive unex- 

 plored field yet lies before the soil bacteriologist. 



The work carried on by certain groups of organisms 

 has been examined in considerable detail, and the 

 processes of putrefaction and decay of organic substances 

 so far as relates to the nitrogen in them are fairly 

 understood. Much is known also of the nature and 

 causes of nitrification, denitrification, and the fixation or 

 assimilation of the free atmospheric nitrogen by soil 

 organisms ; but many of the problems connected with 

 the formation and decomposition of humus, the chemical 

 changes induced by bacteria and fungi in the mineral 

 constituents of the soil, and the influence of biological 

 processes upon the physical character of the latter await 

 solution. 



Not only is further research needed respecting indi- 

 vidual processes going on within the soil, but systematic 

 study of the various kinds of organisms present in it 

 moulds, algae, and protozoa, as well as bacteria is 

 greatly wanted. The relationship of the work done by 

 each group must be exhaustively investigated, and the 

 relative importance of the various biological processes 

 in the production and maintenance of the fertility of 



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