CONTROL AND STIMULATION OF SOIL BACTERIA. 121 



are checked, while the activities of molds and larger fungi are 

 increased. 



In the soils of forests, for example, the fungi and molds grow 

 luxuriantly, but bacterial action is comparatively slight. While the 

 higher fungi are valuable agents in bringing about the decomposi- 

 tion of certain organic bodies, and are therefore useful, they cannot 

 perform the final transformations by which the soil ingredients become 

 available as plant foods. These transformations, especially nitrifica- 

 tion, require bacterial growth. Hence, it follows that one of the first 

 necessities of proper bacterial activity is an alkaline reaction in the 

 soil. In some localities this matter cares for itself. If the soil 

 contains lime in any form, the solution of lime by the carbonated 

 water, resulting from the carbonic dioxid of decomposition, will 

 keep the soil properly alkaline. Decomposition in itself will also 

 produce an alkaline condition, since the ammonia resulting from 

 ammoniacal fermentation will neutralize the acids. If, therefore, 

 a vigoious decomposition of organic matter is going on, little 

 attention need be given to the matter of acidity. But some soils 

 are acid from one cause or another, and proper bacterial activities 

 cannot be expected here without the correction of this acidity. 

 This is most easily done by the addition of lime, either in the form 

 of limestone, plaster, ground shells, or some other common substance. 

 The restoration of alkaline reaction will be followed by a stimulation 

 of bacterial activities and an increased fertility. 



Aeration. The soil bacteria are aerobic and anaerobic, and both 

 types are sometimes useful and sometimes detrimental. Speaking 

 broadly, however, the aerobic processes in the soil are the more 

 desirable. Anaerobic decomposition is incomplete, and gives 

 rise to many undesirable products, while aerobic decomposition is 

 complete and hence a more useful process. Nitrification, too, 

 can go on only in the presence of oxygen, and is stimulated by a 

 quantity of this gas. The value of a frequent stirring or cultivating 

 of the soil, which introduces air into it, is, therefore, evident. The 

 simple stirring of the soil, to bring oxygen into close contact with its 

 bacteria, may be of as much value as an application of manure. In 

 some soils, indeed, it is more valuable than manure, since there 



