MICROBIOLOGICAL ANALYSIS OF SOIL 709 



physico-chemical condition of the soil and its flora and fauna are 

 affected in such a manner as to bring about increased activities of 

 certain groups of microorganisms, accompanied by a greater decomposi- 

 tion of the soil organic matter; this results in the liberation of nitrogen 

 in an available form and in increased crop growth. Whether growth of 

 cultivated plants in the so-called "sick" or "exhausted" soils is due 

 to the development of parasitic fungi or of organisms competing with 

 the bacteria for the plant food, or of organisms actually destroying the 

 bacteria, or whether this is due to the formation of toxic substances 

 by microorganisms in the soil, there is no doubt that, by modifying the 

 microbial flora and fauna and their activities, through heat or treat- 

 ment with antiseptics, more favorable conditions for plant growth 

 will result. 



In considering the soil microflora as a whole, can a group of methods 

 be suggested, which would supply the information necessary for an 

 understanding of the various processes carried on by microorganisms 

 in the soil, so as to obtain an insight into the actual or potential fer- 

 tility of the particular soil? The methods for measuring the biological 

 activities of the soil should be quantitative, both for the study of 

 numbers of all or of certain specific types of microorganisms and for 

 measuring the physiological activities of the microorganisms, both in the 

 soil as a whole and under specifically controlled laboratory conditions. 

 However, since soil fertility is affected, aside from the biological activi- 

 ties, also by the physical and chemical soil conditions, nature of crop, 

 weather, etc., the results should not be expected to represent a mathe- 

 matical function of crop productivity of a given soil. The results 

 obtained from the study of one group of soils may not necessarily 

 apply to other soils, under different climatic, topographic and other 

 conditions. The mechanical composition, reaction, presence of free 

 salts, as well as the physico-chemical condition of the soil, are of great 

 importance in this connection. 1 



Methods for determining the microbiological condition of the soil. Ac- 

 cording to Niklewski, 2 the value of microbiological methods for soil 

 characterization is largely due to the fact that we are able to determine 

 the properties of a soil more exactly than by ordinary methods of 

 chemistry and physics. Christensen 3 also states that the microbiologi- 



1 See Lohnis, F. Ziele unci Wege der bakteriologischen Bodenforschung. 

 Landw. Jahrb., 42: 751-765. 1912. 

 * Niklewski, 1912 (p. 726). 

 3 Christensen, 1915 (p. 578). 



