EXPERIMENT STATlUN REPORTS. 151 



iu Delfl. By iurtuondn"- iiitelli<>ontIy IIk' liCc eoiulilions of hacleria, 

 such as oxygen and TcxkI siijtply, 1('iii|i('raliii-(> and many ollici' factors, 

 lie M-as able to j)iXMlict and to oblain willi niallicmal ical sni-cly (lie pre 

 dominating flora. 



In such experiments as this on the nature of 1he water, Soil-liac- 

 Icriological Science finds its greatest ])r()mise. 



if we ask ourselves: What is the nltiniale aim of (he apjdied science 

 of Soil Bacteriology?, the answer must be: The aim of Soil JJacteriology 

 (aside from the purely' scientific interest) is to j)ut the action of the 

 soil bacteria in the service of agriculture, to suppress the detrimenlal 

 species and (lieir action, and to encourage the beneficial bacteria like 

 those which accumulate niirogen, and such as make available those com- 

 pounds of the soil which are in a. state not available for plant nourish- 

 ment. 



To accomplish this, or, in other words, to influence the microorganisms 

 in the soil intelligently, presupposes the necessary knowledge of the 

 environment of the bacteria, of those factors, which are at our com- 

 mand, that can be varied as Ave desire, such as oxygen supply, water, 

 reaction, etc. 



Let us now consider the soil and let us treat it from the ])oint of 

 view of a medium for the microflora. Soil is composed of three states 

 of material, solid material, water and air; and these three states have 

 a marked intlnence on each other. The soil bacteria are living in the 

 soil water, but this soil water is influenced very markedly by the solid 

 material and by the air. It is this that makes the soil a difficult medium 

 to investigate. T miglit say here that I know of no medium that is so 

 variable and c(!niplex as soil. If we consider milk in this respect, the 

 air, and the solid substances, play only a very small role. It can also 

 be said that the milk of different cows does not differ materially as a 

 medium for the bacteria. On the other hand, we know how large are the 

 differences in soils vrhicli must necessarily influence their microflora. 



We encounter still another difficulty if we remember the fact that our 

 medium (the soil) is very difficult to sterilize. Only by the action of 

 powerful agents are we able to sterilize the soil, in fact, the changes, 

 which are necessarily brought about by this sterilization process, are so 

 marked that we doubt even if we may call this sterilized medium, soil. 



This means that in the case of soils we are practically deprived of 

 the opportunity of recording the action of single species of microorgan- 

 isms. Further, soil is especially characterized by enormous surfaces. 

 To give an idea how great the soil surface is, I should like to cite the 

 work of Alfred Mitscherlich^ who came to the conclusion that the outer 

 surface of one gram of quartz sand was 1.38 square meters and that of 

 one gram of clay was 96G.7 square meters. These enormous surfaces 

 give us an idea of how closely the soil water can be in contact with 

 the solid soil substance. 



In regard to the permeability, I regret to say that Ave have but very 

 little trustworthy data. The reason for this is evident, namely, that 

 the many values obtained with air-dried soil do not permit any con- 

 clusions for field conditions. We may say, however, that the permeability 

 of the different soils is extremely variable. 



From the foregoing, it is clear that, even in fine tertiary quartz sand, 



3A. Mit.scheriich, Bodenkunde fur Land und Forstwirte, 1005, pp. 49-73. 



