Envir:6 



We were interested scmetime ago in what were the moisture conditions 

 which are limiting to microbiological activity. The soil physicist, in 

 studying moisture, as far as plant growth is concerned, has pretty well 

 come to the conclusion that moisture tension is the best measure of 

 available water to the plants. This moisture tension, I am sure, has a 

 lot to do with how fast moisture will migrate from one place in the soil 

 to the place where plant roots are and where it is taken up. There is 

 this translocation process of water uptake and movement through the plant 

 which is a limiting factor. The microbes, however, live in the film of 

 water apparently unrestricted by the factors which affect the higher 

 plants. He are, therefore, interested in finding out if tension is the 

 important thing about soil moisture; or is there some other factor? In 

 Tables 3 and U I have given some figures which will help to illustrate, 

 at least, the conclusions we came to. 



Table 3. 



Relat-i-ve Humidity, Moisture Content, 

 and Rate of Decomposition (2$Q C.) 



Plant 

 Material 



Relative 

 Humidity / 



Moisture 

 Content % 



Mg. CO2 in 

 192 hours 



In Table 3 we have the situation where a uniform relative humidity was 

 maintained and various plant residues were incubated in equilibrium with 

 this particular relative humidity. You will note, however, that the 

 moisture content of the plant matei-dals varied widely although the rela- 

 tive humidity was kept constant. Note that also the overall activity of 

 the microflora inhabiting these residues was proportional sOTiiewhat to 

 the moisture content; it was not a direct function of the moisture ten- 

 sion (relative humidity). Those plant materials that absorbed more 



