740 



PRINCIPLES OF SOIL MICROBIOLOGY 



of microorganisms can also be obtained, however, by treatment of 

 soil with various volatile antiseptics, heating the soil or even merely 

 drying it. The resulting activities are similar to those following the 

 addition of a fresh supply of energy, as shown in the following pages. 

 Influence of air-drying of soil upon the microbiological equilibrium. 

 The favorable effect of drying of soil upon the growth of higher plants 

 has been reported from various sources. 4 This effect was first attributed 

 to the improvement in the physical condition of the soil, especially in 



Fig. 63. Course of biological activities in undisturbed soil (from Waksman and 

 Starkey). 



case of fine grained soils, then it was ascribed to some chemical change 

 in the soil as a result of drying. The numbers and activities of micro- 

 organisms are found to be markedly influenced by the drying of the 

 soil. When one part of the same soil is allowed to remain moist and 

 the other part is air dried for some time and then moistened, a rise 

 in the numbers of bacteria and an increase in the evolution of carbon 



4 Lebedjantzev, A. N. Drying of soil, as one of the natural factors in main- 

 taining soil fertility. Soil Sci., 18: 419-447. 1924. 



