SOIL MICROBIOLOGICAL EQUILIBRIUM 



741 



dioxide and in the accumulation of nitrates is found to take place in 

 the second soil. The rise in the numbers and activities of microorgan- 

 isms is soon followed by a rapid fall until they approach those of the 

 control soil. When the formation of acid in glucose solution and 

 ammonia in urea and peptone solutions were used as indices, an air-dried 

 soil was about 20 per cent more active than the corresponding 



iuj| L I B R A R 



Fig. 64. Influence of length of air-drying of soil upon its biological activities; 

 as indicated by the evolution of C0 2 (from Waksman and Starkey). 



moist soil. 5 Different soils behave differently in this respect, heavy 

 soils showing greater differences than light soils; the difference was 

 particularly noticeable in garden soils. The bacteriological methods of 

 analysis were found very unsatisfactory and Rahn, therefore, ascribed 

 the beneficial effect of drying to the degree of solubility of minerals. 



6 Rahn, O. Bakteriologische Untersuchung uber das Trocknen des Bodens. 

 Centrbl. Bakt. II, 20: 38-G1. 1908. 



