130 



EFFECT OF HEAT ON SOIL BACTERIA 



3. A slight initial increase in ammonia content, followed by a 

 considerable increase in the production of ammonia. This, although 

 noted by the majority of workers, is especially brought out by the 

 work of Russell and Hutchinson, as is illustrated by the following 

 results from their work: 



4. A depression of the processes by which ammonia is converted 

 into nitric acid, and a very slow recovery of the activity of the bac- 

 teria concerned, as a result of which ammonia accumulates in the 

 soil. Warington, in his early investigation on the biological nature 

 of nitrification, observed that when air containing carbon bisulphid 

 was passed through the soil the process was inhibited, whereas C. 

 de Briailles noted that during the winter the carbon bisulphid seemed 

 to exert a harmful influence on the accumulation of nitrates. How- 

 ever, with the first open weather in spring the reverse seemed to be 

 true the carbon bisulphid caused a marked increase in nitrates over 

 the untreated. 



5. An increase in the rate at which oxidation takes place in the 

 soil. In a study of oxidation in soils and its relationship to produc- 

 tiveness, Darbishire and Russell found that the absorption of 

 oxygen by soil is mainly brought about by the action of micro- 

 organisms and is greatly diminished if the soil has been previously 

 heated to 120 C. When heated to 95 C., it was found that the 

 rate of oxidation on a sand, two loams, and a chalky soil, instead of 

 being reduced was considerably increased, as was the case after 

 treatment with and removal of volatile antiseptics, such as toluene, 

 chloroform, carbon bisulphid, and other volatile antiseptics. 



The rates of oxidation of heated soils were as follows : 



Milligrams of oxygen absorbed in 



Hop garden soil, unheated . 

 Hop garden soil, heated to 95 C. 

 Garden soil, unheated 

 Garden soil, heated to 95 C. 



3 days. 

 3.7 

 6.0 

 7.5 



16.9 



6 days. 



5.2 



8.2 

 10.2 

 27.2 



9 days. 



7.0 

 12.0 

 15.5 

 33.2 



