746 



PRINCIPLES OF SOIL MICROBIOLOGY 



that heating of soil increased the solubility of the mineral constituents 

 and organic matter in the soil, and soil productivity. Kriiger and 

 Schneidewind 24 also suggested that the favorable effect of heat is due 

 to the increase in the solubility of soil minerals, as shown in the 

 following summary: 



Yield of mustard, in grams per pot 



It was later found that heating of soil brings about a decided change 

 in its microbial population, as pointed out above. On subsequent 

 remoistening of the soil, the greatest increase in the numbers of micro- 

 organisms is shown by the non-spore forming bacteria; the actino- 

 myces increase only slowly, while the fungi and protozoa destroyed by 

 the treatment reappear only later. The fungi once introduced make 

 a very rapid growth on soil sterilized by heat. 25 Sterilization by heat 

 results also in the destruction of the nitrifying bacteria; it brings about 

 a decided increase in the amount of ammonia accumulated in the soil, 

 due to a greater decomposition of the soil organic matter by the micro- 

 organisms. 26 This accounts for the increased fertility of the soil and 

 beneficial influence upon plant growth which results from the steaming 

 of the soil. 27 



Fischer 28 observed that when a soil is sterilized by means of steam and 

 reinoculated with bacteria, a great increase in biological activities results ; 

 this can be determined by the increase in numbers and by the production 

 of carbon dioxide. After some time (three weeks), the bacterial num- 

 bers still remain at a high level while the production of carbon dioxide 



24 Kriiger, W., and Schneidewind, W. Ursache und Bedeutung der Sal- 

 peterzersetzung im Boden. Landw. Jahrb., 28: 277-252. 1899. 



25 This phenomenon is readily observed also in field soils, which became sub- 

 ject to considerable heat for one reason or another: Tokugawa, Y., and Emoto, 

 Y. Uber einem kurz nach der letzten Feuerbrust plotzlich entwickelten Schim- 

 melpilz. Japanese Jour. Bot., 2: 175-188. 1924. 



26 Russell and Hutchinson, 1909 (p. 311). 



27 Elveden, V. A contribution to the investigation into the results of partial 

 sterilization of soil by heat. Jour. Agr. Sci., 11: 197-210. 1921. 



28 Fischer, H. Versuche iiber Bakterienwachstum in steriliziertem Boden. 

 Centrbl. Bakt. II, 22: 671-675. 1909. 



