202 BACTERIA AND SOIL FERTILITY 



The gain of nitrogen in this soil was at its maximum when the 

 soil extract had been heated to 60 '^ C. Above or below this tem- 

 perature there was a decrease in the fixation of nitrogen. 



Some workers have found that heat decreases the denitrifying 

 organisms of the soil. Moreover, most workers have found that 

 heating of a soil causes a disappearance of the microfauna, espe- 

 cially the protozoa. 



Other workers claim that the heating of the soil removes from 

 it certain poisonous substances which have accumulated from the 

 growth of specific plants, which, if permitted to remain in the 

 soil, interfere with plant growth. It is quite evident from the 

 preceding brief summary that the heating of soil changes pro- 

 foundly both its chemical and biological composition. 



Antiseptics.— Carbon bisulfid and other volatile antiseptics are 

 often applied to plants, and indirectly they find their way into 

 soil or else are added directly to the soil for the purpose of killing 

 parasites. Carbon bisulfid was first used by Oberlin, an Alsatian 

 vinegrower, to free his vineyard of phylloxera and later by Ge- 

 rard to clear a piece of sugar-beet land badly infected with nema- 

 tode. Both observers found that subsequent crops were bigger 

 and better. From this observation Oberlin founded his system of 

 grape culture in which carbon bisulfid was used to replace fallow- 

 ing and rotation in the resetting of vineyards. Since that time 

 many workers have observed that carbon bisulfid, toluene, ether, 

 and other volatile antiseptics greatly increase the productivity of 

 the soil. 



Koch found that the use of carbon bisulfid at the rate of 2904 

 pounds an acre resulted in a gain of 15 to 46 per cent in the 

 yield of wheat grain and from 21 to 80 per cent in the yield 

 of straw. The yield of potatoes was similarly increased by 

 5 to 38 per cent and that of beets from 18 to 29 per cent. Al- 

 though the yields of the legumes were not always increased, yet 

 some fields of clover gave increases of 119 per cent. The in- 

 fluence is perceptible according to the amount of carbon bisulfid 

 used throughout one or several growing seasons, after which if no 

 manure or fertilizer is applied a marked decrease in the yields 

 becomes evident. 



