128 EFFECT OF HEAT ON SOIL BACTERIA 



of wheat grain and of 21 to 80 per cent, in wheat straw. The yield 

 of potatoes was similarly increased by 5 to 38 per cent, and that of 

 beets from 18 to 29 per cent. Although the yields of the legumes 

 were not always increased, yet some fields of clover treated with 

 carbon bisulphid gave increases of 119 per cent. 



Wollny clearly showed that the application of carbon bisulphid to 

 a soil within the growing season may lead, according to the amount 

 introduced, to a complete destruction of the growing crop, or to 

 a temporary retardation merely, involving a greater or slighter 

 depression in the production of plant substance. Its application 

 several months before planting increases the fertility of the soil 

 to a considerable extent. This influence is felt, according to the 

 amount of carbon bisulphid used, through one or several growing 

 seasons, after which if no manure or fertilizer has been applied a 

 marked decrease in the yields becomes evident. 



There was the dark green color and the vigorous development of 

 the plants together with the decided tendency of grain crops to 

 lodge just as if too great quantities of nitrogen were at their disposal. 

 These facts led Heinze to conclude that on the whole we must seek 

 the cause of the beneficial effect of carbon bisulphid on the soil in 

 the enormous increase of soil organisms at the proper time, thus 

 rendering available, or possibly increasing, the nitrogen supply to 

 growing plant. 



The large amounts of nitrogen thus made available to the crops 

 are derived partly from the soil and partly from the atmosphere. 

 Kruger and Heinze not only demonstrated that soils treated with 

 carbon bisulphid showed an increase in their total nitrogen content, 

 but also that the increase was the result of the more vigorous growth 

 of the nitrogen-fixing Azotobacter species. This, Heinze considers, 

 resulted from the initial suppression of amid-ammonia formation 

 and nitrification which would create favorable conditions for the 

 development of nitrogen-fixing flora. Later there would be more 

 intense transformation of the bacterial proteins and of other nitrog- 

 enous organic substances into amino- and ammonia compounds 

 which would result in a more vigorous nitrification, thus placing 

 at the disposal of the plant an abundant and uniform supply of 

 soluble nitrogen compounds. The various organic materials in the 

 soil such as plant residues, pectins, pentosans, humic substances, 

 and the like, together with the rapid growth of algse and molds- 

 may furnish the carbon food for the Azotobacter species. 



Effect on Properties of Soil. Egoro w, who investigated the effects of 

 carbon bisulphid upon the physical properties of the soil, found that 

 (1) the capillary rise of water in the soil treated with carbon bisul- 

 phid to be slower than in the untreated ; (2) the moisture content 

 is reduced considerably, especially in peaty soils; and (3) the water- 

 holding capacity of the soil is decreased. Thus, he concludes that 



