SOIL MICROBIOLOGICAL EQUILIBRIUM 749 



of other investigators. 36-39 Bouyoucos 40 and Wilson 41 found an increase 

 in the concentration of the soil solution as a result of heating of soil, 

 using the freezing point method. This increase is greater in soils rich 

 in organic matter than in mineral soils. Heat also effects a floecula- 

 tion of the soil colloids, thus changing the physical condition of the 

 soil. 



The increase in the soluble matter and the changes in the micro- 

 biological population of the soil brought about by heating result in an 

 increase in the numbers of bacteria; these in their turn decompose more 

 organic matter, which results in a greater liberation of available nitrogen. 

 This favors the growth of plants. 42 



Influence of volatile antiseptics upon bacterial activities in the soil. 

 Volatile antiseptics, especially carbon bisulfide, were first applied to 

 soils and plants for the destruction of insect and fungus pests. As far 

 back as 1870 the observation was made that this disinfectant has a 

 stimulating effect upon plant growth. Girard 43 used CS 2 to clear a 

 piece of sugar-beet ground badly infested with nematodes and observed 

 marked increases in the succeeding crops as a result of the treatment. 



36 Whitney, M., and Cameron, F. K. The chemistry of the soil as related to 

 crop production. U. S. Dept. Agr., Bur. Soils, Bui. 22, 1-71. 



37 Lyon, T. L., and Bizzell, J. A. Effect of steam sterilization on the water- 

 soluble matter in soil. N. Y. (Cornell) Agr. Exp. Sta. Bui. 275. 1910; Bui. 

 326. 1913. 



38 Seaver, J. F., and Clark, F. D. Changes brought about by heating of soils 

 and relation to the growth of Pyronema and other fungi. Mycologia, 2: 109- 

 124. 1910; Biocehm. Bui. 1: 413-427. 1912. 



39 Gustafson, 1922 (p. 743). 



40 Bouyoucos, G. The freezing point method as a new means of measuring the 

 concentration of the soil solution directly in the soil. Mich. Agr. Exp. Sta. 

 Tech. Bui. 24. 1915. 



41 Wilson, A. Changes in soils brought by heat. Proc. Roy. Dublin Soc. 

 N. S., 38: 513. 1915. 



42 The favorable influence of heating of soil at temperatures less than 100° 

 upon crop growth has been studied in detail by Russell, E. J., and Petherbridge, 

 F. R. On the growth of plants in partially sterilized soils. Jour. Agr. Sci., 5: 

 248-287. 1913; The practice of burning soils is described by Mann, H. H., Joshi, 

 N. V., and Kanitkar, N. V. The "rab" system of rice cultivation in Western 

 India. Mem. Dept. Agr. India, Chem. Ser., 2: 141-192. 1912; Kelley, W. P., 

 and McGeorge, W. The effect of heat on Hawaiian soils. Hawaii Agr. Exp. 

 Sta. Bui. 30. 1913; Demolon, A. The partial sterilization of peat. Intern. 

 Rev. Sci. Pract. Agr., 3: 431. 1924 (Chem. Abstr., 20: 1878). 



43 Girard, A. Recherches sur l'augmentation des recoltes par l'injection dans 

 le sol du sulfure de carbone a doses massives. Bui. Soc. Nat. Agr. France, 54: 

 356-363. 1894. 



