INFLUENCE OF ENVIRONMENTAL CONDITIONS 785 



tends to improve the physical condition of the soil; it brings about a 

 rapid drying of the surface layer of the soil and, when moistened by 

 rainfall, bacterial activities are stimulated. Prolonged drought brings 

 about similar results in a still more pronounced way. 64 Greater num- 

 bers of microorganisms were found in cultivated than in uncultivated 

 soils. 65 ' 66 The efficiency of the soil for nitrate production is increased 

 by cultivation and aeration. 67 



The following quantities of aerobic bacteria (growing on the common 

 plate) were recorded 68 in 1 gram of moist soil: 



Raw peat, undrained 138,500 



Drained, but not cultivated 200,300 



Freshly cultivated, treated with lime and sand 6,900,400 



Cultivated for some time, limed, manured 6,224,500 



Same, fallowed 7,801,600 



In comparing the bacteria in soils from under corn and under alfalfa, 

 greater numbers of organisms were found 69 to be present in the first 

 three feet of corn soil than in the same layer of alfalfa soil; this is prob- 

 ably due to better aeration of the corn soil brought about by the soil 

 treatment. 



The number of organisms in cultivated soils may be twice as large 

 as in corresponding virgin soils, and higher in wheat land than in 

 alfalfa land. 70 Nitrification and nitrogen-fixation were also twice as 

 active in land under cultivation. The beneficial effect of summer 

 fallowing and disking was believed to be due, in part at least, to 

 increased available plant food in cultivated soil, brought about by 

 increased bacterial activities. 



Fallowing has a favorable influence on nitrate formation and rapidity 

 of decomposition of the organic matter in the soil. 71 Caron's results 



« Caron, 1895 (p. 772). 



66 Houston, 1898 (p. 14). 



67 Lyon, T. L. Intertillage of crops and formation of nitrates in soils. Jour. 

 Amer. Soc. Agron., 14: 97-109. 1922. 



08 Fabricius, O., and von Feilitzen, H. tlber den Gehalt an Bakterien in jung- 

 friiulichem und kultiviertem Hochmoorboden auf dem Versuchsfelde des Schwe- 

 dischen Moorkulturvereins bei Flahult. Centrbl. Bakt. II, 14: 161-168. 1905. 



69 Waite, H. H., and Squires, D. H. A comparative study of the bacterial 

 content of soils from fields of corn and alfalfa. Nebr. Agr. Exp. Sta., 24th Ann. 

 Rpt., 160-177. 1911. 



70 Greaves, J. E. A study of bacterial activities in virgin and cultivated 

 soils. Centrbl. Bakt. II, 41: 444-459. 1914. 



71 Ehrenberg, P. Uber den Stickstoffhaushalt dea Ackerbodens. Fiihlings 

 landw. Ztg., 58: 241-246. 1909. 



