126 



EXPERIMENT STATION. 



[Jan. 



INFLUENCE OF SOIL DECOCTIONS FROM STER- 

 ILIZED AND UNSTERILIZED SOILS UPON 

 BACTERIAL GROWTH. 



C. A. LODGE AND R. G. SMITH. 



An attempt has been made in the following experiments to 

 ascertain the cause underlying the effects which sterilized and 

 unsterilized soil decoctions have upon bacterial develoi^meiit. 

 These questions have often arisen: In what maimer does soil 

 sterilization affect bacterial development ? Is the cause under- 

 lying the development of bacteria in soils of a chemical or bio- 

 logical nature ? Some investigators maintain that the increase 

 of bacteria in sterilized soils is due to a chemical stimulus, while 

 others insist that it is biological ; i.e., that minute animal organ- 

 isms known as protozoa affect the bacterial flora of soils. In all 

 probability the chemical factor is the important one, the bio- 

 logical factor playing little or no part in either increasing or 

 retarding bacterial growth, at least in any of our soils. 



We selected for use in our experiments two types of soils, — 

 one an Amherst greenhouse soil or loam, somewhat modified by 

 the addition of coarse sand and quite rich in organic matter, and 

 which will be designated as loam ; and the other a yellow loam 

 or a typical Amherst subsoil, deficient in nitrogen and contain- 

 ing only a slight amount of organic matter, which will be desig- 

 nated as subsoil. 



Table I. — Showing Mechanical Analysis of Two Types of Soils used in 



these Experiments. 



[Per cent, of organic matter, gravel, sand, silt and clay in 20 grams of soil.) 



' This work was done at the instigation and under the direction of Dr. C!. E. Stone when Messrs. 

 Smith and Lodge were seniors in the college. 



