Aug. 1909.] 



Soil Bacteriology. 



213 



Subplots 1A and IB remained in the original condition 

 and received no treatment, except to keep the weeds down. 

 This was done by shaving them off at the surface of the 

 ground with a hoe. The remainder of the subplots, from 2 

 to 6 of both A and B, were stirred to a depth of two inches 

 after every rain, as soon as the soil was dry enough to till. 

 Subplots 2, 3, 4, 5 and 6, of both A and B, were plowed to a 

 depth of two, four, six, eight and ten inches, respectively. 



In order to determine the influence of the different depths 

 of cultivation on the number of bacteria, six samples were 

 taken from each subplot every seventh day. These samples 

 were taken every second inch to the depth of twelve inches. 

 The estimates are given as so many million bacteria per cubic 

 centimeter. The high bacterial content obtained in some in- 

 stances is perhaps due to the methods used in this work. The 

 volumetric method of collection and preparation of samples 

 was used exclusively. 



At the same time that samples were taken for bacterial de- 

 termination, samples were also taken to determine the per 

 cent, of moisture in the surface foot of the soil. Each plot 

 was provided with a thermometer, so that the temperature 

 could be recorded each time the samples were taken. The 

 results are given in the following tables (I to XII) : 



TABLE I PLOT A. Check plot, undisturbed. Fine sandy loam (U. S. Soil Survey). Number 

 of bacteria given as millions per cubic centimeter. 



1. Determinations made on March 19 indicate number of bacteria at beginning of experiment . 



2. Samples taken after field had been saturated for several days. 



Moisture estimates indicate per cent, average in first foot, one determination being made for 

 all plots. 



In all cases "x" indicates a spreading growth on plate cultures which prevented counting 

 of colonies. 



