Sept. ii, 1916 



Bacteriological Studies of a Soil 



959 



The cross-inoculation experiments were tested by taking a mixture of 

 all samples collected during both seasons from the respective plots, 

 thoroughly mixing, and using as a medium 100-gm. samples containing 

 60 mgm. of nitrogen. These samples were also subjected to 20 pounds' 

 pressure for one hour in the autoclave. A sufficient number of samples 

 were thus prepared for duplicate inoculation from each plot under 

 study. One of the duplicates received calcium carbonate; the other 

 did not. These samples were incubated for six instead of four weeks 

 and nitrate nitrogen determined as before. 



In all the above-outlined experiments duplicate samples were set up 

 and analyzed. Where possible, as in the nitrate determinations, dupli- 

 cate determinations were run with each sample. If these varied widely, 

 they were again run; or where this was impossible, they were discarded. 

 In general, the duplicates agreed very well, except in the nitrifying inocu- 

 lating experiments when incubated for only four weeks with no calcium 

 carbonate added. Perhaps these results should not be included in the 

 tabulated data; but since the relative positions of the averages do not 

 materially differ from those of 1914, they have been included. 



EXPERIMENTAL WORK 

 NUMBER OF BACTERIA 



Table II gives the moisture content of soil from the different plots at 

 the various samplings. 



Table II. — Percentage of moisture in soil of the fertility plots when sampled* 



a The soil was dried at 110° C. for two hours. 



Table III gives the total number of bacterial colonies developing on 

 Temple's agar expressed in millions per gram of dry soil. More em- 

 phasis should be placed upon the 191 4 series than the 1913, because of 

 the larger number of analyses and the greater uniformity of plots. A 

 study of this table brings out several interesting facts, the most evident 

 being that of the effect of manure. In all cases except the rotated plot 

 for 1 91 3, all those receiving manure rank materially higher than those 

 not receiving it. Since this exception did not hold true for 1914, it is 

 55852°— 16 3 



