May 28,1917 
Influence of Crop , Season , PVater on Soil Bacteria 
335 
single exception of potato plots in the summer, this same statement 
holds for the nitrifying powers of the soil. These results would appear 
to be absolutely contrary to the findings of Heinze (24), Russell (48), and 
others (5, 47), who have found fallow to increase not only the number but 
all the bacterial activities of the soil. But it must be remembered 
that these investigators were working with soil which was alternately 
fallowed and cropped, and on this there would be left plant residues, 
while we have been working with a soil which has been continually 
fallow for 12 years, the organic matter of which has been reduced to a 
minimum. The results do, however, show the contentions of Hiltner 
to be unfounded, for the low nitrate content of alfalfa is due to the plant's 
rapidly removing the nitrates as formed and not due to the lack of 
nitrifying powers in the alfalfa soil. 
COMPARISON OP BACTERIAL ACTIVITIES AND CROP PRODUCED ON SOIL 
It is interesting to compare the nitric nitrogen found in the soil and 
the nitrogen removed in the crop with the various bacterial activities. 
In order to make these results more comparable, the average nitric 
nitrogen and nitrous nitrogen in the soil, the nitrogen removed in the 
crop, the number of organisms developing on synthetic media, the 
ammonia and nitric nitrogen produced in the laboratory by the fallow 
soil and the unirrigated soil have been taken as 100 per cent, and each 
of the cropped and irrigated soils compared with these. The summarized 
results are given in Table XXXIV. 
Table XXXIV .—Comparison of bacterial activities and crop produced on soil 
Crop or treatment. 
Nitric nitro¬ 
gen in soil. 
Nitrous ni¬ 
trogen in soil. 
Bacterial 
colonies. 
Ammonify¬ 
ing powers. 
Nitrifying 
powers. 
Per cent . 
Per cent. 
Per cent . 
Per cent. 
Per cent. 
Fallow. 
IOO 
IOO 
IOO 
IOO 
IOO 
Alfalfa. 
36 
233 
163 
76 
148 
Oats. 
36 
167 
136 
*5 
103 
Com... 
33 
56 
127 
84 
77 
Potatoes. 
99 
122 
141 
90 
261 
No water. 
IOO 
IOO 
zoo 
IOO 
IOO 
15 inches. 
48 
US 
99 
103 
9 ** 
25 inches. 
SI 
62 
95 
96. 6 
9 o 
37.5 inches... 
43 
US 
93 
104 
98 
Nitrogen in 
crop. 
Per cent. 
IOO 
140 
140 
145 
These data show that the crop has reduced the quantity of nitric nitrogen 
of the soil, but has increased the efficiency of the nitrifying bacteria, owing 
to the removal of the nitrate producer, while, on .the contrary, oats and 
alfalfa have increased the nitrous-nitrogen content. That this is due to 
the compact nature of the soil is seen from the results, for the nitrous 
nitrogen increases as the aeration of the soil decreases and is very pro¬ 
nounced in the alfalfa. In the potato soil, which is cultivated, it is less than 
