May as. 1917 Influence of Crop , Season , Water on Soil Bacteria 323 
receiving the greatest quantities of water. During the spring and sum¬ 
mer the nitrifying powers of the soil are quite regularly increased by the 
irrigation water. But apparently the water in the soil where the 37.5 
inches are being applied toward fall becomes sufficient to depress greatly 
its ammonifying powers. This, however, may be due to the continual 
washing of the nitrifying organisms to below 12 inches. . 
There is a marked relationship between the number of organisms and 
the ammonifying powers of the soil, but the nitrifying powers show no 
relationship to either. 
POTATO LAND 
The plots in this series were each planted to potatoes, and all received 
the same cultivation and general treatment, with the exception of water 
applied, which varied from no irrigation to 37.5 inches per year. The 
average results for the three yearS are given in Table XXIII. 
Table XXIII .—Number of colonies of bacteria , milligrams of ammonia , and milligrams 
of nitric nitrogen from soil receiving varying amounts of waiter. Crop, potatoes. Aver¬ 
age for three years 
NUMBER OP COLONIES DEVELOPED IN 4 DAYS ON SYNTHETIC AGAR PER GRAM OP SOIL 
Plot No. 
Water 
applied. 
Sampled 
May 1 . 
Sampled 
Aug. 1 . 
Sampled 
Nov. 28 . 
Average. 
35 . 
Inches. 
37 - 5 
4, 933 * °°° 
5, 666, 000 
5,833, 000 
5, 766, 000 
4 , 533 ?000 
5, 077, 000 
36 . 
25.0 
7, 000, 000 
5, 067, 000 
4, 000, 000 
5, 555,000 
37 . 
J 5* 0 
4, 800, 000 
5,233,000 
38. 
None. 
7,167, 000 
6, 500, 000 
5 > **33 > 000 
6 ,500,000 
MILLIGRAMS OP AMMONIA PRODUCED IN IOO GM. OP SOIL IN 4 DAYS 
35 . 
37-5 
50.3 
67.9 
53-3 
57*2 
36. 
25. 0 
63.0 
66.3 
48. 5 
59 * 2 
37 . 
15-0 
51.2 
57*4 
38.7 
49 * 1 
38. 
None. 
5 6 *4 
65.0 
50. 6 
57*3 
MILLIGRAMS OP NITRIC NITROGEN PRODUCED IN IOO GM. OP SOIL IN 21 DAYS 
35 . 
37*5 
4. 0 
10. 2 
2. 2 
5 * 5 
36 . 
25. 0 
4*3 
17.8 
10. 4 
10. 8 
37 . 
15. 0 
2. 6 
20. 6 
6. 0 
9*7 
38....,. 
None. 
1. 1 
13. 6 
3*8 
6. 2 
The relationship between the water applied and the number of bacteria 
is not as well defined in the potato as in the alfalfa soil; but even in the 
potato plots the tendency is for the larger quantities of water to depress 
the number of bacteria. The number of organisms is slightly higher in 
the spring than in the fall, and the difference which is noted in the fall 
appears again in the spring. The number found in the summer is con* 
siderably higher than the number found in either fall or spring. The 
results as a whole indicate that the water has decreased the number of 
organisms in the first foot. 
