May a8,1917 
Influence of Crop , Season , Water on Soil Bacteria 
307 
these plots to a greater depth than they would in the unirrigated. This 
conclusion is borne out by the results previously published by us (56). 
In this earlier work we took samples to a depth of 10 feet and found that 
there is no loss of nitric nitrogen from these plots during the winter 
months, thus showing that the nitric nitrogen is carried below the 6-foot 
level. 
TABtEJ V .—Nitric nitrogen in alfalfa land—Average for three years 
[Results expressed as pounds per acre] 
Plot No. 
Period. 
1 
Water ap¬ 
plied in five 
applications. 
Depth of soil. 
Total. 
1st foot. 
2d foot. 
3d foot. 
4th foot. 
5th foot. 
6th foot. 
Inches. 
3 1 . 
Spring. 
37-5 
3*6 
1.9 
0. 6 
2. O 
1-4 
I. 0 
72 . 
... do. . .... 
2(. O 
I. 0 
2. 0 
1. 8 
I. 4 
2. K 
I. 4 
11. O 
O'* * . 
33 . 
* 5 * ° 
3-4 
•9 
11. 6 
3*3 
j 
i. 6 
1.9 
22. 7 
...do. 
None. 
10. 0 
c. 1 
11. 4 
2. 2 
0* 3 
6. 0 
44. 0 
0 *T' * ‘ * * . 
3 r . 
Summer... 
37-5 
7 
7 * 1 
J 
2. 5 
2* 5 
1.9 
7 0 
2. 1 
• 4 
16. 5 
32. 
25. 0 
2.4 
3* 2 
2.3 
1. 8 
1.4 
i *5 
12. 6 
33 . 
* 5 * 0 
5*4 
.8 
2.1 
i* 7 
3 * 1 
1.4 
34 . 
None. 
3*3 
8.8 
2. 2 
1.4 
2. 6 
1. 0 
19*3 
3 i. 
Fall. 
37*5 
8.5 
4. 2 
2.4 
3*5 
2.8 
2. 0 
23*4 
32 . 
...do. 
25.0 
14.9 
9.0 
3*2 
2.4 
2. 0 
4*4 
35*9 
33 . 
XT 15 ' 0 
10. 7 
10. 4 
4.4 
2-3 
2.9 
1.8 
32.5 
34 . 
None. 
I 9 * 5 
9 - 7 
6. 5 
3-0 
2.1 
1. 1 
41.9 
The results at first glance might be taken to indicate that the applica¬ 
tion of irrigation water to this soil has retarded nitrification, but it must 
be borne in mind that the nitrogen removed from the irrigated plots was 
much greater than that removed from the unirrigated plot. This nitro¬ 
gen must come either directly from the air through the intervention of 
lower organisms or from the soluble nitrates of the soil. The evidence 
is practically conclusive that the alfalfa plant feeds upon the latter as 
long as it is available and only turns to the atmospheric nitrogen when 
the soil supply has been reduced to a certain low minimum. 
The quantity of nitric nitrogen in the soil decreases as the quantity of 
water applied increases, and this is much more pronounced in the spring 
than it is in the summer or fall. But the influence of the irrigation water 
is quite noticeable throughout the year. The results as a whole clearly 
indicate that the nitric nitrogen of the alfalfa soil is low throughout the 
season, in spite of the fact that the alfalfa is capable of indirectly draw¬ 
ing upon the atmospheric nitrogen. The nitrogen found within the 
alfalfa removed from these plots comes from a number of sources—the 
atmospheric nitrogen, the nitrogen contained within the 6 feet of soil, 
and nitrogen from a depth greater than 6 feet. A comparison of these 
results with those reported where the soil was sampled to a depth of 10 
feet makes the conclusion practically certain that much nitric nitrogen 
