May 28, 1917 
Influence of Crop , Season, Water on Soil Bacteria 
3i5 
PLOTS RECEIVING 37.5 INCHES OP IRRIGATION WATER 
In this series we have alfalfa, potato, oat, com, and fallow plots, each 
receiving 37.5 inches of irrigation water, so that any difference noted 
in the nitric nitrogen of the soil must be due either directly or indirectly 
to the crop growing upon the same. The summarized results for the three 
years are given in Table XV. 
Table XV. —Nitric nitrogen in soil growing various crops and receiving 37.5 inches of 
irrigation water—Average for three years 
[Results expressed as pounds per acre] 
Period. 
Spring.. 
Do.. 
Do.. 
Do.. 
Do.. 
Summer 
Do.. 
Do.. 
Do., 
Do.. 
Fall. 
Do.. 
Do., 
Do.. 
Do.. 
Crop. 
Depth of soil. 
Total. 
istfoot. 
ad foot. 
3 d foot. 
4 th foot. 
5 th foot. 
6 th foot. 
Alfalfa. 
3-6 
I. 9 
0.6 
2. 0 
1*4 
I. O 
*0. 5 
Oats. 
* 3*7 
4*3 
5*9 
1.8 
3*4 
2. 6 
3 i *7 
Com. 
9.1 
3*4 
3*3 
2. I 
i *7 
4. 2 
23.8 
Potatoes. 
11. 4 
12. 2 
2*3 
2.7 
2. 2 
2.9 
33*7 
Fallow. 
15.6 
14 * 5 
10. 7 
5*5 
7.2 
5*9 
59*4 
Alfalfa. 
7 *1 
2*5 
2*5 
1.9 
2.1 
•4 
16. s 
Oats. 
2. 2 
2. 0 
3*2 
1.2 
1.9 
1.8 
12. 1 
Com. 
1. 2 
2.9 
8-5 
4 * x 
4.0 
1.4 
22.1 
Potatoes. 
2. 6 
2. 0 
12. 8 
7*9 
8.4 
4 * 3 
38.0 
Fallow. 
4 * 3 
6.9 
5*3 
9*4 
8.6 
7*2 
42. 2 
Alfalfa. 
8.5 
4. 2 
2.4 
3*5 
2. 8 
2. 0 
23*4 
Oats. 
5*6 
3 *o 
4.0 
2. 8 
2. 5 
2. 5 
20. 4 
Com...*. 
3 *o 
3*6 
2. 7 
2. 0 
2.7 
2.4 
16. 4 
Potatoes. 
9.9 
6. 1 
3 * 7 
4.9 
3 *o 
3*9 
3 1 * 5 
Fallow. 
9*4 
7.2 
7*8 
9.0 
63 
5*3 
45 *o 
There is a marked difference in the quantity and distribution of the 
nitric nitrogen found in the soils growing the various crops. During the 
spring the nitric-nitrogen content of the surface feet of the alfalfa and 
com land is comparatively low, while that of the oat, potato, and fallow 
soil is high. This is especially marked in the case of the last two, for 
here we find over one-half of the total existing within the 6 feet found 
within the first two. But in the summer the nitric nitrogen is carried 
to lower depths by the irrigation water, only to concentrate at the surface 
again during the fall. The total quantity of nitric nitrogen in the alfalfa, 
oat, and com soil is low throughout the year, while the quantity in the 
potato and fallow is comparatively high. It is interesting to note that, 
in spite of the heavy drain which has been made upon the soil-growing 
crops, the nitric nitrogen in the soil during the fall is nearly the same as 
during the spring, while the fallow soil shows a loss of 14.4 pounds during 
summer. This is probably due to the water carrying the nitric nitrogen 
below 6 feet, and the results herein reported point strongly to the con¬ 
clusion that the continuous application of 37.5 inches of irrigation water 
to a soil yearly is going to result in the loss of considerable nitrogen from 
that soil. 
