33° Journal of Agricultural Research vot. ix, no. 9 
of the cropped plots contain a greater number of organisms than does 
the fallow, which would indicate that the limiting factor is more pro¬ 
nounced in its effect in fall on fallow soil than on cultivated soil. 
Table XXIX.-— Number of'colonies of bacteria, milligrams of ammonia, and milli¬ 
grams of nitric nitrogen from soil with various crops receiving 37.5 inches of irrigation 
water 
NUMBER OF COLONIES DEVELOPED IN 4 DAYS ON SYNTHETIC AGAR 
Plot No. 
Crop. 
Sampled May 1. 
Sampled Aug. 1. 
Sampled Nov. 
28. 
Average. 
31. 
Alfalfa. . 
6, 700, 000 
6, 133, 000 
6, 700,000 
4,933,000 
8, 266, 000 
6, 433, OOO 
6,000, 000 
6,866, 000 
5, 766, OOO 
6,933)000 
2, 800, OOO 
4,133) 000 
3 ) 333)000 
4 , 533 ) 000 
2,200,000 
; 
5,311,000 
5, 422,000 
5, 633, 000 
5,077, 000 
5, 799, 000 
1 
4 ?, , .. .. 
Oats 
Com 
2 cr . 
Potatoes... 
Fallow.... 
?Q. 
V/ . 
31 
43 
47 
35 
39 
MILLIGRAMS OF AMMONIA PRODUCED IN IOO GM. OF SOIL IN 4 DAYS 
Alfalfa. 
50. 5 
46. 0 
43 - 2 
46.6 
Oats. 
56.8 
69-3 
49. 6 
58.6 
Com. 
50.5 
59 -1 
46. 7 
52. 1 
Potatoes. .. 
50.3 
67.9 
53 * 3 
57 - 1 
Fallow.... 
66.2 
69.4 
49. 6 
61. 7 
MILLIGRAMS OF NITRIC NITROGEN PRODUCED IN IOO GM. OF SOIL IN 21 DAYS 
Alfalfa. 
3-7 
9*9 
1.9 
I Oats. 
1. 7 
3 * 9 
2. 1 
Com. 
2. 6 
7. 6 
1. 5 
Potatoes. .. 
4. 0 
10. 2 
2. 2 
Fallow.... 
i -5 
8*7 
1. 1 
The ammonifying powers of the soils are higher in summer than either 
spring or fall, and they are much higher in the fallow than in any of the 
cropped soils, the alfalfa being the lowest. In the fall the difference is 
not as marked, but even here the potato soil is the only one which has 
higher ammonifying powers than has the fallow. We thus find a close 
relationship between numbers and ammonifying powers of the soil. 
With the nitrifying powers we find no such regularity. Here the highest 
results are obtained with the potatoes, with the alfalfa a close second. 
Moreover, these results, if they represent what actually occurs in field 
conditions, indicate that the alfalfa must be removing the nitrogen 
from the soil much more rapidly than any of the other crops, for our 
previous results have taught us that the alfalfa is a close feeder upon the 
soluble nitric nitrogen- of the soil, and now we find alfalfa soil nitrifying 
the organic material to a greater extent than do the other soils. 
The low nitrifying powers of the oat soil is significant, as it indicates 
that the small quantities of nitric nitrogen found in this soil may be due 
in part to this factor. 
