334 Journal of Agricultural Research voi. ix, no 9 
the potato soil is only slightly lower than the quantity produced in the 
fallow, while the corn shows a slight decrease below the potato soil. As 
has been the tendency throughout each series, the ammonifying powers 
decrease considerably in the fall, and this decrease is greater in the fallow 
than in any of the cropped soils. 
Here for the first time the fallow soil has a higher nitrifying power 
than the alfalfa soil. This is due to the difference in moisture content 
of the soil, for the unirrigated alfalfa plot became very dry during the 
summer and fall, while the fallow remained moist throughout the year. 
The very high nitrifying power of the potato soil is shown again in this 
series, making it certain that this is not due to accident but is charac¬ 
teristic of the potato plot. 
The influence of crop upon the bacterial activities of the soil is empha¬ 
sized in the result given in Table XXXIII, in which we have the average 
from all the plots receiving the different amounts of water. 
Table XXXIII. — Average bacterial activity of the soil as influenced by crop 
NUMBER OF BACTERIAL COLONIES DEVELOPING IN 4 DAYS ON SYNTHETIC AGAR 
Crop. 
Sampled 
May 1 . 
Sampled 
Aug. 1 . 
Sampled 
Nov. 28. 
Average. 
Alfalfa. 
8,308, OOO 
6,392, 000 
5,833,000 
5, 900,000 
4, 883, OOO 
6,600, 000 
5, 492, OOO 
5,666, 000 
6, 083,000 
4 , 475 > 000 
4 , 5°°, OOO 
4 , 349> OOO 
3, 608, OOO 
4 , 792,000 
2, 550, OOO 
6,469; OOO 
5,411,000 
5, 035, OOO 
5, 591,000 
3>969,000 
Oats. 
Com. 
Potatoes. 
Fallow.. 
MILLIGRAMS OP AMMONIA PRODUCED IN IOO GM. OF SOIL IN 4 DAYS 
Alfalfa... 
50-9 
S a 7 
4a 1 
47. 2 
Oats. 
5 1 - 7 
57-8 
48.1 
S 2 . 5 
Com... 
52.8 
58-4 
45 - 2 
52.1 
Potatoes. 
55 - 2 
64. 2 
47.9 
55 - 7 
Fallow. 
63-9 
73 -o 
Si-2 
62. 7 
MILLIGRAMS OF NITRIC NITROGEN PRODUCED IN IOO GM. OF SOIL IN 21 DAYS 
Alfalfa. 
3-15 
7.48 
3*08 
4 - $6 
Oats. 
2. 40 
4. 00 
3.00 
3 -13 
Com. 
2. 18 
3 - 50 
1. 48 
2.38 
Potatoes. 
3.00 
i 5 - 55 
5- 60 
8. 04 
Fallow. 
1. 30 
5 - 5 ° 
2. 48 
3*€>9 
The most marked characteristic of all these results is that they are 
extremely low when compared with the results obtained on other soils, 
thus showing that the limiting factor is organic matter. The number of 
organisms is highest in the alfalfa and lowest in the fallow; and, with the 
