322 
Journal of Agricultural Research 
Vol. IX, No. 9 
Table XXII. —Number of colonies of bacteria , milligrams of ammonia , and milligrams 
of nitric nitrogen from soil receiving varying amounts of water. Crop , alfalfa . A verage 
for three years 
NUMBER OR COLONIES OF BACTERIA DEVELOPED IN 4 DAYS ON SYNTHETIC AGAR PER 
GRAM OF SOIL 
Plot No. 
Water 
applied. 
Sampled 
May 1 . 
Sampled 
Aug. 1 . 
Sampled 
Nov. 28 . 
Average. 
31. 
Inches . 
37- 5 
6, 700, OOO 
6, 433 ? 000 
2, 800, OOO 
5,311,000 
32. 
25.0 
8, 933, 000 
9, 466, OOO 
7, 066, OOO 
6, 566, 000 
4,933, OOO 
6,977,000 
6,877,000 
33. 
15. 0 
4,600, OOO 
5,667,000 
34. 
None. 
8,133,000 
333.000 
6,711,000 
MILLIGRAMS OF 
AMMONIA PRODUCED 
IN IOO GM. OF SOIL IN 4 
DAYS 
31. 
37- 5 
50.5 
46. O 
42. 2 
46. 2 
32.. 
25.0 
49-9 
51*2 
39* 0 
46. 7 
33. 
i5- 0 
5 i *9 
52.8 
35*2 
46. 6 
34. 
None. 
53*5 
52.7 
43* 0 
49*7 
MILLIGRAMS OF NITRIC NITROGEN PRODUCED IN IOO GM. OF SOIL IN 21 DAYS 
3i. 
37-5 
3*7 
9*9 
i*9 
5*2 
32. 
25.0 
2 . 7 
8 . 6 
3*7 
5*o 
33. 
i5* 0 
4- 7 
5*2 
3*6 
4- 5 
34. 
None. 
i*5 
6 . 2 
3* 1 
3*6 
The number of organisms in this soil which develop on synthetic agar 
is greater in May than in August or November. In all the plots there 
was a gradual decrease from spring to fall. This difference is greatest 
in those plots which received the most water. The number of organisms 
is greatest in the soil which received no water and least in the soil which 
received 37.5 inches of water. In every instance during spring and fall 
the number of organisms decreases as the water applied increases; and 
the difference is so marked and regular that it seems safe to attribute 
it to the water applied. During the summer the difference in the num¬ 
ber of organisms in the various plots is not great; especially is this true 
in the irrigated plots. 
The ammonifying powers of all the soils are highest in spring and 
lowest in fall. The difference in the quantity of ammonia produced in 
the various soils is not great. But during the spring and summer the 
ammonifying powers of each soil decrease as the water applied increases. 
The difference is not regular in the fall; but from all the results it seems 
quite certain that the addition of irrigation water to alfalfa soil, such as 
used in this investigation, causes a decrease in the ammonifying powers 
of the same. 
The nitrifying powers of all the soils are higher in midsummer and lower 
in the fall and spring. This difference is very pronounced in the soil 
