294 
Journal of Agricultural Research 
Vol. XXIV. No. 4 
TabI/IS V .—Effect of basic compounds upon the longevity of Azotobacter in an acid soil ( 7 )® 
Sample 
No. 
Basic compounds added. 
Pounds 
per acre, ft 
Ph. 
Azotobacter cultures. 
Eeb. 10. 
Mar. 19. 
May 8. 
I 
0. 01 per cent CaCOg. 
300 
59 
-f 
4- 
2 
. 05 per cent CaCOg. 
I, 500 
6. 0 
4- 
+ 
— 
3 
. 10 per cent CaCOg. 
3)000 
6. 2 
4- 
4- 
4- 
4 
. 50 per cent CaCOg. 
15,000 
7*4 
4- 
4- 
4- 
5 
I. 00 per cent CaCOg. 
30, 000 
7-4 
4- 
4- 
4- 
6 
2. 50 per cent CaCOg. 
75, 000 
7-4 
+ 
4- 
4- 
7 
. 01 per cent Na^COg. 
300 
S.8 
-f 
4- 
— 
8 
. 05 per cent Na2COg. 
1,500 
6. 0 
-h 
4- 
+ 
9 
. 10 per cent Na2COg. 
3,000 
6. 2 
+ 
4- 
4- 
10 
. 50 per cent Na2C03. 
15,000 
7.6 
4- 
+ 
+ 
II 
I. 00 per cent Na2COg. 
30, 000 
C8.6 
4- 
+ 
4- 
12 
2. 50 per cent Na2COg . 
75,000 
c8. 6 
4- 
— 
■ — 
13 
. 01 per cent Mg.COg . 
300 
5.8 
4- 
4- 
— 
14 
. 05 per cent Mg.COg . 
I, 500 
6. 0 
4- 
4- 
4- 
15 
. 10 per cent Mg.COg . 
3,000 
6.4 
4- 
4- 
4- 
16 
. 50 per cent Mg.COg . 
15,000 
7.6 
4- 
+ 
+ 
17 
I. 00 per cent Mg.COg . 
30,000 
8.0 
+ 
+ 
+ 
18 
2. 50 per cent Mg.COg . 
75, 000 
8.6 
4- 
+ 
o -f =* Presence of Azotobacter. — = Absence of Azotobacter. Experiment set up Jan. 21 , Moisture 
content optimum. Acidity determined colorimetrically. 
^ 3 , 000,000 pounds soil, 
c Greater than 8 . 6 . 
It is evident from the data presented in Tables III, IV, and V that 
the addition of calcium carbonate to an acid soil, not containing Azoto¬ 
bacter, if in sufficient quantity to reduce the hydrogen-ion concentration 
to approximately Ph 6.0 or lower, is all that is necessary to render the 
soil capable of supporting an Azotobacter flora. In no case, however, 
have Azotobacter been observed to appear in a soil so treated unless 
accompanied by inoculation either natural or artificial. In other words, 
Azotobacter are actually not present and must be introduced or the addi¬ 
tion of calcium carbonate can have no effect upon nitrogen fixation by 
this group of organisms. 
* EFFECT OF ADDING ACID 
In the experiments reported in Tables VI and VII, increasing quanti¬ 
ties of various acids were added to soils A and C. Both these soils con¬ 
tained abundant Azotobacter. The reaction of soil A was very near 
Ph 7.0 and of soil C was near Ph 6.5. 
Sulphuric, hydrochloric, acetic, and butyric acids were added to soil 
C reported in Table VI. Sulphuric and hydrochloric acid increased the 
hydrogen-ion concentration of the soil as the quantity of acid increased. 
As soon as the acidity passed much beyond Ph 6.0 Azotobacter were 
unable to survive prolonged incubation. When acetic or butyric acid 
was added it apparently had no effect upon the reaction, unless to re¬ 
duce the hydrogen-ion concentration. This is contrary to the data 
presented in Table VII and is probably due to the time at which the 
hydrogen-ion concentration determinations were made. In Table VI 
the reaction was determined at the end of the period of incubation, 
while in Table VII the acidity determinations were made immediately 
