300 
Journal of Agricultural Research 
XXIV, No. 4 
The crude culture proved to be most efficient in oxidizing sulphur in 
alkaline soil to such an extent that the reaction has been reduced, where 
sufficient sulphur has been used, from most alkaline to distinctly acid. 
This was accompanied by a complete disappearance of the carbonates, 
an almost complete disappearance of the bicarbonates, and an increase 
in the quantity of sulphates. With loo mgm. of sulphur per loo gm. of 
soil, equivalent to i ton of sulphur per acre (on the basis of the upper 
6 % inches of soil), 85 per cent of the sulphur has been oxidized by the 
crude culture to sulphates within 60 days, and the reaction reduced from 
Ph 9.6 to Ph 7.7. When the quantity of sulphur was doubled, prac¬ 
tically the same percentage of sulphur (85.5) was oxidized in 60 days 
and the Ph changed to 5.6 Where a large excess of sulphur was used, 
or 500 mgm. per 100 gm. of soil, only 44 per cent of the sulphur was 
oxidized to sulphate, and the reaction of the soil changed to Ph 4.7, 
which would already prove injurious to certain crops because of the 
excess acidity. The pure cultures did not prove quite as effective as the 
crude culture. This may be due to the fact that the oxidation of sul¬ 
phur in alkaline soil is carried out not by one organism but by several 
organisms taking part in the process, as is shown by the experiments 
reported in Table IV, where a mixture of the two organisms is used. 
The acid soil used in these experiments is a Sassafras sandy loam, slightly 
acid in reaction. These experiments were carried out both under sterile 
and nonsterile conditions in tumblers. 
Tables IV. —Oxidation of sulphur in acid and alkaline soils by pure and crude cultures 
of sulphur-oxidizing bacteria 
Soil type. 
Sterili¬ 
zation 
Organism. 
Incubated 
21 days. 
Incubated 
48 days. 
of soil.^ 
Ph 
fa 
■ + 
Control. 
6. 0 
5.8 
4. 4 
t. 8 
.do. 
c. 2 
+ 
Crude, acid compost. 
5 - 7 
4. 8 
.do. 
V 8 
Acid; 100 gm. of soil + 100 
mgm. of sulphur. 
Crude, alkaline compost.... 
.do. 
5-4 
c. 4 
5-0 
4.0 
5-0 
8 
+ 
Thiobacillus thiooxidans . 
.do. 
5-6 
+ 
Thiobacillus B . 
D ^ 
5.8 
5-4 
5-4 
4.8 
Q. 6 
q, 4 
.do. 
4. 0 
+ 
Thiobacillus thiooxidans + 
Thiobacillus B 
.do. 
3-4 
3 * 6 
' + 
Control. 
0 
0' 2 
.do. 
8. 8 
y 
8. 2 
+ 
Crude, acid compost. 
9. 0 
Q. 0 
8 2 
.do. 
8. 4 
+ 
Crude, alkali compost. 
y 
7 - 5 
7,6 
8. 8 
8. 2 
7 - I 
7 - 3 
8.6 
8. 0 
Alkali; 100 gm. of soil -f 
200 mgm. of sulphur. 
.do. 
+ 
Thiobacillus ihiooxidans . 
.do. 
+ 
Thiobacillus B . 
8. 2 
7. 8 
.do. 
8. 0 
7.6 
7. 6 
7. 4 
+ 
Thiobacillus thiooxidans + 
Thiobacillus B 
.do. 
7.8 
7. 6 
/ r 
1 + indicates that the flasks containing soil and sulphur were sterilized, at 15 pounds pressure, for 
hours: — =» soil unsterilized, in tumblers. 
