298 
Journal of Agricultural Research 
Vol. XXIV, No. 4 
acid and alkaline soils. Two organisms have been isolated, which are 
responsible for this process. These two organisms are different in 
nature, in both their morphological and physiological characters: (i) 
Thiobacillus thiooxidans, isolated at this station from sulphur-soil com¬ 
posts and described in detail elsewhere (15), was found to be very active 
in oxidizing sulphur practically quantitatively in acid soils; and (2) 
Thiobacillus B was isolated from alkaline soils on which the sulphur had 
been actively oxidized. The organism resembles in general morphological 
and physiological characteristics T. thioparus, studied by Nathanson { 8 ) 
Beijerinck (j), and others, and occurs commonly in the soil. It grows 
readily in alkaline media having a reaction equivalent to Ph 9.8 and 
oxidizes readily thiosulphate witi an abundant formation of elementary 
sulphur. A detailed description of methods for the study of this organ¬ 
ism and its relation to the oxidation of sulphur in the soil are published 
elsewhere (r^). No definite proof can, however, be given that T. B is 
absolutely pure and not contaminated with T, thiooxidans or a related 
strain. 
In the experiment reported below, a black alkali soil from the 
University of California Ranch near Fresno, Calif., was used. Dr. 
Hoagland, of the University of California, who kindly supplied the soil, 
stated that “the physical condition of the soil was bad, the soil was 
extremely alkaline, and no ordinary growth of plants is supported.*’ 
The reaction of the soil was about Ph 9.6 to 9.8. 
The soil was placed in loo-gm. portions in tumblers and the proper 
amount of sulphur was added and thoroughly mixed with the soil. Fifty 
mgm. of sulphur in 100 gm. of soil is equivalent to 1,000 pounds of 
sulphur per i acre of soil (2,000,000 pounds per acre basis). The proper 
quantity of water was added and the tumblers were incubated at 25° to 
28° C. in the dark. 
The reaction of the soil was determined by shaking thoroughly 5 gm. 
of soil with 10 cc. of water, centrifuging, then determining the hydrogen- 
ion concentration (Ph value) colorimetrically and in some cases electro- 
metrically. The sulphates were determined by shaking the soil with 
distilled water (2) in a shaking machine for 2 to 6 hours, then filtering 
clear and precipitating as barium sulphate. The carbonates and bicar¬ 
bonates were determined by the method outlined by Schreiner and 
Failyer (jj). 
Tables I and II show the course of reaction resulting from the oxidation 
of sulphur in alkali soil and the chemical transformations that have taken 
place as a result of these changes. 
Table I .—Course of sulphur oxidation in alkali soil 
Period of incubation. , 
No 
sulphur 
added. 
50 mgm. 
sulphur 
per 100 
gm. soil. 
100 mgm. 
sulphur 
per 100 
gm. soil. 
200 mgm. 
sulphur 
per 100 
gm. soil. 
500 mgm. 
sulphur 
per 100 
gm. soil. 
1,000 mgm. 
sulphur 
per 100 
gm. soil. 
Ph 
Ph 
20 days. 
9. 6 
9.6 
9. I 
9.0 
8.9 
8.7 
42 days. 
9.6 
9*4 
9.0 
8.5 
7 - I 
6. 7 
62 days. 
9. 6 
9.4 
B.S 
7.8 
7. 6 
7.0 
86 days. 
9.6 
9-3 
8. 6 
8.0 
7.2 
6.8 
105 days. 
9. 6 
9. I 
7 - 9 
7. 2 
6. 0 
4.4 
167 days. 
9. 6 
7-9 
. 7.4 
6. 7 
5 * 7 
3 - 5 
