Apr. 28, 1923 
Oxidation of Sulphur in Black Alkali Soils 
301 
In the acid soil, oxidation of sulphur took plac^ in the unsterilized 
containers whether inoculated or uninoculated, more so in the inoculated 
cultures, particularly where the Thiobacillus thiooxidans was introduced. 
This is due to the fact that the sulphin added, in nonsterile condition, 
probably has been inoculated previously from the laboratory air. 
However, when the soil and the sulphur are previously sterilized, oxi¬ 
dation takes place only to a very unappreciable extent, unless the proper 
sulphur-oxidizing organisms are introduced. In the alkaline soil, the 
most efficient results were obtained from inoculation with the crude 
alkaline culture, or alkaline soil, in which sulphur oxidation had taken 
place previously. The pure cultures, particularly the Thiobacillus B 
culture, which was almost inactive in the acid (sterilized) soil, proved 
more efficacious than the T. thiooxidans; but a mixture of the two 
cultures proved nearly as efficacious as the crude alkaline composts. 
The fact that the change of the soil carbonates to sulphates would 
also favor plant growth, which is found to be so in actual field results, 
was demonstrated in these experiments by the increase in the number 
of bacteria developing in the soil. The soils used in the experiment 
reported in Tables I and II were at the end of the experiment air dried, 
then again moistened and, after 5 to 6 days, the bacterial numbers were 
determined by the ordinary plate method. The alkali soil, to which 
no sulphur had been added, contained 320,000 bacteria per gram of 
soil; where 50 mgm. of sulphur had been added per 100 gm. of soil 
and the reaction changed to Ph 7.9, there were 665,000 bacteria per 
gram; 100 mgm. of sulphur, reaction Ph 7.4, 875,000; 200 mgm. of 
sulphur, reaction Ph 6.7, 1,275,000; 500 mgm. of sulphur, reaction P^ 
5-7> 3,650,000; 1,000 mgm. of sulphur, reaction Ph 3.5, no bacteria, 
only a few occasional fungi. In this case, the soil reaction has been 
made so acid as to completely kill off tjie bacteria. This danger, how¬ 
ever, could hardly be expected in the field, because no such large quan¬ 
tities of sulphur (i per cent) would ever be employed. 
In the following experiment, the reaction of the soil was adjusted by 
the addition of sulphuric acid and sodium carbonate. The following 
amounts of acid and alkali were used to adjust the reaction of the soil : 
Untreated soil. 
5 cc. NI2 Ho SO4 per 100 gm. of soil— 
0.5 cc. M/2 NajCOs per 100 gm. of soil. 
i.o cc. MI2 NagCOa per 100 gm. of soil., 
3.0 cc. M/2 NagCOg per 100 gm. of soil., 
7.0 cc. MI2 NajCOg per 100 gm. of soil. 
20.0 cc. M/2 NajCOg per 100 gm. of soil 
Ph. 
5-6 
5-3 
5.8 
6. o 
6. 2 
6.4 
8.4 
One-gm. portions of powdered sulphur were added to each loo-gm. 
portion of soil in Erlenmeyer flasks; the flasks were well shaken, plugged 
with cotton, sterilized at 15 pounds pressure for 1% hours, then inoculated 
with pure cultures^of the organisms and incubated at 25^0. At the end 
of definite intervals of time the moisture content was brought up by 
the addition of sterile distilled water. The results are presented in 
Table V. 
