The Relation of Subfur to Soil Fertility. 623
These results also show why the plants in Nos. 2 and 3 did
not make any growth since the soil probably became acid
by the large amounts of sulfur oxidized. On the other hand,
the plants grew well in   6 and 7 because calcium carbon-
ate had been added. /.
TEXPERIMENT fl.
_ The soil to which sulfur had been added in Series V was
used for the follow`ng experiments:
Table XII-—Oxidatf1 of Sulfur to Sulfur Trioxide in Soil of Series V.
Box Per cent Sulfate Sulfur. Per cent
,————-—-- ——— Sulfur
At the After Oxidized
_ begin- 112
¤ ning. days.
No. 15 100llbs. sulfur per A. .016 .020 80
“ 16 500. " " " " .016 .033 68
“ 17 1000 " " " " .017 .047 60
“ 18 2000 “` " “ " .019 .086 67
· “ 19 3000 " " " “ .020 .111 61
“ 20 5000 " " " “ .023 .181 63
" 21 7000 " " “' “ .025 .285 74
" 22a No sulfur added .016 .016
“ 22b “ " " .016 .017
These results show that from 60 to 80 per cent of the
sulfur, regardless of the amount added, was oxidized after a
period of about four months. This also holds true whether the
soil was only slightly or decidedly acid, for acidity tests
which were made at the same time and which have been
previously mentioned, showed that the soil in Nos. 19, 20
and 21 was decidedly acid and the acidity increased as the
amounts of sulfur became larger. In these boxes, the plants
did not grow and most of them died.
If the different amounts of calcium carbonate calculated
from the sulfuric acid that was formed by the oxidation of
the sulfur in the soil above, are compared with the quanti-
l _ ties required by the Hopkins acidity determinations pre-
viously mentioned, and then with the amount that was
originally added, some interesting relations are shown to V
exist, as will be seen in the following table: