460 
Journal of Agricultural Research 
Vol. V, No. it 
organisms upon which the plants rely for their available nitrogen, pro¬ 
vided proper soil texture is maintained. 
Furthermore, it was found that in time the arsenic practically loses 
its toxic influence toward plants. This was shown by the comparative 
growth of plants on soils treated at time of seeding and those seeded 
several months following the application of the arsenic to the spil. There 
are only two possible explanations of this condition: Either the arsenic 
reacts with certain of the soil constituents, resulting in a less toxic 
combination, or it is rapidly leached from the soil. 
ABSORPTION OF ARSENIC BY THE SOIL 
When a soluble salt is added to a soil, its ultimate disposition must 
depend upon certain chemical reactions and physical phenomena. In 
this case the possibilities involve (1) a combination with or replace¬ 
ment of salts already present, resulting in its absorption as a whole; or 
(2) a selective absorption involving the fixation of only one ion of the salt. 
In order to determine the fate of arsenic and the effect of irrigation, 
a set of lysimeter experiments was inaugurated. 
LYSIMETER EXPERIMENTS 
Three types of soil were selected: (1) A ferruginous red clay, (2) a 
ferruginous brown clay, and (3) a highly organic silt. Twenty-five 
pounds of soil were placed in each of six lysimeters, two being filled with 
each type. To each soil were added 3 liters of a solution of sodium 
arsenite of the same strength as that used for spraying weeds. One 
series of three was allowed to stand for two months protected from 
rain. To the other three 1 liter of water was added every other day 
for several weeks, after which the soil was allowed to stand in the lysim¬ 
eter until dry enough to sample. 
The object of these experiments was to determine the rate of fixation, 
the depth to which the arsenic can penetrate, and the leaching effect of 
irrigation. At the expiration of the above time samples were taken 
at various depths in the lysimeters and the percentage of arsenic (As 3 0 3 ) 
in the soil at each depth was determined. The results are given in 
Table I. 
Table I .—Effect of irrigation on arsenic in the soil, giving the percentage of arsenic at 
various depths 
Soil No. 1. 
Soil No. a. 
Soil No. 3. 
Depth. 
Not irri¬ 
gated. 
Irrigated. 
Depth. 
Not irri¬ 
gated. 
Irrigated. 
Depth. 
Not irri¬ 
gated. 
Irrigated. 
Inches. 
Per cent. 
Per cent. 
Inches. 
Per cent. 
Per cent. 
Inches. 
Per cent. 
Per cent. 
1 to 3 
0. 280 
O. 224 
1 to 3 
O. 450 
O.237 
I tO 2 
O. 97 
0. 95 
3 to 5 
. 198 
'. 211 
3 to 5 
. 170 
. 092 
2 tO 4 
• So 
•47 
Sto 7 
. 171 
• 145 
5 to 7 
. 118 
. 092 
4 to 6 
0 
O 
7 to 9 
. 184 
. 170 
7 to 9 
.013 
