Mar. x, 1924 
Movement of Water in Irrigated Soils 
639 
Table XI.— Salt content of the solution and the indicated salt content of the soil when 
the soil solution was variously diluted —Continued. 
Sample No. 
Percentage 
of solution 
to soil. 
Salt content 
of solution. 
Indicated 
salt content 
of soil. 
Per cent ., 
Per cent. 
33 
. 062 
. 020 
47 
. 070 
•033 
386. 
100 
•035 
• 035 
250 
. 019 
. 048 
500 
. 012 
. 061 
1, 000 
. 008 
. 080 
30 
2. 200 
. 660 
46 
I. 510 
. 694 
100 
.665 
. 665 
250 
. 262 
•655 
500 
. 130 
. 650 
1, 000 
. 066 
.660 
The outstanding features of Table XI are that these soils not only 
differ greatly in their percentages of soluble material but they differ also 
with respect to the solubility of that material. 
In the case of soil No. 384 the indicated salt content is substantially 
the same when computed from the centrifuge extract as when computed 
from the extracts made with large quantities of water. The same is 
true with soil No. 385a. 
With the other two samples, the results are different. With them the 
indicated salt content of the soil is very much higher when an excess of 
water is used than when the solution is nearer the normal of field condi¬ 
tions. 
These examples are given here to show why it is that investigators 
hesitate to estimate the concentration of the soil solution from the 
results they obtain by testing dilute water extracts of the soil. 
COMPOSITION OF THE SOIL SOLUTION 
Most investigators who are working with solutions obtained from 
irrigated soils do not attempt to identify all of the substances contained 
in these solutions. Many of the dissolved materials occur in very minute 
quantities, and it is probable that they do not have much effect either on 
the soil or on the plants. There is a wide diversity in the methods used 
by different workers in the examinations of soil solutions, a term which 
is here used to include not only the water extracts from soil samples but 
irrigation and drainage waters as well. 
Even in estimating the total quantity of dissolved material there are 
differences of method. A few of the methods in general use may be 
listed and briefly described as follows: 
(1) A measured quantity of the solution is evaporated to dryness over a steam bath 
and then dried to constant weight in an oven at a temperature slightly above the boiling 
point of water; the dried residue is weighed and reported as total dissolved solids in 
terms of percentage of the original solution or in parts per million. 
(2) The same as No. 1 except that the residue after being weighed is heated to low 
redness to volatilize the organic matter and then weighed again. The loss in weight 
from heating is then reported as organic matter, and the final residue is reported as 
total salts. 
