Mar. i, 1924 
Movement of Water in Irrigated Soils 
649 
soil. Under field conditions the soil solution is never at rest or in a condi¬ 
tion of equilibrium. During the time that irrigation water is being applied 
the solution is being diluted and is moving downward through the soil. 
For the remainder of the time it is being concentrated through the loss 
of water by evaporation and transpiration, and there may be a slight 
upward movement to replace these losses. In its movement the solution 
carries its dissolved substances with it. The movement of these dissolved 
substances by diffusion is probably so slight as to be negligible. For all 
practical purposes the movement of the dissolved salts in the soil is limited 
to and determined by the movement of the soil water. 9 
A solution constituent may be precipitated and its further movement 
arrested in either of two ways. The solution may become concentrated 
by evaporation to the point of saturation with respect to that constituent, 
or the constituent, if basic, may take part in an exchange reaction and 
be withdrawn from solution even though the solution is well below the 
saturation point with respect to it. It has not been demonstrated defi¬ 
nitely that the acid constituents of the soil solution take part in exchange 
reactions. 
There are very pronounced differences in the solubility of the various 
important constituents of the solution as it exists in irrigated soil. Very 
little is known as to what these limits are—that is, as to the concentrations 
at which the precipitation of any given salt takes place in the soil. The 
precipitation of a salt from solution or, in other words, the limit of 
solubility may be influenced profoundly by either of two factors. One 
of these is temperature and the other is the character of the other constit¬ 
uents in solution. The limits of solubility in pure water of the more 
important constituents of the soil solution in irrigated land are shown 
in Table XVII. The figures in this table give the limits of solubility in 
terms of percentage of the water of the solution and also in terms of the 
reacting values of the elements or ions. These figures show that with 
most of the salts the limit of solubility increases with the temperature. 
Table XVII .—Solubility in water of the earthy and alkaline bases in the presence of the 
various acids commonly found in the soil solution, expressed as percentage of the solvent 
and as reacting values a • 
Tempera¬ 
ture. 
Calcium Ca". 
Magnesium Mg". 
Sodium Na'. 
Potassium K'. 
Per 
cent. 
React¬ 
ing 
value. 
Per 
cent. 
React¬ 
ing 
value. 
Per 
cent. 
React¬ 
ing 
value. 
Per 
cent. 
React¬ 
ing 
value. 
Carbonate, C0 3 77 . . 
Bicarbonate, HCO3 7 
Sulphate, SO/ 7 .... 
Chlorin, Cl 7 . 
/ Cold... 
\Hot. . . 
/Cold... 
(Hot. . . 
0. 0013 
.088 
. 1 
0. 26 
17. 6 
20. 0 
0. 0106 
2-5 
7 - 1 
45-4 
6.9 
16. 4 
4. 8 
42.5 
35 - 7 
39 
72.9 
180. 0 
h 340 
8 , 57 ° 
821 
h 955 
656 
5 ? 9 00 
6, 100 
6, 660 
8,580 
21, 180 
89. 4 
156. 0 
22. 4 
60. 0 
8-5 
26. 2 
28.5 
56. 6 
* 3 * 3 
247.0 
12, 900 
22, 600 
2, 240 
6, 000 
975 
3,000 
3,825 
7 . 58 ° 
1 . 3*5 
24,400 
2. 21 
520 
/ Cold... 
\Hot. . . 
/Cold... 
\Hot. . . 
/Cold... 
\Hot. . . 
.179 
. 178 
59-5 
154 
93 * 1 
35 I- 2 
26.3 
26. 2 
IO, 725 
28, OOO 
”>356 
42, 829 
26. 9 
73 - 8 
S2. 2 
65-9 
200. O 
4 , 45 ° 
12, 200 
10, 950 
13; 850 
15, 620 
Nitrate, NO3 7 . 
1 
0 From Van Norstrand’s chemical annual, 1913 (20). 
* The movement of dissolved salts here referred to should not be confused with the movement of ions in 
the solution which may take place in connection with the absorption by plants. See Breazeale, J. F. (1) 
81990—24 - 3 
