Mar. i, 1924 
Movement of Water in Irrigated Soils 
691 
The rate of the penetration of water into a dry soil is influenced not 
only by the general texture of the soil but even more by the physical 
reactions of the soil material to water. 
The addition of water to a dry soil causes a perceptible change in 
color, so that it is possible in the laboratory to observe and measure 
the rate of penetration and to establish the fact that the rate of pene¬ 
tration is very different in different soils. 
In a moist or saturated soil the movement of water, sometimes desig¬ 
nated as percolation, may also be measured with a fair degree of ac¬ 
curacy. • 
The physical condition of the soil, which influences so profoundly the 
movement of water through it, is largely the result of chemical reactions 
that take place between the soil particles and the salts dissolved in the 
soil solution. 
The character of the soil solution is a matter of fundamental import¬ 
ance in irrigated farming, not only because of its relation to the plant, 
but also because of its relation to the physical condition of the soil. 
It is difficult to estimate the normal concentration or composition of 
the soil solution from samples obtained by digesting the soil with an 
excess of water. 
The composition of the soil solution is determined by measuring its 
more important consitutents, which are identified as elements or ions and 
not as combined salts. 
The important constituents ordinarily identified in the soil solution 
of irrigated lands include the earthy bases, calcium and magnesium, 
also the acid ions, carbonate, bicarbonate, chlorin, sulphate, and nitrate. 
The alkaline bases, sodium and potassium, are not usually identified 
quantitatively, but are estimated by difference. 
The results of analyses of the soil solution may be stated in several ways, 
though for the sake of better understanding, it seems advisable to report 
only the constituents that have been identified. 
There are great differences in the solubility of the various constituents 
of the soil, and these solubilities are influenced to some extent by the 
composition of the soil solution. 
Changes in the concentration of the soil solution induce reactions 
between the solution and the soil, and consequently cause changes in the 
physical condition of the soil. 
Changes in concentration also result in changing the balance of the 
solution constituents in relation to each other. 
The soil solution is continually changing in concentration and in com¬ 
position, and the soil takes part in these changes through reactions 
between the basic constituents of the solution and the bases combined 
with the soil. 
The physical condition of the. soil and particularly its permeability to 
water is largely influenced by the character of the bases that are combined 
with the soil. When the alkaline bases, sodium and potassium, predom¬ 
inate the soil is deflocculated and impermeable. When the earthy bases, 
calcium and magnesium, are in excess the soil is flocculated and per¬ 
meable. 
When saline soils are leached to reduce the concentration of the soil 
solution it is often found that they become impermeable to water. This 
condition is due to the effect of the alkaline bases combined with the soil, 
which causes deflocculation to take place when the salts of the strong 
acids, sulphate and chlorin, are removed from the solution. 
