I, 1924 
Movement of Water in Irrigated Soils 
663 
Mar. 
The soil used by Gedroiz in this experiment was rich in combined 
calcium and poor in sodium. When treated with a solution of sodium 
chlorid its chemical composition with respect to these bases was pro¬ 
foundly changed. It was observed also that its physical character was 
changed, but its characteristics with respect to permeability before and 
after treatment were not reported upon. 
Being already rich in calcium it would not be expected that the black 
earth with which Gedroiz worked would absorb much more calcium and 
thereby release other bases. The quantity of combined sodium which 
it contained was so small that there was very little of it to be replaced. 
In another experiment reported by the same author a sample of the 
same black earth was treated with a normal solution of calcium chlorid in 
the same way as described above for the treatment with sodium chlorid. 
The sodium was not determined in the second experiment, but the quan¬ 
tities of calcium, magnesium, and potassium extracted from the soil by 
10 per cent hydrochloric acid are reported in Table XXIII. 
Table XXIII. —Percentages of combined (not water soluble) bases in a sample of Russian 
black earth in its original condition and after being brought into equilibrium with a 
normal solution of calcium chlorid a 
Sample. 
Constituents soluble in 10 per cent 
hydrochloric acid in percentage of 
dry soil. 
CaO. 
MgO, 
KsO. 
Original soil. 
I. 36. 
I- 51 
•15 
O. 87 
.76 
O. 5a 
•49 
Treated soil. 
Absorbed. 
Replaced. 
. II 
•03 
« From Gedroiz. 
The results of these experiments show quantitatively the exchange 
reactions that may take place between the bases combined in the soil 
and those in solution in contact with the soil. 
The fact that such exchanges take place has been observed by several 
other investigators. It is obvious that such reactions take place in an 
irrigated field, as will be made apparent by comparing the composition 
of the irrigation water applied to a field and the drainage water discharged 
from it. 
THE COMBINED BASES AND PERMEABILITY 
In discussing the reactions of the basic elements that exist in the soil 
solution it is convenient to recognize two groups—the alkaline, which 
includes sodium, potassium, and ammonia, and the earthy, which in¬ 
cludes calcium, magnesium, iron, and aluminum. The elements of both 
groups may take part in exchange reactions between the solution and the 
soil. The effect of such reactions on the side of the soil is to produce one 
set of physical conditions when the combination is with the alkaline 
bases and a very different set of conditions when these are replaced by 
the earthy bases. 
These differences in the physical condition of the soil are manifested 
conspicuously in at least three ways—in permeability to water, in 
