17 
Table VII. — Showing effect of basicity on capillarity. 
K,HP04. 
KaPO*... 
Weight 
added. 
Gm. 
U.42 
1.92 
1.75 
Height. 
Cm. 
32.6 
30.3 
23.3 
KHjPOi 
KjHPO^ 
IC3PO4.. 
Weight 
added. 
Gm. 
0. 
Height. 
Cm. 
32.6 
30.9 
29.0 
1 Equivalent to 0.5 per cent K2O. 
The easily hydrolyzable salts, phosphates and carbonates of the 
alkalis, show the lowest water table. How^ever, they are much more 
active in organic soils due to their solvent action or chemical reaction 
with the organic matter present. These hydrolyzable salts also cause 
a swelling of the clay particles which, in Hawaiian soils, are partly 
composed of iron and aluminum hydrates and are conducive to the 
colloidal state, thus closing the pores, increasing friction, and lowering 
the rates of moisture rise. 
PERCOLATION. 
All moisture which passes below the surface, in excess of that held 
through capillary action or surface tension, is subject to the laws of 
gravity. The rate of movement, however, is dependent upon various 
factors, such as the size and composition of the soil particles, height 
of soil surface above water table, surface tension, and viscosity of 
the soil solution. 
Percolation is quite generally held to be most rapid in soils in 
which capillary activity is greatest, decreasing with height of column, 
and is faster in wet soils than in dry soils. Clay, of course, offers the 
greatest physical resistance to the passage of water and the resistance 
varies with the degree of aggregation of the clay particles. 
The rate with which water w^ill pass downward, then, depends upon 
the physical state of the soil and this in turn varies with the arrange- 
ment of the soil particles. Both of these properties, however, are 
affected by the nature of the soil solution, percolation decreasing 
with increase in concentration. 
For studying the effect of fertilizers upon this property of soils 
1-inch glass tubes containing soil columns of about 30 centimeters 
were fitted up as in studying the capillary activity. These tubes 
were connected with a constant supply reservoir which maintained 
a 1-inch head of water in the tubes, and the water passing through 
the soil was measured at intervals. The totals of these measure- 
ments are given in Table VIII. 
