Apr. 9,1917 
Water-Retaining Capacity of Soil 
69 
the section adjacent to the surface of application, where it lay between 
1.7 and 2.4. The ratio, while falling within these limits, is not a con¬ 
stant, it not being the same for all the soils that have the same hygro¬ 
scopic coefficient. 
The water-retaining capacity of the loams, as determined by labora¬ 
tory experiments, was found to bear a somewhat closer relation to the 
moisture equivalent than to the hygroscopic coefficient, the ratio varying 
between 0.8 and 1.2. 
Coarse sands exhibited a behavior very different from that of the 
loams. The ratio in the surface 6-inch section, even three months after 
1 inch of water had been applied to the surface, was as high as 6.0 or 
7.0, while in the second foot it was only 1.0. The field studies on coarse 
sands showed as high a final ratio as was observed in the laboratory 
experiments. 
The very limited studies on fine sands indicate that these occupy a 
position intermediate between the loams and the coarse sands, the ratio 
of the water-retaining capacity to the hygroscopic coefficient rising as 
the latter value falls. 
Field studies show that when loams, after rains sufficiently heavy to 
moisten them thoroughly, are protected from losses by evaporation 
and transpiration, they lose water by downward movement until the 
ratio of moisture content to hygroscopic coefficient lies between 1.8 and 
about 2.5, and accordingly on the uplands of dry-land regions this is 
the ratio to be expected in the deeper subsoil—the portion below the 
range of plant roots. 
A comparatively abrupt transition from the moistened soil to the thor¬ 
oughly exhausted underlying layers, with ratios of 2 to 2.5 and 1.0 to 
1.1, respectively, is found even several months after liberal rains have 
fallen, if the subsoil to a considerable depth had previously been ex¬ 
hausted of available water. 
The moisture of the deeper subsoil will be able to move upward only 
so slowly and through such a short distance in a single season that it will 
be at most of no practical benefit to annual crops. To make use of any 
portion of the precipitation which penetrates beyond the reach of the 
roots of annual crops it will be necessary to follow such crops at intervals 
by deep-rooting perennials. 
Further experiments of a long-time character are necessary to decide 
definitely whether the deep subsoil may not in a decade or so contribute 
sufficient moisture to the subsoil within the reach of the roots of such 
perennials, 20 to 30 feet, to make such a contribution of some practical 
importance for such crops. 
