Experiment Station Record, Volume 92, January-June, 1945 Page: 16
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16 EXPERIMENT STATION RECORD [Vol. 92
A 1-percent soil suspension was prepared, after maximum dispersion by the
HCl-NaOH method, and clay was pipetted off in the usual way. Four cc. of the
clay suspension was put in a measuring tube, 1 cc. of 0.25 N CaCl2 solution was
added, and the suspension was centrifuged for 0.5 hr. The volume of the settled
mass was read directly from the measuring tube, which was calibrated accurately
up to 0.01 cc. The floc volume described is shown to depend on the particle
size in the ultraclay range. The percentages of various ultraclay fractions present
in a soil could be determined by measuring the floc volume of the soil. Variations
in pH value and in time of aging are shown to affect the floc volume as well as
the proportion of ultraclay.
Hydrogen-ion concentration of the important soils of the United States in
relation to other profile characteristics.-I, Pedocal soils, E. H. BAILEY.
(U. S. D. A.). (Soil Sci., 57 (1944), No. 6, pp. 443-474, illus. 1).-The soils here
dealt with are confined to those of the Pedocal classification. H-ion determinations
were made in duplicate with a hydrogen electrode on samples of each of the
horizons of several carefully selected profiles of a considerable number of important
soil series in the United States. These series are classified into the various
great soil groups. Every profile studied is located on a great soil group association
map of the United States.
The lime zones of the Pedocal profiles range from mildly alkaline to very
strongly alkaline in reaction. In the grassland Pedocals, such as the Chernozem,
Chestnut, reddish Chestnut, Brown, and reddish Brown soils, the horizons above
the lime zones have virtually the same reaction range-medium-acid to strongly
alkaline. In the Desert and Red Desert profiles, the horizons above the lime
zones have virtually the same reactions as the lime zones. In the Sierozem profiles,
the horizons above the lime zones tend to be more alkaline than those of the grassland
Pedocals but not so alkaline as those of the two Desert groups. They are
neutral to strongly alkaline.
The effect of soil physical conditions on moisture constants in the upper
capillary range, W. O. SMITH. (U. S. D. A.). (Soil Sci., 58 (1944), No. 1, pp. 116,
illus. 4).-The author discusses soil moisture constants in the upper capillary
range from the standpoint of soil physical conditions, presenting some evidence to
indicate that, at moisture equivalent, the water of a heavy soil which does not swell
appreciably is largely contained in the textural pore space. At this moisture point,
the textural pore space is held to be saturated, or nearly so. Conditions prevailing
in a sand at moisture equivalent are quite different. The pore space is not usually
saturated. Formulas for calculating the porosity of a heavy soil from its moisture
equivalent and volume-weight or from its moisture equivalent and the density of its
solids are given.
The conclusions "are based on limited data, and extensive study probably must be
made to establish with certainty the behavior here postulated." Soil physical conditions,
important in transfer processes such as the passage of heat or water, must also
be considered when such moisture constants of the upper capillary range as moisture
equivalent, field capacity, and normal moisture capacity are measured or used.
The dependence of field capacity upon the depth of wetting of field soils,
E. A. COLMAN. (U. S. D. A.). (Soil Sci., 58 (1944), No. 1, pp. 43-50, illus. 6).A
determination of field capacity by natural and artificial irrigation of mountain
soils in situ and of a mixed, uniform soil has shown that these soils must be wetted
12-30 in. deep, the depth depending on the soil studied, before the surface layer will
have attained a moisture content as high as its field capacity. Subsurface layers are
shown to have lesser wetting zone thicknesses, but soil as deep as 30 in. is not raised
to its maximum moisture until the wet front has penetrated from 36 to 42 in. below
the soil surface. A tentative explanation relates the field-capacity values to the
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U.S. Department of Agriculture. Agricultural Research Administration. Office of Experiment Stations. Experiment Station Record, Volume 92, January-June, 1945, book, 1947; Washington D.C.. (digital.library.unt.edu/ark:/67531/metadc5064/m1/29/: accessed July 27, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.