Experiment Station Record, Volume 92, January-June, 1945 Page: 15
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drainage for 2 hr. on a sand flat), exceeded the field capacity by. an average value of
22.5 + 0.69 percent (volume basis),.
Two schedules of procedure are presented for measuring the physical properties
of soil samples collected in metal cylinders. Assuming that the soil to be investigated
is at its field moisture capacity, both schedules will result in essentially the
same values for field capacity (here taken as equivalent to water-holding capacity)
and volume weight. Values for pore volume will be highest, and presumably most
accurate, when the samples are treated according to one of the procedures in the
schedule in which the sample is removed from the cylinder and allowed to stand
in water for 24-48 hr., followed by boiling for 2 hr., and, finally, evacuation for 2-3
hr. "This treatment is very time-consuming and, for practical purposes, results in
values nearly the same as those obtained by the preferred procedure . . (as above,
but the samples are not boiled)." Samples receiving the latter treatment averaged
only 0.3 - 0.07 percent lower in pore volume than samples receiving the boiling
treatment. In a third treatment, the samples were neither boiled nor evacuated, but
the volume of the soil material was determined in a pycnometer. Pore volume determined
by this third treatment averaged 2.0 0.32 percent less than by the procedure
involving both boiling and evacuation. Results obtained by the procedure in
which cylinders with contained samples were allowed to stand in water 24-4.8 hr.,
and then weighed under water, indicate pore-volume values averaging 4.7 0.31
percent less than values obtained by both boiling and evacuation. Air-capacity values
bear an intimate relationship to pore-volume values. If the latter are too low, the
former will be correspondingly too low. On the other hand, if values for waterholding
capacity are too high, air-capacity values will be correspondingly too low.
It is further pointed out that removal of air from the sample in determining true
specific gravity may be incomplete, and true specific-gravity determinations carried
out in accordance with the procedure schedule not involving evacuation gave figures
averaging 0.21 0.01 lower than the values obtained in the schedule including evacuation
for from 2 to, 3 hr.
Soil development and plant nutrition.-II, Mineralogical and chemical composition
of sand and silt separates in relation to the growth and chemical composition
of soybeans, E. R. GRAHAM. (Mo. Expt. Sta.). (Soil Sci., 55 (1943),
No. 3, pp. 265-273).-The relation of the chemical composition of soybean plants,
grown on substrates containing sands and silts from various locations and subjected
to reaction with electrodialyzed acid clay, to the mineralogical and chemical
analyses of these soil separates, was investigated in a continuation of the work
previously noted (E. S. R., 89, p. 172).
No growth of the soybean plants could be obtained unless some calcium was
released from the sands and silts treated with hydrogen clay. Acid clay action on
silt and sand samples from certain locations made calcium, magnesium, and potassium
available; samples from other locations provided only calcium and magnesium;
other samples supplied only calcium; and still others gave no measureable
.amounts of any plant nutrients.
There were indications that phosphorus-bearing minerals, as measured by claymineral
interactions used, are rarely found in sands and silts. These coarser soil
separates may vary widely in calcium and quartz contents. Heavy feldspars were
present in significant amounts in the samples from Iowa, Utah, North Dakota, and
Kansas, and were almost absent from samples from Missouii, southern Illinois,
and Mississippi. Soil classification based on the mineralogical composition of sands
and silts is suggested as of help in considering soil productivity and soil needs for
calcium, magnesium, and potassium treatments.
Physical characteristics of soils.-IX, Relation between ultraclay and volume
of floc, A. N. PURI, B. RAI, and R. PAL (Soil Sci., 58 (1944), No. 2, pp. 163-175,
illus. 7).-A continuation of the series (E, S. R., 91, p. 643).
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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/m1/28/: accessed August 18, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.