322
SOIL SCIENCE SOCIETY PROCEEDINGS 1961
Area
(g)}. The Cartesian manostat (c) maintains a constant vacuum
within the distribution tank (d), The magnitude of the distribution tank vacuum is indicated on the U-tube manometer (e@).
Six plates and associated collection carboys (figure 3) can
be simultaneously connected to the distribution tank. Leachate
passing into the carboy must first pass through a_ retaining
tube (¢) which has a volume of 50 mj. Thus, should the
vacuum fail, only the leachate in the retaining tube can be
siphoned back into the soil. The retaining tube also maintains
a constant water level in the carboy and effectively prevents
air from entering the tygon tubing (d) during short periods
of drought. During warm weather a film of transformer oil
is maimtained on the surface of the leachate to curtail
evaporation.
The exact tension placed against the plate is equal to the
vacuum within the collecting carboys minus the pressure
exerted by the column of water between the carboy and the
plate. Consequently, to maintain identical tensions against
plates located at various depths and connected to the same
distribution tank, the carboys must be placed at equal dis-
tances above their respective plates.
Analysis
Leachates were chemically analyzed in the following manner.
Nitrogen.—Nitrogen was determined as the ammonium,
nitrate and organic forms.
1. Ammonium nitrogen. An aliquot of the leachate was
made basic with MgO and distilled into 3% boric acid.
2. Nitrate nitrogen. The above aliquot was diluted to 500
ml., 2 g. of Devarda’s metal added, and slowly distilled
into boric acid. With leachates high in nitrate, it was
frequently necessary to redilute the aliquot and continue
the distillation for longer periods.
3. Organic nitrogen. Organic nitrogen was determined by
standard Kjeldal digestion after removing the ammonium
nitrogen by distillation as described above.
Calcium, potassium, phosphorus.—An aliquot of leachate
> 1 liter was evaporated to dryness and treated with 30%
H.O, until the residue was entirely white. This residue was
then redissolved into 10 ml. of 4N HCl, heated to 70° C.
for 2 hours, diluted to 50 ml., filtered, and then diluted to
100-ml. volume.
l. Calcium. A 1- to 5-m). aliquot of the above solution was
titrated with EDTA using murexide indicator.
2. Phosphorus. A 25-ml. aliquot was treated with 10 ml.
of ammonium vanadate solution and diluted to 50 ml.
The intensity of the resulting yellow color was determined
at 420 myz with a Klett-Summerson colorimeter.
3. Potassium. The solution was analyzed for potassium with
a Beckman Model D. U. flame spectrophotometer at
768 mz.
Lysimeters were installed in coral atoll soils at Rongclap
Atoll in the northern Marshall Islands and in glacial till soi
at Fern Lake in western Washington. In this way, two contrasting soil types were compared.
Parent material of the atoll soils is predominantly foraminiferal sand and coral sand and fragments transported by water
and wind to the land areas. Consequently, a recently deposited
soil is composed almost entirely of calcium and magnesium
carbonate, With the invasion of plant communities and subsequent deposition of organic material, a surface organic horizon
develops, changing such soil properties as cation-exchange
capacity, field moisture capacity, and the pH.
Mean annual temperature in the Marshall Islands is about
81° F. with little monthly deviation, and a diurnal variation
of 10° to 12°. The rainfall occurs primarily between April
and November during intense storms which frequently deposit
over 1 inch of precipitation. The annual rainfall is about 35
inches with wide annual variations (9).
The soils of Fern Lake originated from a glacial deposit.
The climate is moderate with a mean annual temperature of
about 50°
F. since the area is near sea level, adjacent to
Puget Sound. The average annual rainfall of about 46 inches
occurs primarily in the winter and spring months (14).
The general soil properties at the various lysimeter areas
are summarized as follows:
Lysimeter area 4, Middle Island coral soil—This soil is
frequently found im the relatively undisturbed center of the
island. Its fertility is exploited by the native population for
the cultivation of coconuts. This lysimeter area was located
adjacent to a coconut plantation in a Guettarda-Scaevola
thicket to avoid disturbance by native agricultural practices.
The soil surface Ao horizon is 1 to 11% inches thick underlain
by a very dark A; horizon extending to about 10 inches.
Beneath this horizon little organic matter is found and the
soil slowly merges into white sand at 40 inches. The soil pH
increased from 7.8 at the surface ta 9.0 at 40 inches while the
exchange capacity decreased from 20 to 1 me. per 100 g.
through the same depths.
Lysimeter area 5, Cordia, Pisonia coral soil—This soil is
the most fertile in the Rongelap area because of the numerous
birds nesting in the Pisonia trees. The surface Ao horizon is
1 to 1% inches thick and heavily matted with roots of
Boerhaavia, a low succulent ground cover. The A: horizon
extends to 6 inches and is followed by poorly sorted coral
fragments containing some organic material. At 24 inches the
coral is nearly white. The pH increased from 7.1 at the
surface to 8.6 at 20 inches.
The cation-exchange capacity
decreased from 43 to 2.6 me. per 100 g. through the same
epth.
Gamma-emitting radionuclides——The remaining leachate was
concentrated to < 25 ml. and the gamma-ray spectrum determined with a 3-inch sodium iodide crystal, thallium activated, used in conjunction with a 256-channel analyzer.
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Figure 2—Vacuum tank: (a) vacuum tank, 16 gauge stain-
less steel, 2 cu. ft. volume; (b) vacuum gauge for indicating when the tank needs re-evacuating; (c) Cartesian
manostat for maintaining a constant vacuum in the
distribution tank; (d) distribution tank, 18 gauge stain-
less steel; (e) V-tube manometer to measure the vacuum
in the distribution tank; (f) toggle valves, stainless steel
or brass, 13-inch pipe threads, to allow a series of plates
to be connected to a single tank; (g) toggle valve for
evacuating the air.
Figure 3—Leachate collecting carboy for use with the
vacuum tank: (a) connection to vacuum tank; (b, c)
tenite tubing, i-inch ID, 4-inch OD; (d) connection to
tension plate; (e) retaining tube, tenite, %-inch ID, %-inch
OD,6 inches long; (f) leachate.