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Jül - 514 - LW
KERNFORSCHUNGSANLAGE JOLICH GESELLSCHAFT MIT BESCHRÄNKTER HAFTUNG
Institut für Landwirtschaft
Studies on tagged clay migration
due to water movement
H. W Scharpenseel and W. Kerpen -
Als Manuskript gedruckt
Berichte der Kern forsch u n g so n 1 o g e J ü 1 ich - Nr. 514 Institut für Landwirtschaft Jül - 514 - LW
Dok.: Soils - Clay Migration Clays - Tracer T echniques
DK: 631.41 :552.52:574.91 552.52: 621.039.85
Zu beziehen durch: ZENTRALBIBLIOTHEK der Kernforschungsanlage Jülich, Jülich, Bundesrepublik Deutschland
Reprint f rom
''ISOTOPE AND RADIATION TECHNIQUES
IN SOIL PHYSICS AND IRRIGATION STUDIES"
INTERNATIONAL ATOMIC ENERGY AGENCY
STUDIES ON TAGGED CLAY MIGRATION DUE TO WATER MOVEMENT
H. W. r§._CHARPENSEEL INSTITUT FÜR BODENKUNDE DER UNIVERSITÄT BONN, AND W. KERPEN ARBEITSGRUPPE, INSTITUT FÜR LANDWIRTSCHAFT DER KFA JÜLICH, FEDERAL REPUBLIC OF GERMANY
STUDIES ON TAGGED CLAY MIGRATION DUE TO WATER MOVEMENT. 55 Fe-tagged clay minerals, produced by hydrothermal synthesis, serve to clarify the question whether clay migration or clay formation in situ is the predominating mechanism in the Bcdevelopment of Parabraunerde (sol brun lessive, grey brown podsolic, hapludalf, demopodsol). They further indicate the possibilities of clay transportation caused by water percolation. Suitable experimental approaches, such as thin-layer chromatography and autoradiography. translocation tests in columns filled with monotypical textural fractions or with undisturbed soil profiles, and synchronous hydrothermal treatment of 5iöpe-containing material from different horizons of Parabraunerde, to reveal the specific readiness of the different _profile zones for 55Fe-clay production, are described. The possibilities of clay percolation are discussed.
Although clay migration is traditionally considered to be the valid explanation for the phenomenon of horizons of clay accumulation, such as that in argids, alfisols and ultisols, this assumption is based on indirect evidence arising from the textural comparison of the horizons and micro- morphological thin- slide demonstration of plasmatic flow structures.
While the movement is certainly too slow to be detected by direct observation, one could expect to confirm or refute the clay migration concept from: ( 1) Model experiments with columns of undisturbed soil profiles, or of
different textural composition; (2) Thin- layer chromatographic tests with layers of different grain- sizes; (3) Trials to detect in- situ clay formation in the accumulation horizon as
proof of an alternative mechanism; (4) Chemical and physical comparison of the clay minerals in the A 1- and
A1 -horizon with those along the plasmatic flow structures. The methods connected with (1) - (3) require the use of tagged clay,
which is distinguished by its radiation from the resident clay and mineral substance.
In earlier reports [1, 2) the production of 55Fe-labelled kaolinite and montmorillonite by hydrothermal synthesis in high-pressure autoclaves were explained.
A comparison of the constituents taking part in the synthesis of the clay minerals montmorillonite and kaolinite, with the partial substitution of 55Fe in isomorphic exchange for aluminium, is given in Table 1.
1. COLUMN EXPERIMENTS
In studying tagged clay migration, the approach that is closest to natural field conditions is to administer 55Fe-tagged clay, placed in
280 SCHARPENSEEL and KERPEN
T ABLE I. CONSTITUENTS IN THE SYNTHESIS OF MONTMORILLONITE AND KAOLINITE
672. 7 mg
Alp 3 214. 9 mg
Mg-acetate 396 mg
KCl 68. 9 mg
55 Fe (OH) 3
HP 71 ml
Treatment 14 d, 300°C, 80 atm, or 42 d, 225°C, 50 atm.
Autoclave 205 ml.
1= ... l=o=
' „. ' ~· . „ ' . - . ~
'u'« ~ 'v'* ~ „~ - - ~ - ~ I / = =~ ~
/ / ........ -- ~ ..:~ ,/' - - -~=' I~ 1 1 t •I V//ll/!1 (///l/il 1YXIX K.'1!//l!(h '/////;'u //~
v ~- --- FIG. l. Columns with well-defined soil texture-fractions; conternporary percolation by rneans of a dosis pump.
1.50-m-long glass columns, in the upper zone of undisturbed soil profiles. By perfusion with known, sufficiently large amounts of water, and by activity scanning, the potential clay movement can be observed (3, 4]. Results so far obtained show little evidence of a clay migration, but rather an immobile storage of the tagged clay in a layer near the surface.
Since such experiments have not yet confirmed a measurable clay migration, a second perfusion method, in 50-cm columns filled with well- defined textural soil fractions, was carried out (Fig. 1).
The following fractions were singled out with the aid of sedimentation cylinders:
0 .002 - 0.02 mm diam. 0.02 - 0.06 mm diam. 0.06 - 0.2 mm diam. 0.2 - 1 mm diam.
- 2 mm diam.
Incorporated in the upper 1- cm layer of the five columns were 150 mg of 55Fe - labelled montmorillonite with 6000 dpm/mg, suspended by ultrasonic treatment in 0.4_!'i sodium pyrophosphate . Each percolation amounted to 1000 ml, equivalent to about 10000-mm precipitations. A thin inner coating of the columns with silicon oil prevents the water from forming preferential flow tracks along the glass walls. After the percolation the collected water was agitated and aliquots were tested for their activity. The activity rate in the liquid- scintillation spectrometer, minus the back- ground (slightly increased), would express quantitatively the extent of eluted tagged clay.
FIG. 2. Thin-layer chromatographs with 55Fe-montmorillonite, ehe tagged compound remainin g at the starting line.
Table II show s clay migration resulting from percolation with water only in the textural fractions, down to 0.06 mm diam. This occurs to a m e asurable extent only with coarse sand (2 - 0.2 mm diam.). In the c olumns with particle si zes of less than 0.06 mm diam. the whole tagged c lay remained immobile in the top l ayer where it was administered.
TABLE II. MIGRATION OF TAGGED MONTMORILLONITE IN FIVE SOIL COLUMNS WITH DIFFERENT TEXTURAL FRACTIONS
(mm diam.) lst percola ti on 2nd percola tion 3rd percolation 4th percola tion 5th percolation Total
(cpm/litre) ( cpm/litre) ( cpm/li tre) ( cpm/li tre) (cpm/litre) (cpm)
1 - 2 516 210 387 230 386 - - 903 826
0.2 - 1 204 118 318 050 821 - - 522 989 0.06-0.2 - 217 557 - - 774 0.02 - 0.06 - - - - - - 0.02 - 0.002 - - - - - -
"' CX> "'
~ ~ ~ ~ cn trl
~ II> ::i c..
2. THIN-LAYER CHROMATOGRAPHY
Thin- layer chrom atography of plated soil / or clay / silic a - gel / starch mixtures (13:15:2) is used to test migration and fixation processes of ions, humic matter or clay minerals in the soil .
FIG.3. Set-up of high-pressure autoclaves in a tube-oven.
It can also be applied exclusively to a certain fraction of the soil- plus-starch binder either in conventional discontinuous partition chromat- ography or in continuous flow chromatography. Again, 55Fe-clay, well dispersed by ultrasonic treatment, is administered at a sequence of points on the starting line. Only with the coarse sand fraction was there observed a scanty clay translocation within the lower Rf-region (see Fig.2).
3. HYDROTHERMAL TREATMENT
The general belief that the textural differences, i. e. higher concen- trations of the clay fraction in the B1 -horizon (clay accumulation) of
284 SCHARPENSEEL and KERPEN
lessive-profiles, exist as a result of clay migration , is disputed. Model experiments in colurnns with undisturbed soil profiles indicate leaching and percolation of considerable quantities of colloidal Si02 , alurninium an~ other required solvent associates, that might equally well form the excessive clay, wholly or in part, on the site of the Bc-horizon.
The potentialities of this alternative mechanism can be estimated by the comparative testing of newly formed clay-yields in the various profile horizons owing to mutual hydrothermal treatment in a high-pressure autoclave. As described in Figs. 3 and 4 truncated cylinders with repre- sentative soil samples of the genetic horizons, previously rnixed with finely ground 55Fe(OH)a (20 g soil + 6 rnl ~0+20 rng 55Fe(OH)3 ), were piled up in the autoclave (Fig. 4) and treated hydrotherrnally for 42 d at 225°C and 50-atrn steam pressure.
FIG.4. High-pressure autoclave filled with truncated cylinders containing soil of the different horizons.
The hydrothermally newly formed clay minerals, from the components available in the various horizons, were labelled with 55Fe, i. e. incorpo- rated in the clay minerals by isomorphic exchange for aluminium (see the basic constituents of clay synthesis, Table I).
After hydrothermal treatrnent the soil samples were transferred into sedirnentation cylinders. Only the clay fraction of less than 2 µm diarn. is recovered and extracted with a dithionite-solution (40 ml 0.3 M Na- citrate- solution + 5 rnl 1 M Na2(HC03ksolution+l g Na-dithionite) so as to rernove all the rem