Jül - 514 - LW Januar 1968 KERNFORSCHUNGSANLAGE JOLICH GESELLSCHAFT MIT BESCHRÄNKTER HAFTUNG Institut für Landwirtschaft Studies on tagged clay migration due to water movement by H. W Scharpenseel and W. Kerpen - Als Manuskript gedruckt
-Kerpen - juser.fz-juelich.dejuser.fz-juelich.de/record/830490/files/Jül_0514-LW_Scharpenseel.pdf1.50-m-long glass columns, in the upper zone of undisturbed soil profiles. By perfusion
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 micromorphological 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
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 welldefined 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 background (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
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 soilplus-starch binder either in conventional discontinuous partition chromatography 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 concentrations 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 representative 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. incorporated 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 remaining free unbound 55Fe. Finally the clay fractions were tested for their specific activity by suspension counting in.a liquidscintillation spectrometer. The specific activities rneasured were directly related to the clay-forming ability of the various genetic profile horizons.
Results so far available (Table III) consistently show that newly synthesized clay occurs more frequently in the A1- and B/C-horizons. While, in the A1-horizon, part of the 55Fe might be tied up in stable clay-
humic acid-complexes with Fe-cation-bridge (7], the pronounced clayforming predisposition in the B/C-horizon is genuine, and points to tendencies for clay to form in the transition zone between calcareous loess (Cc-horizon) and the decalcified, weathered loess-material of the Br-horizon. This, however, confirms the supposition that the higher clay content in the Br -horizon might at least partly stem from the development in loco because of the particularly favourable supply conditions with the required percolated structural components.
4, CHEMICAL AND PHYSICAL COMPARISON OF THE CLAY MINERALS IN THE Ab- AND A1-HORIZON WITH THOSE ALONG THE PLASMATIC FLOW STRUCTURES
Studies are under way to compare the general clay fractions of the Aband A1 -horizons with the silicous-clayey substance, scraped off the plasmatic flow structures. Only if it is identical can the material from the plasmatic flow structures be considered to be translocated because of the clay-migration--mechanism. Appropriate methods are:
X- ray diffraction analysis (control of background level due to amorphous matter); Differential-thermo-analysis; Electron-microscopy; Infra- red spectroscopy; and 28Si/29Si/30Si-isotope ratio measurement.
The problem of whether or not in terrestrial soils, such as Parabraunerde, grey brown podsolic, sol brun lessive, dernopodsol and hapludalf, clay particles can be transported downwards with the flow of percolating water, is still open to question. So far the clay-migration concept is based on indirect evidence. Five different methods, mainly involving the use of tagged material, are described:
( 1) Tagged clay was found to remain concentrated in the upper layer when administered to large undisturbed soil-profile columns. Even after several years of repeated percolation this did not change.
(2) 55Fe-labelled clay, administered to the upper layer of columns filled with varying soil fractions, showed a marked clay migration in the coarse- sand range of 2 - 0.2 mm diam., and a slight migration in the range down to 0.06 mm diam.
(3) Thin-layer chromatography with different soil fractions reveals only a very slight clay migration and only in the coarse sandy soil fraction.
(4) Hydrothermal treatment of material from all genetic horizons of Parabraunerde, mixed with 55Fe(OH)3, consistently yields the highest specific activity of the clay fractions in Ab- and BC-horizon. The highest ability to produce clay seems to be associated with the transition zone of decalcification, superimposed on to the calcareous loess, in direct contact with the clay-accumulation zone (Br) above.
This at least points to a certain degree of new clay formation in or adjacent to the clay- accumulation horizon, apart from the clay migration alone claimed up to now.
TABLE III. SPECIFIC CLAY-PRODUCING ABILITY OF DIFFERENT HORIZONS IN PARABRAUNERDE PROFILES BELOW FOREST AND FIELD
Parabraunerde below forest Parabraunerde below field (Roesberg) (Gelsdorf)
(5) Comparative tests of the clay in the Ab- and A1-horizons with the clayey material of the plasmatic flow-structures in the Bt-horizon must show identical characteristics, if the clay-migration concept is tobe maintained. Experiments such as those done by X-ray diffraction tests, DTA, electron-microscopy, infra-red spectroscopy and 28Si/29Si/30Siisotope ratio measurement are being carried out.
[l] SCHARPENSEEL, H. W., GEWEHR, H. , BECKMANN, H., Die Herstellung radioaktiven Montmorillonits und seine Verwendung zu bodenchemischen wie -morphologischen Studien, Z. PflErnähr. Düng. Bodenk. 101 2 (1963) 122.
 BECKMANN, H., GEWEHR, H., SCHARPENSEEL, H. W. , Über eine Synthese radioaktiver Tonminerale, Landw. Forsch. 17. Sonderheft (1963) 161.
 SCHARPENSEEL, H. w., KERPEN, W •• Modellversuche an ungestörten Bodensäulen zum Studium bodengenetischer Bildungsmechanismen unter Benutzung radioaktiver Bodenkonstituenten, z. PflErnähr. Düng. Bodenk. 101 1 (1963) 1.
 KERPEN, W., SCHARPENSEEL, H. W., SCHOEMBS, !. , Untersuchungen der Perkola,te ungestörter Bodensäulen, MitL dL Bodenkund. Gesellschaft i (1965) 151.
 SCHARPENSEEL, H. W ., Zur Darstellung der Wanderungsfähigkeit und Festlegung von Ionen und Kolloiden in dispersen Systemen, MitL dt. Bodenkund. Gesellschaft i (1966) 139.
 SELKE, M., Die Böden Süd-Niedersachsens, Wirtschaftswissenschaftliche Gesellschaft zum Studium Niedersachsens 12 (1935).
 SCHARPENSEEL-;-H. W ., Aufbau und Bindungsform der Ton-Huminsäure-Komplexe, Teil 1 und 2., z. PflErnähr. Düng. Bodenk. 114 3 (1966) 175.
P. A. C. RAATS: Did you attempt in your column experiments to saturate the clays with any particular ion? The mobility of the clay would appear to depend strongly on the type of exchangeable ions present.
H. W. SCHARPENSEEL: Following synthesis the labelled .montmorillonite is mainly calcium -saturated, but after washing with a solution of sodium citrate + sodium bicarbonate + sodium dithionite it is preferentially sodium:-saturated. After it has been fed to the columns and percolated, the superficial cations are quickly equilibrated with the medium, in which ca++ constitute 70-80% of the exchange cations coating the clay minerals.
P. A. C. RAATS: The predominance of plasmatic flow structures on the walls of large pores, cracks and so on strongly suggests that these structures cannot be explained in terms of in-situ clay formation.
H. W. SCHARPENSEEL: The pores with plasmatic flow are not very large - some25-60µmindiameter - andclayformationfromthedownwardmoving soil solution is quite feasible.
M.DE BOODT: Have you allowedfordryingofthe soilinyourcolumn experiments? One would expect the mechanical movement of the clays to occur through the fissures, which in Parabraunerde are sufficiently large (200 µm in diameter) when the water tension rises to 30 atm or more.
H. W. SCHARPENSEEL: For two days each month water is percolated through the soil columns. In the intervening period the soil dries until it reaches a condition somewhere between field capacity and the wilting
288 SCHARPENSEEL and KERPEN
point. In view of the good water-holding capacity of loess, this procedure corresponds fairly well to field conditions.
M. DE BOODT: I should have thought it would be more logical to expect clay to form in the B 1 rather than the Bc/C horizon, the higher 55F'e activity in the latter being caused by the formation of iron phosphate or some other chemical with the ions present.
H. W. SCHARPENSEEL: The tendency for clay to form mainly in the Be/Ce horizon accords well with our experience of hydrothermal clay synthesis, from which we have come to expect maximum formation of montmorillonitic /illitic clay minerals in the region of maximum Si°'2 and ca++ availability. Iron phosphate formation does sound chemically feasible, but it is not substantiated by iron and phosphate values obtained by analysing the soil in different horizons.
W. KERPEN: I should like to amplify Mr. Scharpenseel 1 s reply. Clay formation depends on the ratio of Si02 to bivalent cations. Since the availability of silicic acid is about the same in all horizons, the bivalent cations (particularly calcium) determine the extent of clay formation. The greatest availability of bivalent cations, together with a suitable amount of water, is in the B 1 /C horizon.
D. J. BROWN: Did you determine the mineral distribution throughout the soil columns before carrying out your tests? If so, was there any correlation between mineral content and clay formation?
W. KERPEN: The reasons for the concentration of clay enrichment in the Bt horizon can be extremely varied. For example, they can be genetic, that is to say, associated with clay migration or formation. Alternatively, they can be geological - associated with the stratification of substrata with different clay contents. We were interested in the former processes and accordingly used Parabraunerde (which is similar to the grey brown podsolics) for the column experiments. The initial material, Würmian loess, was mineralogically uniform from the surface down to the subsoil, so that the formation of horizons with reduced and enhanced clay contents could be due only to clay migration and/or synthesis.
Nevertheless, we performed a wide range of soil analyses, including mineralogical, structural, radiographic, electron-optical, micromorphological and other physical studies.
Data on the correlation between mineral content and clay formation, obtained from hydrothermal synthesis studies, have been published in the following papers: Landw. Forsch. _!1 Supplement (1963) 61, and z. PflErnähr. Düng. Bodenk. 101 (1963) 122.
M.J. FRISSEL (Chairman): Many substances, such as DDT, are insoluble in water. Nevertheless these compounds are transported downwards. Some authors assume that they are adsorbed on and transported together with clay particles. Does your model allow for such a phenomenon?
H. W. SCHARPENSEEL: No, we did not attempt to study chelating processes. While podsols would favour such processes the Parabraunerde would probably not, since the organic matter is inherently stable mull and the clay migration rate is too slow to allow direct observation.
O. TEODORU: In the literature opinions differ as to the role of different fractions in the microstructure of soils. In the light of your results, what influence do you think clay has on the formation of microaggregates?
H. W. SCHARPENSEEL: This question relates rather to paper SM-94/8, 1 in which micromorphological and thin-section autoradiographic evaluation is the final aim of the protracted column percolation tests.
Unfortunately, it is impossible to answer the question at present, since the first series of Parabraunerde columns has only just reached (after four years of percolation and chemical measurements) the stage where thin sections are being prepared. The tagged clay that has been added will become visible within its micromorphological environment.
M. DE BOODT: The formation of microaggregates is completely dependent on the kind of cations absorbed on the clay minerals, on the concentration of the ions and on the speed and number of the wettingdrying cycles.
1 KERPEN. W .• SCHARPENSEEL, H. W., "Movement of ions and colloids in undisturbed soil and parent rock material columns", these Proceedings.