PEDOLOGIE Edité avec l'aide financière de la Fondation Universitaire

et du Ministère de l'Education nationale et de la Culture française et du Ministère de l'Education nationale et de la Culture néerlandaise

Uitgegeven met de financiële steun van de Universitaire Stichting en van het Ministerie van Nationale Opvoeding en Nederlandse Cultuur

en van het Ministerie van Nationale Opvoeding en Franse Cultuur

Bulletin de la Société BeIge de Pédologie

Bulletin van de Belgische Bodemkundige Vereniging

1980

XXX, 2

Comité de rédaction Redactiecomité

A. Cottenie, J. D'Hoore, G. Hanotiaux, A. Herbilion, T. Jacobs, A. Noirfalise, G. Scheys, L. Sine,

C. Sys, R. Tavernier, M. Van Ruymbeke

PRESIDENT D'HONNEUR ERE-VOORZITTER

J. Baeyens

SECRETAIRES GENERAL HONORAIRES ERE-SECRETARISSEN -G ENERAAL

R. Tavemier J. Ameryckx

ANClENS PRESIDENTS OUD-VOORZITTERS

V. Van Straelen t F. Jurion t L. De Leenheer G. Manil t A. Van den Hende G. Scheys L. Sine A. Cottenie G. Hanotiaux M. De Boodt A. Herbillon P. Avril J. D'Hoore M. Van Ruymbeke

(1950-1953) (1954-1955 ) (1956-1957) (1958-1959 ) (1960-1961) (1962-1963 ) (1964-1965) (1966-1967) (1968-1969) ( 1 970-1971 ) (1972-1973 ) (1974-1975) (1976-1977) (1978-1979)

PEDOLOGIE, XXX, 2, p. 163-175,1 fig., 4 tab., Ghent, 1980

DISTRIBUTION PATTERNS OF ESSENTIAL AND . NON ESSENTIAL TRACE ELEMENTS IN THE SOIL­SOIL SOLUTION SYSTEM

M.VERLOO L. KIEKENS

A. COTTENIE

Studiecentrum voor Toegepaste Ecochemie I.W.a.N.L.

In recent years one has witnessed an immense increase in public interest and concern over the quality of the environment. Pesticides, radio-activity and smog have been weU known as pollutants, for a num ber of years.

More recently, however, an other class of environmental contamin­ants, the so called "heavy metals" have moved into prominence so that lead, copper, mercury, cadmium and arsenic are now household words ·from which the public only kJ?ows that they are "bad".

According to Andersson (1977) the heavy metals are limited to the group of elements having densities exceeding 6 g/cm3, in practice much more elements may have hazardous effects on the environment.

However, a series of these elements is indispensable to living organ­isms so that one may distinguish between essential and non essential trace elements, although the boundary between these groups is not really sharp and the list of biological important elements is extended year af ter year.

A series of elements, including non essential trace elements, are found in all organisms as they have evolved in the presence of some background concentrations. The biological importance of an element has to be elucidated by biochemical observations and experimentation; in contrast the effect of man made organic pollutants on the food chain can easily be compared with a zero background level.

As weil the essential as the non essential elements have potential hazardous environmental effects which will manifest as soon as a

M. Verloo, L. Kiekens, A. Cottenie - Laboratorium voor Analytische en Agroche­mie, R.U.G., Coupure Links 533 - B-9000 Gent - Belgium.

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critical soillevel is exceeded. For the essential trace elements there exist also minimal soil contents below which deficiency symptoms in plants may occur.

The evaluation of unfavourable situations requires knowledge of the normal contents of these elements and the different equilibrium systems and distribution patterns in which they are involved. It is also meaningful to know the extent and the conditions of release or re­tention of these elements by the soil material thus being stimulated or prevented from uptake by plants and entry into food chains.

1. TOTAL CONTENTS OF TRACE ELEMENTS IN SOILS

Table 1 is giving the average total content of some biological import­ant and other trace elements in soils. Fe and Al being structural elements in most soils have an average total content exceeding some orders of magnitude that of other elements; however from the view­point of biological importance they belong to the group of trace elements. Only the elements Fe, Mn, Zn, B, Cu and Mo are really essential to plants while Al, Co, Ni, Pb, Cr, F , I, Se and probably also V and Sn can biologïcally be important.

Table 1

Average total content of biological important and other trace elements in soUs in mg/kg soil (Cottenie et al., 1979)

Biological important trace elements Other trace elements

Mn 500 V 100 Ba 500 La 25 Zn 50 Ni 50 Zr 500 As 10 Cu 20 Cr 50 Sr 500 Be . 5 B 15 F 25 Rb 100 Ag 1 Co 5 Pb 10 Li 75 Cd 0.5 Mo 2 Sn 5 Ge 50 Hg 0.1

I 1 Y 25 Se 0.2

Al 5 0.000 ppm in soils 1 acting as ttace elements in plants Fe 25.000 " " " Ti 5.000 " " "

The average total content of trace elements in Belgian soils is summarized in table 2 from which also can be noted that mainly the Fe and Al contents are related to soil texture.

164

L

Table 2

Average total content of some trace elements in Belgian soUs (contents in mg/kg soU)

SoU texture ppm

Fe Al Mn Zn Cu Pb

light 5537 6327 112 41 12 26 medium 14166 13316 271 77 15 26 heavy 13778 14180 160 37 12 21

Total trace element contents are especially of geochemical interest and can seldom be used as an appropriate criterion for plant availabil­ity, the element fraction incorporated in unweathered minerals has no direct biological significance. Nevertheless, the total content may be used in pollution control to fix a limiting level not to be exceeded without a real danger for noxious effects. In 1975 the FAO Soils Bulletin (Tiet jen, 1975) published a proposal giving for some elements the tolerable total contents in soils (see table 3).

Table 3

Tolerabie total contents of trace elements in soils (proposal)

Element ppm

F 500 Zn 300 Cu 100 Cr 100 Be 100 Ni 100 Pb 100 Co 50 As 50 Se 10 Mo 10 Cd 5 Hg 5

For the analytical determination of the total trace element content of soils many methods have been used but only few techniques really give total contents, namely : - neutron activation

165

- emission spectrography or spectrometry on the soil-powder - X-ray fluorescence on a soil-pearl - spark-source mass spectrometry - determination af ter alkaline fuse - determination af ter attack with boiling concentrated strong acids.

Other techniques based on extraction, only release a fraction of the total element content, this, has to be taken into account when inter­preting soil analytical data.

2. FRACTIONATION AND MOBILITY OF TRACE ELEMENTS

The total amount of trace elements in soil may be split up in some more or less distinct fractions related to their solubility or the chemic­al compounds they are incorporated. An available fraction of trace elements is difficult to define because of its variability and dependence on interactions with different soil constituents which are governed by phenomena like : -.:. precipitation and solubilization - adsorption and desorption - complexation and decomplexation.

The nature of interaction and its importance depends on several soil parameters, such as : - the concentration of the ions in the soil solution - the type and abundance of adsorption sites associated with the

solid phase - the concentration of ligands capable to form organomineral com­

plexes - the pH and redox potential of the soil.

To release a biologically active, or plant available fraction different extracting solutions have been used. The reliability of an extraction method is often determined by the existence of a more or less significant correlation between the amount extracted and the plant uptake or content.

It is well known that plants are able to take up nutrient elements from different soil fractions or pools: - the soluble fraction; direct uptake of free ions - the exchangeable fraction; uptake af ter exchange or by direct

contact exchange - the complexed fraction; uptake of chelated elements or organo­

mineral complexes. An efficient extracting agent should withdraw the same fractions

to a comparable extent.

166

It is evident that in this concept the plant itself can be used as an extracting agent and plant uptake, in this case, is a direct indicator for the availability of elements in the soil.

For practical reasons however, the use of plants for the determina­tion of the trace element status of a soil can seldom be ll:sed, partially because plant growing may be a time consuming business but also be­cause of interpretation difficulties as different plant species will take up different amounts of trace elements from the same soil.

Plant uptake or biological significance of an element mainly de­pends upon its MOBILITY.

The mobile fraction of an element is defined as the sum of the soluble amount in the liquid phase and an amount, retained by the solid phase, which can be transferred to the liquid phase of the soil. The transfer may occur as a consequence of chemical, physico-chemic­al and biological conditions such as variations of pH, redox potential, root activity, etc. Thus the parameters that control the mobility of an element will also control in a great extent the potential biological activity. These parameters are : pH, nature and abundance of the mineral sorption complex (clays), nature and abundance of soil organ­ic matter and redox potential, which are subjected to a detailed discussion.

2.1. Influence of pH on the mobility of trace elements

pH is probably the most important parameter controlling the mobility of trace elements in the soil system. Besides its direct effect pH has also an indirect effect since it affects many reactions in which the mineral sorption complex, organo mineral complexes or redox­potential are involved.

The direct effect of pH on thé mobility is mainly reflected in the precipitation and dissolution of trace elements in function of pH, being the transfer from the solid to the liquid phase or reverse.

Theoretically it is possible to predict the solubility of the elements in most chemical compounds that may be found in soils. From the solubility product KS = (M)a(A)b of a compound MaAb, in which Ma denotes "a" atoms of any cation Mand Ab "b" atoms of any anion A, the solubility of the free ion M can be calculated.

Dhaese (1977) thus determined the influence of pH on the solubility ofPb++ Cd++ Ni++ Cr++ Cr+++ Mn++ Cu++ Zn++ Co++ and Co +++. He sho~ed that the 'low sol~bility ~f.som; me tal' phosphates may be a determining factor limiting the mobility of some metal ions in the soil solution.

167

The work ofLINDSAY (1972) gives some fundamental considera­tions concerning the influence of pH on the micronutrient equilibria. He determined experimentally the relationship between the solubility of some metal ions in soils and pH. An example of these relationships is given by the following equations

(Zn++) = 106 (H+)2 or p Zn++ = 2 pH - 6 (Cu++) = 103.2 ~H+d2 or p Cu++ = 2 pH - 3.2 (Mo04 2-) = 10- O. / (H+)2 or p Mo042- = 20.5 - 2 pH

These equations show that the activity of the cations Zn++ and Cu++ in the soil system is proportional to the square of the proton activity while the Mo042- activity is inversely proportional. All trace elements that behave in the soil as cations show an increased solubility with decreasing pH while those occuring as anions, Mo042-, B033- and Se042- are more soluble at higher pH.

The transfer of an element from the solid to the liquid phase of the soil can be studied by the determination of its mobility in function of pH. Experimentally this is carried out by equilibrating a soil suspension at decreasing pH values by addition of HN03' The concentration of elements in the solution at any pH thus corresponds to a mobile fraction at that fixed pH.

Table 4 gives some examples of trace element mobility in three different structured soils in function of pH.

As can be seen, a decrease of the pH of the soil sus pension results in an increase of the concentration of trace elements in the soil solu­tion, which may be explained by a simultaneous action of the follow­ing mechanisms : - desorption phenomena as a consequence of increased H+ concentra­

tions - solubilization phenomena at low pH values - decomposition of organo-mineral complexes.

From fig. 1, giving the mobilization pattern of some trace elements in a light textured soil as a fraction of the total content, it can be seen that different elements behave in different ways when pH of the soil suspension is decreased. It is clear that the slightest pH-change of the equilibrium solution may result in considerable differences of the mobilized amounts.

It can be concluded that when interpreting analytical data of trace element determinations in soils, pH of the extracting solution and the extract, the equilibrium solution, has to be known,as the direct effect of pH on the mobility of these elements is generally strongly pro­nounced.

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Table 4

Influence of pH on the release of Zn, Mn, Cu and Fe from 3 soils of different texture (results in mg/kg soil)

Soil texture pH of mg/kg soil released . sus-

Zn Mn Cu Fe pension

light 5.6 0.20 0.25 0.50 0.5 (Waarschoot) 4.0 2.20 11.00 0.55 2.3

3.0 4.30 18.25 0.55 3.6 2.0 8.30 38.25 1.80 7.2 1.0 10.10 60.00 8.50 84.0 0.5 10.75 68.75 8.70 530.0

medium 5.7 0.05 2.25 0.10 1.8 (W annegem-Lede) 5.0 0.05 5.60 0.10 4.1

4.0 1.30 16.50 0.35 6.6 3.0 3.85 40.75 1.00 8.8 2.0 7.70 100.00 4.50 11.0 1.0 11.15 142.50 11.25 121.3 0.5 12.50 144.00 13.60 575.0

heavy 7.1 < < < < (Pervijze) 6.0 0.10 < < <

5.0 0.15 1.65 < < 4.0 0.50 11.35 < 0.8 3.0 0.80 34.25 < 1.5 2.0 4.50 90.00 0.35 9.3 1.0 12.00 128.75 3.50 240.6 0.5 13.30 131.25 4.35 575.0

< contents below the limit of detection.

2.2. Influence of the nature and abundance of the mineral sorption complex on the mobility of trace elements

The mineral adsorption complex of a soU consists of very finely particulated soU solids (day partides, amorphous oxides of Fe and Al), having a high specific surface area and generally showing a net negative surface charge. A portion of the chemical elements in soU is in the form of cations that are not components of inorganic salts. Their con­centration in soU solution is mainly buffered by a system of ion-ex­change reactions, whereby adsorption of a certain amount of cations is accompanied with the release of equivalent amounts of other cations. When upon adsorption of cations less than equivalent amounts of other cations are released, the process is called superequivalent or specific adsorption.

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%of tot a , mobilized

100

90

80

70 Pb

60

50

4

30

20

10

7.5 7 6 5 4 3 2 0.5 pH

Fig. 1.

Mobilization pattern of Pb, Cd, Cu and Zn in a light textured soil.

It is clear that the desorption of trace elements increases their mobility. The adsorption-desorption behaviour of trace elements in soils is influenced by several parameters: - due to the relative low content of trace elements in soils in com­

parison with the major elements, an important competition from the latter for adsorption sites may be expected. Kiekens (1980) studied the adsorption of Zn, Cu, Cd and Pb by soils suspended in H20 and 0.01 n CaCI2. Adsorption was strongly reduced in the presence of Ca 2+ ions, indicating that they compete effectively with trace elements for the adsorption sites. At soil pH, the exchangeable quantitiés of trace elements are gener­ally much higher than their water soluble fraction. Desorption of trace elements becomes very important below a certain pH, which is characteristic for each element. This critical pH value is about 5 for the cations Zn2+, Cd2+, Mn2+ and 3 for Cu2+ and Pb 2+.

- A more or less important fraction of trace elements may be involved in specific adsorption reactions. This is manifested in a selective up­take of trace elements by soil colloids .. The order of selective up­take and the extent of specific. adsorption are influenced by several

170

parameters such as : properties of the ion, formation of hydroxy­complexes, number of pH dependant adsorption sites, steric factors, specific reactions with amorphous oxides.

- The involvement of trace elements in specific adsorption reactions may result in the occurrence of a quantitatively important adsorp­tion-desorption hysteresis effect, which seems to be of greater im­portance at low occupancy of the adsorption complex with trace elements. Adsorption-desorption hysteresis reduces the mobility of trace elements in soils and is also largely affected by soil properties such as day and organic matter content, texture and CEC.

Extracting solutions that have been used for the determination of exchangeable trace elements in soils generally contain considerable amounts of displacing cations such as NH4+, Na+ or Ca++. The natur~ of the accompanying anion may increase the extracting capacity as, acetates, chlorides, lactates or fluorides are able to form soluble com­plexes with some cations.

Also in exchange reactions pH interferes as a controlling agent, the H+ activity does not only act on the dissolving power of the solution but also seems an effective displacing agent. Therefore the use of buffered solutions for the determination of the exchangeable trace element fraction is a must while also the nature and concentration of the displacing cation and accompanying anions should be considered to obtain comparabie analytical results.

2.3. Influence of the nature and abundance of soil organic matter on the mobility of trace elements

Organic matter is an important soil component originating from decaying plant material which by chemical and biochemical trans-:­formations is converted to a more or less stabie product known as humus.

Chemically humus belongs to the group of polymers or poly-electro­lytes, it has functional groups that dissociate in water and carry a pH-dependent electric charge.

According to their solubility humic substances can be separated in­to humic acids and fulvic acids.

Humic acids are soluble in alkali but insoluble in acid, while fulvic acids are soluble in both alkali and acid. Their chemical configuration is similar but humic acids have higher molecular weights than fulvic acids. Humic acids and fulvic acids show different interaction patterns with trace elements. Fulvic acids mainly form chelates with metal ions

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thus increasing their mobility and solubility over a wide pH range (0.5 - 11).

Most soluble heavy metals that occur in surface waters or in the soil solution are bound to a yellow compound with fulvic acid properties. In a soilleachate 93 % of the soluble Cu was bound in this way, for Pb, Fe, Zn and Mn these percentages were respectively 59, 23, 16 and 1 % (Verloo, 1979).

This also indicates that there is a selectivity of fulvic acids towards the metal ions. According to Stevenson & Ardakani (1972) the stability constant (log K) of metal fulvic complexes decreases in the following order

log K at pH 3.5 Cu >Fe >Ni > Pb >Co >Ca >Zn >Mn>Mg 5.8 5.1 3.5 3.1 2.2 2.0 1.7 1.5 1.2 log K at pH 5.0 Cu >Pb >Fe >Ni > Mn>Co>Ca >Zn >Mg 8.7 6.1 5.8 4.1 3.8 3.7 2.9 2.3 2.1

It is worth mentioning that the complex stability increases from pH 3.5 to pH 5. Verloo (1974) showed that in fact two stability maxima occur, one at about pH 6 and another at pH 9.

Humic acids mainly form insoluble complexes with metal ions thus decreasing their mobility. Here pH has not only an effect on the stability of the complexes but also on the solubility. Indeed in acid medium the humates are insoluble but as the pH increases to 4 or more they start to dissolve gradually forming a colloïdal system that generally is flocculated by the action of Ca++, Mg++ and eventually Fe+++ and AI+++ in the soil solution. Only in extreme conditions of leaching or if Na + becomes the dominating ion in the soil solution the colloidal complexes are peptized and are mobilized in the soil system.

Thus soil organic matter may he considered as an important regulator of the mobility of trace elements in soils. - the fulvic acid fraction will mainly form soluble complexes with

metal ions, thus increasing their mobility. However, these complexes are less stahle than the corresponding humic acid complexes.

- humic acids mainly form insoluble complexes so they can be con­sidered as the organic storage place for heavy metals.

When an extracting method is used to determine the trace element status of soils it is clear that any solution will extract the soluble com­plexes. The element fraction bound as insoluble organo-mineral com­pi exes is only extractable af ter d~ssolution, or destruction of the com-

172

plex or release of the element fr om the complex by stronger complex­ing agents.

The complexes are partially soluble in NaOH or may be decomposed by heat in the presence of strong oxidizing agents such as H202' Re­lease of metal ions from the complex is possible by the action of strong chelating agents such as EDT A or DTP A.

2.4. Influence of the redox potential on the mobility of trace elements

Redox potential as a parameter for the oxidation-reduction state of a soil may be a determinant factor in the specification of the chemic­

al form of a nutrient or toxi~ metal. Basical work on the effect of redox potential on soils and sediments has been done by Ponnampe:­ruma (1972) and Khalid et al. (1977).

The influence of redox potential on trace element behaviour can be summarized as follows : - reduction of a soil will, in a first phase, result in an increased

mobility of many trace elements. There is a direct effect on the soluhilites of Fe and Mn compounds whose reduced ions Fe++ and Mn++ are more soluble than the oxidized ones. Indirectly the dissolution of ferric and manganic oxides also releases other occluded trace metals.

- in severe reducing conditions the mohility of most trace elements will decrease as insoluble sul fides may be formed. The strong re­ducing conditions correspond with redox potentials below - 150 m V and generally are found in flooded soils or sediments hut also in soils suffocated by impermeable pavements or subjected to gas leaks very high sulfide concentrations can built up.

- oxidizing conditions generally stimulate the mineralization rate of organic compounds, thus elements fixed or complexed hy organic matter are released and transferred to other fractions in the soil system, this also may alter the mobilization pattern of trace metals.

3. CONCLUSIONS

As described trace element behaviour and biological activity in soils is directly related to mobility and controlled hy a series of parameters like pH, sorption capacity and saturation and redox potential.

During the analytical determination of trace elements these para­meters are altered to release a certain fraction of these elements. Differ­ent extracting agents may mobilize quite different fractions and amounts. Based on these considerations the interpretation of results on chemical analysis of heavy metals in soils is impossible without de-

173

tailed analytica! specifications about the methods used. The choice of methods has to depend on the objectives of the study, meaning that procedures used for pollution purposes may differ from those for soil fertility.

LITERATURE

1. Andersson A., (1977). Heavy metals in Swedish soils : on their retention, distribution and amounts Swedish J. argric. Res. 7, 7-20.

2. Cottenie A., Camerlynck R., Verloo M., Dhaese A., (1979). Fractionation and determination of trace elements in plants, soils and sedi­ments Pure & Appl. Chem., 52, 45-53.

3. Cottenie A., Kiekens L., (1972). Exchange of Zn, Mn, Cu and Fe in relation to saturation of the soil complex. Potassium in soil, 9th IPI-Colloquium, Landshut, W-Germany 91-101.

4. Dhaese A., (1977). Invloed van anorganische verontreinigingen op de relatie bodem-water-plant. Doctoraatsthesis, Rijksuniv. Gent.

5. Khalid R. A., Gambrell R. P., Verloo M., Patrick W. H. Jr., (1977). Transformations of heavy metals and plant nutrients in dredged sediments as affected by oxidation reduction potential and pH. Final report. Waterways Experiment Station. Corps of Engineers, P. O. Box 631, Vicksburg, Mississippi.

6. Kiekens L., (1980). Adsorptieverschijnselen van zware metalen in gronden. Doctoraatsthesis, Rijkuniv. Gent.

7. Kiekens L., (1975). Studies on the adsorption and desorption of Zn by soils. Med. Fac. Landbouww. Rijkuniv. Gent, 40, 1481-1492.

8. Lindsay W. L., (1972).

Inorganic phase equilibria of micronutrients in soils. In : Micronutrients in Agriculture. Soil Sci. Soc. Amer. Inc., Madison, Wisconsin.

9. Ponnamperuma F. N., (1972). The chemistry of submerged soils. Adv. in Agron., 24, 29-96.

10. Stevenson F. J., Ardakani M. S., (1972). Organic matter reactions involving micronutrients in soils. In : Micronutrients in Agriculture. Soil Sci. Soc. Amer. Inc. Madison, Wisconsin.

11. TietjenC., (1975). Principal problems of the use of city wastes for crop production and soil con-

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servation. In : F. A. O. Soils Bulletin 27, 221-226.

12. Verloo M., (1974). Komplexvorming van sporenelementen met organische bodemkomponenten. Doctoraatsthesis, Rijksuniv. Gent.

13. Verloo M., (1979). Influence of soil organic matter on the behaviour of heavy metals in soils and sediments. In : Essential and non essential trace elements in the system soil­water-plant. Laboratorium voor Analytische en Agrochemie, Rijksuniv. Gent.

Summary

The distribution patterns of trace elements in soils are discussed. Total element content is mainly of geochemical interest while the determination of a biological active fraction is related to the mobility of trace elements. The parameters that control this mobility, pH, nature and abundance of the mineral sorption complex, nature and abundance of soil organic matter and redox-potential are commented and practical proposals in relation to analysis of trace elements in soils are made.

Distribution des éIéments traces essentiels et non essentiels dans Ie système sol­solution du sol

Résumé

La distribution des éléments traces dans les sols est discutée. Leur teneur totale est principalement d'intérêtJgéochimique tandis que la détermination d'une frac­tion biologiquement active dépend de la mobilité des éléments traces.

Les paramètres qui controleflt cette mobilité, pH, nature et abondance du complexe de sorption minéral, nature et abondance de la matière organique et Ie potentiel d'oxydo-réduction sont étudiés et des propositions pratiques concernant l'analyse des éléments traces dans Ie sol sont faites.

Verdeling van essentiële en niet essentiële sporenelementen in het systeem bodem­bodemoplossing

Samenvatting

De verdeling van sporenelementen in gronden wordt besproken. Het totaal ge­halte is hoofdzakelijk van geochemisch belang terwijl de bepaling van een biolo­gisch aktieve fraktie verband houdt met de mobiliteit van sporenelementen.

De parameters die een invloed uitoefenen op deze -mobiliteit, pH, aard en hoe­veelheid van het mineraal sorptiekomplex, aard en hoeveelheid organisch mate­riaal en de redoxpotentiaal zijn bestudeerd en praktische voorstellen in verband met de analyse van sporenelementen zijn geformuleerd.

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J

,

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PEDOLOGIE, XXX, 2, p. 177-190, 5 fig., Gand, 1980.

MODELISATION DE LA MIGRATIOND'ELEMENTS DANS LES SOLS

IV. LES MODÈLES DISCONTINUS

GÉNÉRALITÉS

L. SINE J.-P. AGNEESSENS

Dans les articles précédents (L. Sine & J. P. Agneessens, 1978, L. Sine, J. P. Agneessens & Ph. Dreze 1978) nous avons envisagé les sché­mas de modélisation à partir d'un système continu et nous avons décrit les mouvements en introduisant Ie concept de dispersion longitudinale.

On peut aboutir à des résultats numériques analogues en recourant à un autre schéma de modélisation faisant appel à une succession de cellules en cascade. Au niveau de la représentation des concentrations, Ie modèle est discontinu. Ce type de modèle est discuté par J. viller­maux (1972).

Nous établissons ei-après les analogies entre modèles continus et discontinus en considérant tout d'abord les modèles les plus simples que nous caractérisons de la façon suivante : - Ie mouvement du fluide est déterminé par la dispersion longitudi­

nale et sa vitesse moyenne. n n'y a pas de zones stagnantes; - la répartition du soluté est déterminée par sa distribution entre la

phase fluide et la phase adsorbée; - les réactions entre phase liquide et phase adsorbée sont linéaires,

réversibles et instantanées; - Ie flux est conservatif: il n'y a pas de réactions chimiques d'appari­

tion ou de disparition de matlètes (autres que les réactions d'adsorp­tion-désorption).

Nous envisagerons ensuite les modèles plus complexes dans lesquels la ph ase fluide se répartit entre zones mobiles et zones stagnantes ou entre zones circulant à vitesses différentes, la répartition du soluté

L. Sine - Chaire d'Hydraulique agricole. Faculté des Sciences agronomiques de l'Etat à Gembloux, Belgique. J .-P. Agneessens - Comité de recherche SUf l'utilisation des pesticides en agricul::. ture (I.R.S.I.A.). Chaire d'Hydraulique agricole Gembloux, Belgique.

177

étant caractérisée par sa distrihution entre les diverses phases fluides et les diverses phases adsorhées correspondant à chaque zone du fluide.

Les modèles simples discontinus sont appelés modèles en cascades (M. C.) et sont à com parer aux modèles continus à dispersion axiale appelés P. D. (Piston-Dispersion).

Les modèles complexes discontinus sont appelés modèles MCE (Mélange en cascade avec échange de matière) et sont à mettre en com­paraison avec les modèles continus à réactions non instantanées appe­lés modèles P. D. E. (Piston-Dispersion et échange de matière).

Cette terminologie est utilisée par Villermaux (1972) et par Moli­nari & Rochon (1976).

Les modèles discontinus simples (modèles M. C.)

On considère que Ie mouvement est assimilahle au passage à travers une succession de n cellules. Chaque cellule a une longueur constante ~ x, une section unitaire (normalement à l'écoulement) un volume utile (3 !:::. x, et est parcourue, dans Ie sens des x, par un flux U.

Dans chaque cellule Ie mélange est parfait et instantané. L'évolution de la concentration en soluté dans la jème cellule est

décrite par l'équation de conservation de la matière. On a, entre l'in­stant t et l'instant t - dt

[Q !:::. x + U (Cj_1 - Cj)] d t = !:::. x d ((J Cj + P Sj) ( 1 )

expression dans laquelle : t : coordonnée de temps x : direction de l'écoulement j : indice de la cellule envisagée !:::.x : longueur constante de chaque cellule U : flux hydrique traversant la j. eme cellule, à l'instant t, rapporté

à l'unité de surface totale, normalement à la direction x (J : teneur en humidité volumique du sol C : concentration moyenne en soluté de l'eau du sol, rapportée à

l'unité de masse de l'eau S : concentration de la phase adsorhée, rapportée à l'unité de

masse de la phase solide P : masse spécifique apparente de la phase solide Q : disparition du soluté ou de la phase adsorhée par unité de vo­

lume et par unité de temps

Nous postulons en outre que la liaison d'équilihre du soluté entre phase liquide et phase adsorhée est instantanée et linéaire c 'est-à-dire

178

que nous admettons : Sj = k Cj (2)

Enfin nous admettons, pour l'étude des modèles simples . Q = 0 (3)

Réponse impulsionnelle d'un modèle M. C.

Etudions l'évolution de la concentration dans la jème cellule dans l'hypothèse d'une injection impulsionnelle au niveau de la cellule de tête.

Dans cette hypothèse les concentrations initiales et aux limites s'écrivent :

[

t = 0 ,Cj = 0

mO Co (t) = U ~ (t)

j quelconque (~ 1)

(4 )

ö (t) étant la fonction de DIRAC et mo la quantité pénétrant dans la première cellule à l'instant initial, rapportée à l'unité de surface d'é­coulement. (fig. 1)

2 J U

Cl U ~(U'0 U f{

Co Cl C2 J Cj-1 Cj e e e

Fig. 1.

En conséquence et en raison du caractère linéaire des phénomènes invisagés, la réponse impulsionnelle à la sortie de la i me cellule résulte de la convolution du signal d'entrée à travers j systèmes identiques.

L'étude des fonetions de transfert des systèmes linéaires et Ie passa­ge par les transformées de Laplace permettent d'établir que la trans­formée de Laplace de la fonction de transfert résultante est égale à la puissance i de la transformée de la fonetion de transfert d'un réservoir unique.

En recourant aux grandeurs sans dimensions

! t = Ut * (8+pk)b.x

C =C(8+pk)b.x * mO

(5)

179

la combinaison des équations (1) , (2), (3) et (4) devient

. . _ d C*i C*J-1 - C*J - dt (6)

avec pour conditions initiales et aux limites:

{

t* = 0 ; Cj = 0

C*o (t*) = ö (t*) (7)

En passant par les transformées de Laplace, l'équation de la fonction de transfert de la première cellule s'obtient par;

- 1 C*1 = 1 + s

La fonetion de transfert earaetérisant Ie groupe de j eellules en série aura done pour transformée de Laplaee ;

C*j = (1 ~ s ~ et la fonction de transfert sera:

C . = __ 1 - t j-1 exp - t (8) *J U-I)! * *

En repassant aux grandeurs dimensionnelles on obtient :

C. = mO _ 1_ ( Ut ~-1 exp _ Ut (8a) J (8 + p k ) ~ x U-I) ! (8 + P k) ~ x (8 + p k) ~ x

Ie flux étant donné par

[.=UC.= mO ( U )jJ-1 exp - Ut (8b) J JU-I) (8 + pk) ~x (8 + pk) ~x

Moments de l'expression 8

Les propriétés des transformées de Laplace permettent d'établir immédiatement les propriétés suivantes :

I; C*j dt* = 1

IO"'! t * C*j dt* = j

I; t* 2

C*j dt* = j U + 1) (9)

I; t*n C*j dt* = j U + 1) ... U + n-1)

En repassan t aux grandeurs dimensionnelles

180

.j

(9a)

Comparaison entre modèles continus et modèles discontinus

Une première remarque est évidente. Dans Ie modèle discontinu les flux et les concentrations sont liés par l'expression :

f. = U C' J J alors que dans Ie modèle continu, on écrivait :

f=UC-8Do C oX

D étant Ie coefficient de dispersion longitudinale. En second lieu, rappelons que, dans un modèle continu à dispersion

longitudinale et pour des conditions initiales et aux lirnites correspon­dant à (4), on a pour solution

mox f = exp-

tJ4rr Dt _ 8_ 8 +pk

(x_~)2 8 +pk

4Dt _8-8 +pk

(10)

Pour comparer f et ~ c'est-à-dire (10) et (8b) nous commençons par comparer les moments d'ordre 0, un et deux c'est-à-dire les expressions

J; f dt = mO

1.00 t f dt = mO (8 + pk ) x o U

1.00 t 2 f dt = m 0 x 2 (8 + p k) 2 (1 + 2 D8 ) o U2 xU

J; fj dt = mO 00 f d moj (8 +pk) ~x I. t· t = ----==---------o J U

1.000

t fj dt = mO ((8 + pk) ~x)2 j (j + 1) U2

On constate que ces expressions sont identiques si on postule : j ~x = x

j= Ux =~ (11) 2 D 8 2

181

P étant Ie nombre de Peclet :

P= Ux (12) DO

Les valeurs centrales, ou temps de séjour, sont égales à t=(O+pk)x=(O+pk)j~x (13)

U U

Sous cette forme on constate que Ie nombre j de cellules à faire intervenir est proportionnel au nom bre de Peclet et est Hé à la disper­sion longitudinale.

Pour mettre en évidence les différences entre les deux expressions (10) et (8b) no us passerons par les moments du 3ème ordre.

On vérifie que

1.2

1.0

' ~

,8

,6

.2 -

o

Fig. 2.

\ \

\ \,

" ~ ,

4

Evolution du flux en fonetion du temps pour des modèles continus et discontinus Nombre de' Peclet : 2 N ombre de compartiments : 1

x*F* = x (0 +pk) jC* = x (0 +pk) C UmO mO

182

\

3

Fig. 3.

Evolution du flux en fonetion du temps pour des modèles continus et discontinus. Nombre de Peclet: 10 Nombre de compartiments : 5.

1.00 t3 f dt = mO (8 + pK)3 x3

(1 + ~ + 12) o U3 P p2

00 3 f d mO (8 + pK)3 (j ~x)3 (1 +~ +JL) fO t J t = U3 P p2

les différences étant d'autant moins marquées que Ie nombre de Peclet est élevé.

Nous pouvons aussi comparer les expressions (8b) et (10) en les cal­culant pour quelques valeurs typiques de P et en représentant graphi­quement les résultats.

Ainsi que nous l'avons fait précédemment nous exprimerons cette comparaison en reportant

jf ~x (8 + pk) ou fx (8 + pk) mO U mOU

183

',5

.5 -

O+-------~--------~------~r_--~--_r--------~-------o Pig.4.

Evolution du flux en fonetion du ternps pour des rnodèles continus et discontinus Nombre de Peclet : 40 N ornbre de compartiments : 20.

en fonction de :

T = ~ = t* = __ U----'-t ___ _ * t j j(O+pk)tJ.x

Ut x (0 +pk)

Les figures 2, 3 et 4 représentent l'évolution, pour des nombres de Peclet valant respectivement 2, lOet 40 (j = 1, 5 et 20) des valeurs de jC* tirées de l'équation 8 en fonction de T * (T * = tij) et des valeurs de x*F * (L. Sine & J. P. Agneessens 1978) en fonction de T * (T * = t/x*).

Notons que Ie cas de la figure 2 (j = 1), correspond à un seul com-

184

L

partirnent dans Ie modèle discontinu. L'équation 8 se réduit à la forme C* = expo - t*.

Avec l'augmentation du nombre de Pedet, les deux courbes se rapprochent. Pour 5 compartirnents (j = 5, P = 10) elles sont déjà très proches. Pour 20 compartirnents (j = 20, P = 40) les courbes se confondent sur Ie plan des réalités physiques.

Mélange en cascade avec échange de matière non adsorbable (M. C. E.)

Considérons, à l'instar de Molinari & Rochon (1976) Ie mélange is su d'un milieu constitué de j cellules identiques en réponse à une in­jection irnpulsionnelle à l'entrée de la première cellule.

ICj~l I .. : ... :::J-~-j -u Cl

u Cl

Co

Fig. S.

Dans chaque cellule il y a échange entre la ph ase adsorbée et la phase soluble en fonction de la loi

dS, p ~ = k1 (kCj - Sj) (17)

qui remplace la loi (2) d'équilibre instantané Les conditions initiales et aux lirnites sont les conditions décrites

par (4). L'équation (1) est utilisable en tenant compte du (3). On recourt aux grandeurs adirnensionnelles

t = Ut * () f:.x

C = C () f:.x * mO

S = f:.x p S * m o

k1* = ~tx -kl

k = lLK * () La combinaison de (1), (3), (17) et (18) donne:

(18)

185

Le passage par les transformées de Laplace fournit pour chaque cellule, compte tenu des conditions initiales :

{ C:j-.l_- C*j = S ~~j +_S~j) s S*J - kl* (k* C*J - S*J)

On déduit donc la fonction de transfert d'une cellule quelconque de la relation

- - skl*k* C· I=C ·(1+s+ ) *J- *J s + k1*

La fonction de transfert du groupe de j cellules en cascade sera .donc la transformée inverse de la relation :

- s k1 k ~j c· = (1 + s + * *)

J s + k1* ou encore :

k2 k -j C·=(s+k k +1- 1* *)

J 1* * s+k1*

On obtient finalement en utilisant la méthode de transformation inverse utilisée par Lapidus & Amundson (1952)

t)-1 C* (t) = U-1)! exp - (1 + k1* k*) t*

k k 2 k t 11 [ 2J~kI"'--*-k-*-À-( t-* --À-)] L + [ex p (- 1 * t* ) ] 1 * * JO * / 2 U-I) !

V k1*k* À(t*-À)

(22)

11 étant une fonction de Bessel modificée d'or.dre 1.

186

Moments de l'expression 22

En utilisant les propriétés des transformées de Laplace on détermine les moments d'ordre n de la grandeur Cj via l'expression :

dn ej J; te· C*j dt* = ~o (-1~ .,' d sn

On obtient

J; C*jdt* = 1

J; t* C*j dt* = j (1 +k*)

k J; t*2 C*jdt*= (j2+j)(1+k*)2+2j~ (23) 1*

k f; t~ C*j dt* = j(j+1) (j+2) (1+k*)3 + 6j(j+1) (1+k*) k~*

k +3j -*-

2 k1*

En repassant aux grandeurs dimensionnelles

1.00 C' dt = mO o J U

1.00 c. t dt = mO (j ~x) (0 + pk) o J U U (24)

1.00 C. t 2 dt = mO (j ~x)2 (0 +pk)2 [(1+1)+l. p2U _k_] o J U U2 j j (0+pk)2 k1 Ax

1.00 C' t3 dt = mO (j ~x)3 (0 +pk)3 [(1 +~) (1 +~) + ~ (1 +~) o J U U3 J J J J

p2U _k_+~ p3U2 k] (0 +pk)2 . k1 ~x j2 (0 +pk)3 (kl ~x)2

Comparaison entre modèles continus et discontinus

La remarque faite plus haut est directement applicable pour ce qui concerne la liaison entre flux et concentration.

Pour comparer les résultats, nous calculerons les moments d'ordre zéro, un, deux et trois de la réponse impulsionnelle à un modèle con­tinu correspondant à une cinétique de premier ordre.

La réponse analytique a été donnée précédemment (L. Sine & J. P.

187

Agneessens partie III "Les solutions analytiques générales"). On en déduit les relations suivan tes

f; f dt = mo

1.00 tfdt=mo(O+pk)x o U

1.00

t 2 f dt = mo x 2(0 +pk)2 (1 +1 + 2 p2 U --L) (25)

o U2 P (0+pk)2 k1 x

1.00 t3 f dt = mO x 3 (0 +pk)3 {1 +Q +11 + (Q+12) p2 U2 k o U3 P p2 P p2 OD (0+pk)2 k1

+ ~ p 3 U4 Js..- } p2 02D2(0+pk)3 kr

On constate à nouveau que les expressions des moments d'ordre zéro, un et deux sont identiques si on postule

. {X = j /::::.x j = Ux = ~ (11)

2 DO 2

En introduisant ces expressions dans la dernière des relations (24) et en repassant aux flux, on obtient :

1.00 t3 f. dt= mO (0+pk)3 x3

[1 +2. +~ O. J U3 P p2

+2. (1 +1) p2 U2 L k + ~ p3 u4 k 1 p p (0 +pk)2 DO k1 p2 (0 +pk)3 D2 0 2 kr

(26)

On constate que les différences entre (26) et la dernière des rela­tions (24) sont d'autant moins marquées que Ie nombre de Peclet est élevé.

BIBLIOGRAPHIE.

Lapidus L. & Amundson N., (1952). Mathematics of adsorption in beds VI. The effects of longitudinal diffusion in ion exchange and chromatographic columns. J. Phys. Chem. 56, pp. 984-988.

Lindstrom F. & Boersma L., (1973). A theory on the mass transport of previously distributed chemicals in a water satured sorbing porous medium. 111. Exact solution for first order Kinetic sorbtion. Soil Science, vol. 115, pp. 5-10.

188

Molinarij. & RochonJ., (1976). Mesure des paramètres de transport de l'eau et des substances en solution en zone saturée. La Houille Blanche, NO 3/4, pp. 223-242.

Sine L. & AgneessensJ. P., (1978). Modélisation de la migration d'éléments dans les sols. I. Théories mathématiques en absence de réaction d'échange. 11. Détermination du coefficient de dispersion et de la porosité efficace. Pédologie, vol. XXVIII, pp. 349-388

Villermaux J., (1972). Analyse des processus chromatographiques linéaires à l'aide de modèles phénomé­nologiques. Chem. Eng. Sci., vol. 27, pp. 1231-1243.

Résumé

La comparaison entre modèles continus et discontinus décrivant la migration de solutés dans les sols est établie tout d'abord pour des modèles ou les réactions entre phase liquide et phase adsorbée sont linéaires, réversibles et instantanées et ensuite pour des modèles ou ces réactions relèvent d'une cinétique de premier ordre.

On démontre l'analogie entre modèles pour des nombres de Peclet suffisam­ment élevés, Ie nombre de Peclet du modèle continu étant égal au double du nombre de cellules du modèle discontinu.

Modelisatie van de migratie van chemicaliën in de bodem IV. Discontinue modellen

Samenvatting

Vergelijking van continue en discontinue modellen, welke de beweging van chemicaliënoplossingen in bodems beschrijven, wordt in de eerste plaats uitge­voerd voor modellen welke een lineair, omkeerbaar en plots adsorptie-isotherm vertonen; daarna voor modellen waarbij de adsorptiereacties een eerste orde cinetie aanduiden.

Gelijkheid tussen modellen wordt alleen aangetoond wanneer het aantal "Peclets" voldoende hoog ligt. Het aantal "Peclets"-.van een continu model is gelijk met het dubbel van het cellen aantal gebruikt in een discontinu model.

189

Modelization of the migration of chemicals in soils IV. Discontinuous models

Summary

Comparison between continuous and discontinuous modeis, describing move­ment of chemicals in soils, is fust elaborated for models presenting a linear re­versible and instantaneous adsorption isotherm; afterwards for models where reactions of adsorptions are of a first order kinetic.

Similarity between models is shown when the "Peclets" number is sufficiently high. The "Peclets" number of the continuous model is being equal to the double of the number of eells used in a diseontinuous model.

190

PEDOLOGIE, XXX, 2, p. 191-223, 15 fig., 4 tab., Ghent, 198,0.

THE DISTRIBUTION OF HEAVY METALS IN THE SOILS OF THE KEMPEN

1. Introduction

H. BOSMANS J. PAENHUYS

The natural distribution of the elements over the earth's surface is the result of multiple geochemical factors. By human activities such as extracting, handling and use of the metals and their chemical com­binations, this dispersion is now changing more strongly and more drastically than in the past.

If the living community and especially humans begin to suffer from the nuisance of these effects, we speak in terms of air-, water- or soil­pollution. If the cause of pollution is removed, air and river water will easily be cleansed of their pollutants by means of some kind of purific­ation cycle, but the soil, the rivermuds and the sea accumulate the whole pollution history in themselves as in a memory. This is not without lasting danger for the living beings which extract their food from these sources.

The Kempen soils, developed principally on strongly exhausted drift sands, were naturally quite poor both in mineral fertilizing salts and in trace elements. For more than a hundred years, this convenient­ly situated and cheap heathland has attracted the establishment of a whole series of non-ferrous metallurgy plants. These have provided work and led to population growth. But ore melting and other opera­tions have caused the sp reading of heavy metals as Zinc, Cadmium, Lead and Copper in a wide region. In addition the more recent lead pollution caused by the use of antiknock gasolines in cars must be borne in mind.

We must ask the question : what in fact is the normal original heavy metal content of the soil and where does pollution begin.

Bosmans H. - Prof. Dr. Ir., Paenhuys G. - Laboratorium voor Analytische en Mine­rale scheikunde, Landbouwinstituut, Katholieke Universiteit te Leuven, Kardinaal Mercierlaan 92, B-3030 Heverlee, België.

191

There is however no means of comparing two-hundred years old soil samples with the present day ones, but the study of local variations in their heavy metal content and a statistical evaluation of these variations have taught us much.

2. Method of extraction and analysis

We have chosen a method by which all available heavy metals are extracted from the soil sample. To do this it is unnecessary to dissolve the mineral grains of the soil as these consists nearly exclusively of quartz.

The soil sample is dried at 60 °c, ground fine and stripped of vege­table matter by passing it through a plastic sieve of 1.5 mm mesh. 10 g. of it are agitated during 2 h with 100 mI 0.5 N nitric acid at room temperature. The extract in 0.5 N nitric acid may af ter filtration be directly vaporised in an acetylene-compressed air flame and in this way the elements Zn, Cd, Pb and Cu may be determined successively by atomic absorption at the appropriate wavelengths.

The relative standard deviation of the determination itself proved to be 1.0 % and that of the extraction 1.6 %. Sometimes further dilutions with 0.5 N nitric acid, necessary mostly in the case of high Zn contents caused an even higher relative standard deviation, i.e. 3.8 %. However, these errors are negligible compared with the standard deviation found in sampling (see under). The element Cd was the only one which could not be determined in six samples. In these cases half of the value of the detection limit was assumed as a value for the statistical treatment.

Similar results can be obtained by differential pulse polarography with the dropping mercury electrode. In this method the four elements Cu, Pb, cd and Zn may be determined together in one run. Here the . 0.5 N nitric acid extract has to be brought to pH 3 by adding 0.25 N NaOH before taking a polarogram. In this way, the disturbing effect of the hydrogen wave is eleminated and precipitation reactions or complexation reactions with fulvic acid are still avoided. Although the · detection limits are of the same order of magnitude as with atomic absorption (for Cu and Pb they are even smaller) the labor and time necessary to neutralize the extract and to deoxygenate it with nitrogen, cause the polarographic method to be less favored for large numbers of determinations compared with the atomic absorption method.

The choice of 0.5 N nitric acid as an extractant was inspired by other research. J. De Venter (1977, Bodemkundige Dienst van België) agitates 10 g of soil with 100 mI 0.43 N nitric acid in order to deter-

192

mine Cu and Zn as t~ace elements in soils. Cottenie and coworkers (1970, Centrum voor Studie van de Scheikundige Vruchtbaarheid van de Bodem, Gent) agitate 10 g of soil with 50 mI 0.1 N or 0.5 N nitric acid. Lagerwerff (1973) in the U.S.A. us es 1 N hydrochloric acid as does Katalymov (1969) in the U.S.S.R.

In fact there is little difference in extraction efficiency between . nitric acid or hydrochloric acid if the solution is stronger than 0.01 N; this was found by P. Vanherwegen (.1977) in our laboratory in extrac­ting Zn from twelve Kempen soils. Extractions of longer duration and with stronger concentrations in acid gave no significant differences from our standard procedure on comparing their deviations with the deviations between double determinations. In this way the extraction with 6.09 N hydrochloric acid at its azeotropic boiling point (108.6 °C) during 12 hours in a soxhlet was compared tho the extraction with 6.09 N hydrochloric acid as weIl as with 0.5 N hydrochloric acid, 0.5 N nitric acid during 2 hours at 20 °C. Similar quantities of Zn, Cd, Cu and Pb were always found in the extract.

3. Sampling

To study the transport of heavy metals from the atmosphere to the soil, it seemed advisable to sample only the surface layers of the top soil. In fact the upper 5 cm of humus rich soil below the litter (i.e. the Ao of a podzol or disturbed podzol), of six profues of uncultivated strongly polluted and less polluted soils always contained the highest heavy metal content.

F or sampling we used a classic grassland probe which draws cylindri­cal cores with a diameter of 2.4 cm and a length of 6 cm (in every case about 40 g of soil). To minimize the effect of very loc al variations at every site, 12 to 16 samples were taken fr om the soil over a surface with radius of about 2 m. The subsamples were then mixed together to fonn one sample. Except in the beginning of the work we have taken a forest soil sample and a field or grassland soil sample at the same locality. The distance between these two samples varied mostly between 50 and 500 meters. At a few localities were there was only forest or field, we had to limit ourselves to a single type of sam ple. The forest soil samples were mostly found or preferably chosen in parcels with tall scotch pines, the soil of which could be assumed not to have been turned up for at least 20-30 years: Sampling of soils in alluvial valleys was also avoided as far as possible. We supposed that the undisturbed forest soil samples would give us also the most reliable information on the degree of accumulation of atmospheric

193

i': I •

100 100 m ,

.. '

Fig. 1.

Site map of the square grids GS, MS and KS (at Opgrimbie) used to compare the standard deviations of different sampling procedures .

metal pollution and this has proved to be the case. In fact field and grassland soils are regularly ploughed to the depth of the furrow, which causes a dilution of the surface pollution by de ph twise sprea­ding. In addition the administration of manure and fertilizers may also introduce heavy metals.

To exclude also the influence of traces of metal of any other origin than the original soil substrate and the supply from the atmosphere, we have tried to do the sampling as far from any inhabited area as possible. There an accumulation of metal traces is to be expected from such sources as paint pigments, metallic objects and any waste. Samples were also taken at 10 m or more from the parcellimits, to avoid borders of forests or fields which are too frequently used or still in use as illegal dumping grounds.

The history of a sampling place being difflcult to trace, a seriously deviating value found at some sampling point in spite of all these pre­cautions may always be interpreted as due to some recent digging, a stray galvanized bucket or brass cases from warfare etc. However the frequent occurence of high metal concentrations in neighbouring sampling points is without doubt due to atmospheric soil pollution.

194

To have an idea of the standard deviation observed with different sampling densities, we looked for a homogeneous flat area with a 'pre­sumed low metal pollution impact for a statistical study. In an oudy­ing part of the municipallity of Opgrimbie we found such a large homogeneous area grown with Scotch pines on the level plain of the Kempen plateau (96 ± 2 m above sea level). The soil map ofBelgium characterized this area as Zbg : dry sandy soil with a marked humus andfor ferruginuous B horizon.

With this aim, soil samples were taken within a limited radius on a square grid with 16 sampling points, on three different scales as follows (fig. 1).

In the first trial (small scale statistics (KS)) 16 samples within 2 cm radius at 2 m from each other.

In the second trial (medium scale statistics (MS)) 16 samples within 20 cm radius at 20 m from each other.

In the third trial (large scale statistics (GS)) 16 samples within 2 m radius at 200 m from each other.

For comparison with our practical standard method of sampling we used field statistcs (VS/1) i.e. 12 sampling points with 2 m radius at about 4 km from each other in a selected region of the southern borderland of the Limburg Kempen (the area around Zutendaal).

Also a second sampling area was selected for comparison (VSf2) i.e. 15 sampling points with 2 m radius at about 5 km distance trom each other in the N.W. of the Kempen (the area around Kalmthout).

This second sampling area around Kalmthout was selected af ter­wards for this trial when it had been noticed that soils from this part of the Kempen had the lowest metal concentrations and thus pre­sumabily also the lowest pollution.

Typical of this second area of field statistics, are the practically equal Cu and Cd contents, but the stililower contents of Zn (half as much) and Pb (one third less), compared with the first selected area in the S. E. of the Kempen (area around Zutendaal). This first area of reference is clearly still under the influence of the industries further north, which spread Zn and Pb.

From these trials it appears that for the four metals determined in a homogeneous area with little pollution, the variation expressed as relative standard deviation is of the order of 50 %, if the sampling points were at 4 or 5 km distance and at 200 m distance. Only if the distance between the sampling points and also the radius for sampling is still further reduced to 20 m (20 cm radius) and 2 m (2 cm radius) is the relative standard deviation lower, but still 30 %. The variation in

195

Table 1

For each element are given : mean ± standard deviation and (relative standard deviation %)

Small sc ale statistics (KS) (ö = 2m) 16 samples

Zn cd Pb Cu 16.3 ± 8.3 0.30 ± 0.11 42.5 ± 12.6 3.20 ± 0.77

(51 %) (37%) (30%) (24 %)

Medium scale stat; stics (MS) (ö = 20 m) 16 samples

Zn Cd Pb Cu 13.5 ± 3.6 0.24 ± 0.12 48.2 ± 11.8 3.98±0.75

(27%) (50%) (25%) (19 %)

Large scale statistics (GS) (6 = 200 m) 16 samples

Zn Cd Pb Cu 27.8 ± 10.5 0.43 ± 0.22 59.6 ± 28.2 4.30 ± 1.80

(38%) (51 %) (47%) (42%)

Field statistics (VS/1) (6 ~4 km) 12 samples

Zn Cd Pb Cu 20.0 ± 9.4 0.30 ± 0.14 45.1 ± 24.3 2.99 ± 1.42

(47%) (47%) (54%) (48%)

Field statistics (VS/2) (6 ~ 5km) 15 samples

Zn cd Pb Cu 10.5 ± 4.2 0.34 ± 0.12 31.2 ± 14.5 2.8 ± 1.7

(40%) (35%) (47%) (61%)

organic matter or humus content of the soil which is supposed to fix the metal may well be one of the factors responsible for this va-iation.

If we consider the values of metal concentration in soils of the least polluted area (around Kalmthout) as a guidance for nearly unpolluted forest soil on Kempen sandy soil (Ao horizon), we may write down the following normal metal concentrations in forest soil :

5-15 ppm Zn, 0.15-0.45 ppm Cd, 15-45 ppm Pb, 1.5-4.5 ppm Cu. The lead content may seem high, but as we shall see, the lead content in a forest soil was, in the mean for the whole Kempen area, always abou t twice as high as in a field or grassland soil.

4. Results

In all, about 225 sites were sampled i.e. 224 forest soils and 214 field or grassland soils over the Belgian Kempen (5 points were lying

196

J

~

...0 -.....]

23

··_--z/?~

\ ........ # ., ..... , •••

SAMPLlIIKj LOCALITIES WITH NR G \V

NON - FERROUS METALINDUSTRIES

TOPOGRAPHICAL MAP SHEE TS

Fig. 2.

* ~ G.EEG]

2 4 6 8 10 Km 20 ......... ...,..., ..... 9

Map of the Belgian Kempen divided in map sheets with the sampling localities and their number.

~

18

26

over the Dutch border) covering about 4 000 km 2 (fig. 2). On 213 sites a sample of forest soil and of field or grassland soil could be taken at areasonabie distance. This makes about one sample every 18 km 2 which gives in the case of a triangular net at equal distances, a mean distance of 4.5 km between the sampling sites. However the density of the samples was not evenly distributed. Less sampling was done in the West and on the South border, which, as progressive work demonstrated, we re not as heavily contaminated as the Central and the N orthern parts. This, together with the somewhat arbitrary limits of the area has to be taken into account in considering the means and the distributions of the analytical results.

Table 2 gives the heavy metal content in p.p.m. in the soil samples with their site number and vegetation (see note). The frequency distribution of all analytical values for each of the four elements both in forest soil samples and in field or grassland samples looks very asymetrical. The steep rise in metal content of soils in the vicinity of pollution sources affects the analytical values and in the logarithmic form, gives a practically normal frequency distribution. This distribu­tion is very symmetrical in the case of forest soil samples (fig. 3 and fig. 4).

Table 2

Content of heavy metals in p.p.m. (mg metal/kg soU)

Forest sqil samples Field or grassland soil samples

Locality Zn Cd Pb Cu Zn cd Pb Cu nr. veg. (ppm) (ppm) (ppm) (ppm) veg . . (ppm) (ppm) (ppm) (ppm)

1 L 84,3 . 1,50 48,9 8,0 2 H 15,7 0,50 30,5 1,0 3 H 12,6 0,40 15,7 0,7 4 D 20,6 0,44 21,8 3,5 A 16,1 0,30 14,2 3,5 5 D 12,1 0,20 22,7 5,7 W 13,4 0,21 9,6 5,3 6 D 2,0 0,15 25,4 70,3 A 21,2 0,69 24,1 41,4 7 D 16,9 0,34 47,2 82,2 A 10,3 0,12 14,2 9,0 8 D 29,8 0,35 58,5 32,3 9 D · 68,4 0,79 64,1 28,1 A 41,0 0,50 23,2 9,5

10 D 18,1 0,15 39,5 17,1

11 D 8,4 0,12 20,8 4,9 A 8,0 0,15 6,4 2,9 12 D 15,4 0,18 33,8 4,5 W 21,4 0,20 6,9 6,9 13 D 16,8 0,36 23,9 5,1 w 27,2 0,36 16,9 5,0 14 D 12,4 0,28 22,9 3,5 w 29,2 0,26 10,4 13,3 15 D 40,6 0,53 60,5 12,4 A 19,4 0,40 33,9 9,5 16 D 8,4 0,02 22,3 2,6 W 24,1 0,34 15,8 2,5

198

17 D 50,7 0,69 63,0 11,6 A 17,6 0,47 13,7 4,4 18 D 5,4 0,02 28,9 4,2 A 28,9 0,58 17,7 5,8 19 p 79,6 1,28 46,6 18,4 W 41,9 0,60 28,1 12,3 20 84,9 1,80 105,8 28,3 A 18,9 0,44 11,9 3,2

21 D 15,3 0,42 30,3 8,2 W 20,9 0,31 14,6 6,9 22 D 7,0 0,20 21,1 4,8 23 D 35,3 0,56 55,7 8,3 W 61,6 1,04 35,8 6,8 24 D 17,4 0,47 21,7 4,2 G 19,1 0,50 15,2 3,7 25 D 5,6 0,19 15,9 3,9 A 15,9 0,25 10,0 2,8 26 28,5 0,50 53,2 9,8 39,5 0,83 23,3 3,2 27 D 16,4 0,34 49,3 5,0 G 75,6 1,09 84,1 17,6 28 D 42,4 0,83 88,7 10,7 W 60,1 1,08 52,2 9,5 29 p 79,9 3,43 35,3 6,9 VI 136,7 6,79 58,5 9,6 30 D 17,0 0,21 37,4 2,8 W 20,7 0,34 16,7 1,4

31 L 24,0 0,33 48,7 4,1 W 59,5 0,38 13,9 27,1 32 D 28,9 0,48 81 ,8 9,5 A 18,9 0,48 18,6 3,2 33 D 20,1 0,26 47,7 6,1 A 52,9 0,63 19,9 5,7 34 D 69,1 1,69 125,9 11,4 A 30,5 0,73 19,8 1,5 35 D 118,9 2,06 155,6 13,1 A 54,0 1,05 27,2 11,5 36 D 28,2 0,52 42,7 3,8 A 43,1 0,69 18,5 9,2 37 300,5 4,80 409,0 34,1 A 96,1 1,63 34,8 4,0 38 23,0 0,41 86,5 7,8 39 460,1 11,10 555,5 20,6 A 68,8 1,95 75,0 6,7 40 D 27,1 0,46 96,3 12,3 W 66,6 0,65 42,9 7,7

41 D 10,3 0,22 30,6 3,5 A 22,3 0,36 16,2 3,6 42 D 31,3 0,75 70,4 5,6 A 23,9 0,49 11,1 0,9 43 D 20,4 0,50 74,3 5,0 44 15,3 0,35 62,4 5,8 A 62,8 0,81 52,8 12,3 45 27,8 0,86 46,9 4,0 W 72,5 1,12 48,8 6,9 46 D 60,9 0,77 82,5 7,5 A 47,5 0,77 26,9 4 ,1 47 D 50,1 0,80 115,0 10,1 A 15,8 0,39 31,5 5,7 48 D 25,3 0,54 68,4 8,6 A 144,0 2,12 36 ,7 6,7 49 D 117,4 1,42 103,1 7,8 A 48,3 0,79 18,3 1,5 50 L 81,1 0,93 76,9 7,8 A 95,8 1,06 21,4 6,5

51 L 258,6 4,25 226,8 18,7 A 75,0 0,99 18,4 5,1 52 14,0 0,24 8,9 0,9 A 53,4 0,78 18,2 4,3 53 D 80,8 1,25 78,8 11,3 W 48,2 0,58 19,1 19,3 54 D 63,2 0,82 114,1 6,1 A 19,1 0,37 18,1 2,2 55 D 26,6 0,43 47,5 3,9 A 12,2 0,36 21,3 2,9 56 D 11,4 0,15 37,8 2,4 A 20,6 0,29 13,1 5,2 57 D 5,5 0,04 17,2 0,9 W 28,7 0,44 16,7 1,3 58 D 4,8 0,05 18,9 0,9 W 25,1 0,51 23,9 1,5 59 25,6 0,31 50,3 4,1 W 9,8 0,29 23,6 2,1 60 D 56,5 1,01 87,9 6,1 A 16,6 0,38 12,8 2,5

61 D 10,4 0,21 10,0 0,6 A 11;2 0,26 8,0 1,0 62 D 13,3 0,18 87,5 2,4 A 8,5 0,22 13,9 1,2 63 D 12,3 0,19 30,5 1,7 A 24,1 0,26 15,9 3,0

199

t'

64 D 9,6 0,13 30,0 1,2 W 20,0 0,35 21,6 2,3 65 D 28,2 0,61 78,1 4,6 66 D 163,9 4,26 44,8 32,2 A 74,4 2,07 27,5 3,7 67 L 21,5 0,29 45,1 3,3 A 17,8 0,23 9,1 2,0 68 D 26,9 0,44 68,6 5,0 W 61,8 0,88 38,2 20,0 69 D 14,0 0,15 36,5 3,5 A 23,2 0,26 14,2 8,8 70 D 14,4 0,20 20,9 2,2 A 16,2 0,34 23,8 3,6

71 L 40,3 0,58 58,8 10,5 A 11,1 0,41 16,7 3,0 72 L 32,1 0,40 43,3 7,9 A 27,5 0,55 20,4 4,2 73 L 18,0 0,12 29,3 12,6 A 9,6 0,26 13,3 2,1 74 D 27,4 0,19 36,8 11,4 W 16,7 0,14 9,5 2,6 75 D 17,2 0,33 37,9 50,2 27,1 0,48 23,4 26,8 76 D 6,9 0,10 25,3 9,8 G 14,0 0,29 19,3 6,2 77 D 12,1 0,09 32,5 5,0 A 13,2 0,23 15,2 2,8 78 D 10,3 0,13 29,8 5,5 G 6,2 0,09 13,2 1,9 79 L 59,0 1,19 104,8 17,0 19,6 0,43 19,3 4,1 80 L 27,6 0,55 79,3 10,4 W 46,0 1,20 51,4 14,1

81 D 9,4 0,13 49,1 9,2 W 19,7 0,48 21,3 4,6 82 D 11,6 0,14 41,6 8,9 W 12,5 0,16 17,7 5,2 83 D 5,8 0,18 28,9 9,1 G 29,9 0,36 27,4 6,9 84 D 7,0 0,14 26,0 9,8 A 14,8 0,21 15,2 7,4 85 D 69,3 0,92 105,7 26,9 W 12,3 0,30 13,9 5,4 86 D 20,4 0,32 45,4 13,9 87 D 67,9 0,83 91,7 40,6 W 66,1 0,78 39,5 22,6 88 D 28,3 0,46 45,8 9,2 A 13,9 0,38 15,7 2,8 89 D 19,2 0,26 39,8 9,Î A 16,8 0,25 24,1 4,6 90 D 15,8 0,17 90,4 30,2 A 12,6 0,13 10,7 6,4

91 D 20,5 0,28 46,4 13,2 W 51,8 0,73 39,1 13,1 92 L 9,1 0,27 26,4 5,8 W 74,9 1,3 40,9 16,1 93 P 24,4 0,66 60,9 15,8 G 15,5 0,33 19,7 6,5 94 34,2 0,52 31,9 4,6 W 33,5 0,58 21,6 4,2 95 D 13,9 0,17 24,0 3,2 A 16,7 0,21 10,3 6,3 96 D 31,2 0,46 60,9 6,5 W 13,2 0,30 15,3 2,2 97 D 4,6 0,06 10,5 1,3 W 8,1 0,13 11,2 3,9 98 D 15,3 0,24 27,5 2,4 A 17,2 0,24 6,7 4,9 99 p 82,9 2,14 55,2 10,1 G 30,6 0,67 17,8 2,8

100 D 23,7 0,39 35,4 5,2 W 29,0 0,43 15,2 4,1

101 L 15,7 0,42 34,6 6,6 24,2 0,62 40,4 7,8 102 L 13,3 0,26 38,1 4,4 16,8 0,34 24,5 7,4 103 L 26,5 0,39 47,1 11,3 A 16,2 0,40 23,7 5,9 104 D 2,9 0,06 17,5 2,5 W 27,6 0,96 29,4 4,7 105 D 12,7 0,20 40,8 6,3 A 11,2 0,27 12,7 2,0 106 D 9,0 0,24 40,2 6,3 A 15,5 0,36 28,9 8,8 107 D 3,1 0,05 18,3 2,9 W 23,1 0,54 31,1 10,8 108 P 43,1 1,37 84,9 10,7 W 26,9 1,00 77,5 5,7 109 L 16,9 0,40 49,0 5,2 W 40,7 0,50 105,2 33,3 110 LI 8,9 0,36 14,0 1,5 W 23,3 0,04 22,4 3,8

200

I

'I

111 D 7,2 0,33 30,7 1,4 W 9,3 0,31 11,4 1,4 112 D 3,9 0,25 9,7 0,3 A 11,9 0,18 7,9 3,2 113 L 9,1 0,32 15,9 0,9 W 12,0 0,43 12,8 0,9 114 D 2,7 0,13 9,4 0,5 A 10,0 0,24 8,7 1,4 115 D 13,5 0,30 19,5 1,6 W 20,7 0,47 27,1 1,9 116 L 12,5 0,40 35,0 2,8 W 14,4 0,46 18,3 3,7 117 L 11,9 0,22 34,5 4,6 W 24,9 0,25 10,7 0.7 118 D 16,3 0,23 30,3 2,8 W 57,5 0,94 26,9 2,5 119 D 18,9 0,24 40,6 3,5 G 14,2 0,38 13,9 1,9 120 D 23,3 0,39 72,6 4,5 A 25,0 0,59 12,6 1,6

121 D 48,6 0,57 45,9 3,9 A 15,0 0,41 9,6 1,4 122 L 34,7 0,41 41,9 3,9 G 16,4 0,32 13,1 2,8 123 L 51,2 0,78 102,6 6,5 A 28,9 0,51 14,6 5,0 124 P 97,6 1,41 38,9 4,2 W 306,6 3,20 139,3 17,6 125 D 14,3 0,28 46,4 2,5 126 D 16,8 0,17 39,3 2,2 W 25,4 0,37 18,5 3,1 127 P 120,3 1,00 58,7 14,2 W 45,1 0,72 41,6 16,3 128 D 31,3 0,46 68,3 5,6 A 16,9 0,28 16,1 2,5 129 D 5,6 0,00 20,2 1,4 A 21,8 0,47 14,2 2,6 130 D 5,6 0,07 20,6 1,5 A 12,5 0,25 13,5 1,4

131 D 13,8 0,24 44,9 4,6 A 36,1 0,71 21,6 2,9 132 L 8,8 0,29 56,0 3,1 W 11,3 0,35 20,8 2,2 . 133 L 10,5 0,66 43,6 3,2 W 18,4 0,44 43,4 2,2 134 D 16,3 0,41 30,6 3,6 A 13,0 0,69 33,8 2,6 135 D 7,0 0,32 40,5 3,4 W 19,3 0,61 28,1 3,7 136 L 14,7 0,45 41,7 5,4 W 1,5,9 0,41 32,8 4,8 137 p 18,3 1,22 40,9 3,7 W 14,4 0,92 40,7 5,5 138 D 10,7 0,45 67,1 10,1 A 18,9 0,78 51,5 11,7 139 L 11,3 0,20 68,2 12,9 W 13,6 0 ,51 29,2 5,6 140 D 7,0 0,02 26,6 2,7 43,5 0,47 25,0 3,7

141 D 28,2 0,48 96,6 9,9 62,2 1,38 64,7 7,9 142 D 6,7 0,02 30,8 2,3 W 106,7 1,77 91,0 5,3 143 D 7,4 0,02 23,0 4,0 W 75,9 1,22 43,4 8,8 144 D 19,2 0,34 37,3 13,9 W 29,0 0,58 23,6 8,2 145 D 9,8 0,02 24,5 4,7 W 24,7 0,34 19,4 7,4 146 P 34,6 0,69 24,8 5,3 A 17,5 0,44 17,2 7,5 147 D 10,8 0,02 22,9 6,8 A 9,0 0,02 8,2 2,5 148 D 21,9 0,48 26,4 2,8 A 14,4 0,09 8,9 2,8 149 L 23,5 0,26 21,1 2,9 W 42,3 1,20 35,8 6,5 150 D 4,8 0,09 17,1 1,7 A 6,1 0,10 13,5 2,4

151 D 11,3 0,27 23,7 1,9 A 12,8 0,21 16,0 4,3 152 L 22,8 0,56 54,8 3,3 A 12,0 0,25 14,5 2,0 153 L 21,9 0,32 21,8 2,5 W 10,5 0,20 13,8 1,6 154 L 38,0 0,49 44,5 4,2 39,7 0,74 27,0 2,3 155 D 16,1 0,24 33,4 2,5 A 2J,2 0,28 17,5 2,9 156 p 28,6 0,29 79,7 4,9 W 46,2 0,80 37,8 9,3 157 D 31,5 0,44 57,7 3,5 A 23,0 0,40 22,6 4,8

201

158 D 17,6 0,39 56 ,0 5,8 10,4 0,30 12,4 1,0 159 D 18,5 0,43 56,3 5,2 W 34,2 0,74 24,7 2,9 160 D 19,1 0,43 49,8 8,8 W 32,8 0,58 19,2 4,4

161 D 22,9 0,79 137,8 14,2 A 82,4 1,79 58,4 6,8 162 D 46,9 1,30 118,6 10,7 A 15,6 0,69 23,2 2,5 163 D 148,9 2,45 342,8 24,7 A 66,4 1,16 34,4 7,2 164 D 41,9 1,01 61,1 8,7 A 127,6 1,97 54,1 9,4 165 D 228,5 3,72 354,8 28,6 G 76,1 1,14 354,8 5,4 166 D 142,0 1,96 230,2 40,9 A 45,1 0,80 19,0 2,6 167 D 116,4 1,42 134,4 10,5 A 14,3 0,23 17,2 1,9 168 D 137,4 1,36 130,5 10,8 W 35,4 0,63 19,0 1,9 169 D 41,7 0,51 69,5 14,9 A 100,0 0,62 37,7 12,9 170 D 16,9 0,33 53,1 7,3 G 37,3 0,48 22,3 4,4

171 D 30,2 0,30 44,7 6,9 G 26,2 0,21 16,2 9,9 172 D 12,6 0,14 25,8 7,3 15,3 0,20 12,8 7,0 173 D 10,5 0,21 31,9 13,2 A 7,1 0,20 10,1 2,7 174 D 10,6 0,22 47,6 11,4 G 9,2 0,29 15,6 4,6 175 D 17,2 0,28 57,3 17,1 W 8,2 0,40 15,3 4,8 176 D 42,8 0,48 87,0 38,8 W 13,2 0,48 24,8 5,1 177 D 8,3 0,11 22,1 11,2 A 8,6 0,30 17,0 6,5 178 D 11,4 0,27 48,9 37,4 A 3,8 0,11 6,6 5,9 179 D 14,5 0,38 30,5 79,8 W 26 ,4 1,02 23,5 39,7 180 D 4,2 0,09 48,8 26,4 G 4,2 0,12 14,7 8,2

181 D 7,8 0,15 19,6 13,9 W 18,5 0,37 19,8 11,0 182 L 35,9 0,88 49,6 67,1 W 9,8 0,28 15,7 25,6 183 D 14,9 0,37 42,3 28,8 A 10,3 0,21 14,3 7,5 184 D 19,4 0,35 53,5 34,3 W 29,2 0,25 17,9 18,2 185 L 26,2 0,34 76,6 5,5 W 45,9 0,78 27,1 17,9 186 D 33,1 0,51 68,9 20,8 W 77,4 0,47 19,2 17,9 187 D 43,1 0,46 90,1 30,8 A 26,6 0,27 ]4,1 5,9 188 D 23,4 0,40 47,3 10,5 23,1 0,39 21,9 4,5 189 D 63,7 0,84 185,3 146,3 W 244,8 1,78 164,2 117,4 190 L 50,3 0,79 126,2 25,7 W 27,1 0,43 101,5 13,8

191 D 7,8 0,15 28,8 3,9 W 9,1 0,22 13,6 3,1 192 D 40,0 0,81 87,7 15,2 W 18,6 0,50 15,6 3,1 193 D 9,6 0,18 24,9 4,2 A 11,3 0,15 6,9 1,6 194 D 27,8 0,31 34,6 4,7 A 40,5 0,20 10,2 17,0 195 D 17,2 0,54 40,9 8,8 A 11,5 0,18 9,2 2,6 196 D 39,9 0,54 78,6 21,9 W 68,6 0,43 21,2 8,5 197 D 34,2 0,60 77,7 17,7 W 50,4 0,55 21,7 5,7 198 D 20,8 0,43 60,4 11,5 G 17,5 0,35 13,0 3,5 199 D 39,9 0,80 86,9 16,2 W 39,1 0,62 20,5 2,8 200 D 37,8 0,56 45,6 11,6 W 19,3 0,34 29,5 7,2

201 D 23,9 0,56 74,1 36,7 A 19,5 0,42 10,9 3,8 202 D 53,5 0,84 99,1 30,3 G 14,9 0,49 19,8 3,5 203 L 32,6 0,70 85,5 10,0 W 29,1 0,68 33,3 5,3 204 D 11,8 0,21 80,8 6,9 A 18,1 0,43 14,8 5,4

202

205 D 206 D 207 208 D 209 D 210 L

211 D 212 D 213 D 214 D 215 D 216 D 217 D 218 D 219 D 220 D

221 D 222 D 223 D 224 D 225 D

Note:

38,7 1,12 122,6 10,8 0,19 34,1

40,8 0,47 132,2 24,8 0,41 47,1

112,0 1,22 132,9

44,8 0,93 97,6 26,2 0,81 62,9 68,4 1,04 192,2

260,8 2,60 151,7 38,7 0,45 31,5 43,5 0,51 60,9 50,5 0,74 72,6 98,0 1,27 131,3 29,6 0,50 76,1

223,8 3,49 83,4

38,0 0,76 53,3 50,0 0,88 119,4 24,1 0,40 49,0 69,2 1,56 86,3 51,6 1,19 131,4

F orest soil samples: D : Scotch Pine (pinus ) P : Poplar

8,5 7,8

12,3 10,6 17,5

17,3 14,6 28,9 16,5

2,8 3,9 6,4 8,9 6,6

10,6

7,5 13,2 4,1 6,7

12,6

L : Other deciduous trees

W 107,8 1,61 43,7 21,3 A 8,9 0,30 12,7 3,2 G 15,3 0,22 19,0 11,3 A 64,1 0,44 28,7 9,4 A 20,8 0,19 16,3 9,2 W 68,6 0,64 41,6 9,6

W 43,5 0,86 28,5 11,3 W 89,7 1,43 61,9 11,4 W 101,0 1,42 74,3 8,9 A 164,6 1,63 25,8 9,8 A 53,5 0,74 12,2 2,1 A 17,2 0,20 9,8 4,6 W 21,7 0,20 4,7 4,3 A 25,7 0,61 14,2 1,9 A 13,9 0,31 13,5 2,3 G 116,3 1,57 43,2 11,5

W 226,9 2,67 37,7 5,3 W 91,8 1,01 33,6 10,5 A 16,3 0,22 10,5 2,3 G 26,3 0,60 18,4 3,7 G 24,6 0,20 13,2 13,4

Field or grassland soil samples: A : Field G : Raygrass W: Past\lre.

As M. J. Buchauer (1973) has shown for two isolated zinc smelters in Palmerton Pa (U.S.A.), the content of each of the heavy metals in the Ao horizon decreases logarithmically with the distance from the pollution source. At a distance of about 20 km this logarithmic de­crease get lost in the horizontal of the mean value of natural metal content of the soil. This logarithmic or geometrical decrease of metal content around apollution source agrees with an increase in covered surface proportional to the square of the distance from the source. Taking into account the scattered implantation of many non-ferrous metal industries active at different periods in the studied area, such a relation is difficult to controll here.

In contrast to the relative arithmetic standard deviations for metal contents in the soil samples of our reference areas with little or no pollu tion, lying around 50 %, we find here for the whole Kempen area a relative arithmetic standard deviation of about 100 % or more. Numerous high values due to pollution are Without doubt responsible for the stronger dispersion and its more asymetrical form by consider- . ation of the whole sam ple lot.

203

Pb - 8

80 Pb - 8

80

.0 .0

20 20

150

Cu -8 80 Cu -8

.0

20

ppm .a

Zn -8 Zn -8

80 80

.0 .0

20 20

ppm

Cd -8 80 Cd -8 80

20

ppm

Fig. 3.

Frequeney distribution for forest soils following respeetively an arith­metie and a logarithmie seale for their heavy metal eontents

204

80

'0

20 f-

80

20

80

.0

20

Fig. 4.

Pb -A

50 100

Cu - A

20

Zn - A

Cd -A

Pb - A

80

.0

20

158 ppm

Cu -A 80

2 1011 ppm 3

Zn -A '0

40

20

150 ppm

Cd - A .0

20

ppm 4

Frequency distribution for field or grassland soils following res­pectively an arithmetic and a logarithmic sc ale for their heavy metal contents. 205

Table 3

Survey of metal contents in the studied soil samples For the four elements are respectively given : - the arithmetic mean X - the arithmetic standard deviation ± Sx - the median m - the mean of the logarithms of the analytical values log X - the standard deviation of these logarithmic values ± Slog X

F orest soil samples

Zn cd Pb -X 37.5 0.65 63.4

± Sx 52.2 1.00 61.5

m 21.9 0.40 47.3

logX 1.363 -0.415 1.689

± Slog X 0.405 0.454 0.297

Field or grassland soil samples

Zn Cd Pb -X 36.1 0.61 26.8

± sx 38.8 0.63 30.5

m 23.0 0.43 19.0

log X 1.409 -0.346 1.320

± Slog X 0.339 0.329 0.271

Cu

11.5

15.4

6.9

0.847

0.429

Cu

7.2

9.8

4.8

0.695

0.351

If we compare the forest soil contents with the field or grassland soil contents, we see that the mean values and the medians for Zn and Cd have similar values but for Cu these values are systematically higher in forest soils, and for Pb the mean and the median are even more than twice as high in forest soils compared to these in field or grassland soils.

This deviating behaviour of Pb in forest soils which we noticed fr om the earliest series of determinations of soil pairs was interpreted first as coming fr om the effect of atmospheric pollution hy vehicle traffic using antiknock gasolines. The foliage of the trees, catching an important portion of the dispersed lead from the atmosphere, will by the fall of leaves or needles enrich the surface layer of the soil relative­ly more in lead than in the other metals, because vehicle traffic has increased so tremendously in the last twenty years. On the contrary

206

the fraction fallen on a field or grassland soil surface wili" on ploughing be distributed over the whole furrow depth.

This may be the most obvious explanation, but we have to take in­to account also the behaviour of the different metals with respect to humus, whieh in our Kempen soil contributes over 90 % to the cation exchange capacity. In our laboratory P. Vanherwegen (19772) has shown for 14 different soil samples from the Kempen that, af ter 2 hours of agitation with equimolar solutions of Zn, Cd, Pb and Cu (0.3 mmoie) at a pH 3.5, these ions are not fixed to the same extent. The exchange selectivity Pb> Cu ~ cd> Zn thus found is in agreement with the stability of their ion complexes with diearboxylic anions where the carboxyl functions are ortho substituted on aromatie sub­stances (e.g. phthalic acid), as found by Yasudo, Yamasaki and Ohtaki (1960).

Such ortho substituted carboxyl functions are to a great ex tent responsible for the ion exchange capacity of the humus, as can be con­cluded from the mean composition of a soluble humus fraction as e.g. the fulvic acids (Schnitzer and Desjardins 1962). Hence another ex­planation for the fact that humus rich forest soils may fix much more Pb and more Cu, irrespective of the origin of the metals. Nevertheless J. Stevensson (1976) has found a complex stability Cu> Pb ~ cd> Zn by potentiometric titration of isolated humie acids, Cu being linked somewhat stronger than Pb.

5. Correlations

Having at our disposal a large number of analytical results, we have also calculated the correlation between the content of each pair of metals in the forest soil samples and in the field or grassland soil samples. Each series gives six correlations for the four metal contents. Finally we have calculated the correlation between every metal con­tent in a forest soil sample and its content in a corresponding field or grassland soil from the same locality.

These correlations were calculated both on the arithmetic values and on the logarithmic values of the metal contents. Taking into account the lognormal distribution in every lot of samples, we con­sider the correlation calculations on the logarithmic values as more meningfull.

In table 4 the correlation coefficients are given as wen for the arithmetic values (RR) as for the logarithmic values (LR).

207

Table 4

Correlation coefficients between different metal contents on the arithmetic scale (RR) and on the logarithmic scale (LR) in the same soil type; and correlation coefficients of the same metal in soils of different type at the same locality

Forest soil samples n = 224 r = 0.171

Zn Cd Pb

Cd RR 0.93 LR 0.86

Pb RR 0.83 RR 0.80 LR 0.79 LR 0.70

Cu RR 0.20 RR 0.18 RR 0.32 LR 0.50 LR 0.44 LR 0.64

Field or grassland soil samples n = 214 r = 0.175

Zn Cd Pb

cd RR 0.75 LR 0.80

Pb RR 0.52 RR 0.43 LR 0.66 LR 0.72

Cu RR 0.46 RR 0.22 RR 0.38 LR 0.48 LR 0.33 LR 0.50

Comparison of forest soil with field or grassland soil samples n = 213 r = 0.175

RR 0.38

LR 0.50

RR 0.47

LR 0.46

~ (Xi - X) . (Yi - Y) R = --=-i __________ _

Y 4 (xi - X) 2 . 4 (Y i - Y) 2 1 1

RR 0.42

LR 0.39

RR 0.72

LR 0.51

In all cases a distinct positive correlation trend was found. To have only a 0.5 % probability for unilateral transgression in the case of n = 224 (forest soil) samples, the correlation coefficient has to be 0.1 71, and for n = 214 (field or grassland soil) samples, and also for n = 213 (samples from a single locality) R has to be 0.175.

It is even more interesting to compare the extent of correlation or the variance about regression between the different metal contents.

208

We then see that for the forest soil samples the cd content is very strongly correlated with the Zn content,and the Pb content is also strongly correlated with the Zn content and with that of Cd, but the correlation of the Cu content with those of Zn and Cd seems to be rather weak and is only somewhat better with the content of Pb.

F or the field or grassland soil sam pIes we find a similar correlation tendency between the different metal contents, altough somewhat less pronounced. This is probably linked to the thinning effect by ploughing and to the influence of added fertilizers etc. typical for such soils.

We also ob serve areasonabie correlation between the contents of the same metal in a forest soil and a field or grassland soil fr om the same locality.

In fig. 5, 6 and 7, we have represented graphically the cloud of correlated values on the logarithmic scale together with the two cal­culated regression lines for the metal pairs Cd-Zn, Pb-Zn and Cu-Zn in forest soils.

As expected one sees that the lower the correlation coefficient, the higher the angle between the two regression lines.

A positive correlation between the different metal contents in a soil will, among other factors , be connected with the humus content and its fixation capacity for metals.

Cd -B

o. ~

- 1,5

0.5 1.5

Zn -B 2 log ppm 2.~

Fig. 5.

Correlation diagram with regression lines for Cd and Zn contents (on log scales) in forest soils.

209

2.5

E Q. Q.

1.5

0 .5

Pb-B

L R.o.a

0 . 5

Cu-B

0. 5

Zn-B 1.5 2 log ppm 2.5

Zn-B 2 log ppm 2.5

Fig. 6.

Correlation diagram with regression lines for Pb and Zn contents (on log sc ales) in forest soils.

Fig. 7.

Correlation diagram with regression lines for Cu and Zn contents (on log scales) in forest soils.

This is surely not the only reason because the correlation is not equally strong for every metal pair as is seen in the coupling of Zn with Cd and also with Pb, but nearly not with Cu. That Zn and cd contents are so strongly correlated follows from their chemical similarity which not only shows up in their fixation and mobility be­haviour in soil, but also in their liberation together in the atmosphere

210 I

I

J

on the processing of their ores in which they occur together. Altough Pb shows a marked difference fr om Zn and Cd in some chemical aspects e.g. in their Hxation and mobility in soils, similarity in other properties causes the ores to occur together so that their processing with the resulting losses in the atmosphere occurred from the same industrial sourees explaining in this way the correlation of high Pb contents with similar Zn and Cd contents in soil samples. The fact that Cu with respect to its fixapility on humus approaches best the behaviour of Pb and nevertheless only a weak correlation hetween their respective metal contents in soils is ohserved, depends clearly on the fact that as with the metals in the ores, also the processing of copper ores and scrap, and the copper metal refining on one hand, do not go together in the Kempen area with those for Zn, cd and Ph on the other hand.

6. Spatial distribution

On a map of the Kempen any of the four metal contents is repre­sented in the different localities separately for the two types of soil sampled hy us, following a suited sealing in classes, taking into account the log normal distrihution. The symhols showadenser shading for each metal content class twice as high as the preceding one, forming in this way a log2 scale suited to each metal. Care was heing taken that the median of every metal content lay approximately in the middle of the middlemost class of the five class scale.

Large existing or former non-ferrous industries are indicated with an asterisk. Looking at the maps for forest soils for every metal, we observe that high Zn contents ,occur in a sickle-shaped zone over the Northern half of the Province of Limburg. Cd contents show a similar distrihution. Pb contents are high in the Northern part of the Provinee of Limburg and also in the North East of the Provinee of Antwerp. ' High Cu contents on the other hand are striking in the East of the Province of Antwerp i.e. around Herentals and Turnhout hut also around Lommel (fig. 8, fig. 9, fig. 10, fig. 11).

The maps for metal contents in field or grassland soils show a simil­ar, but somewhat less clear picture. (fig. 12; fig. 13, fig. 14, fig. 15).

To obtain a more objective and simple survey for the metal distd.bu­tion in the Kempen, we have calculated the mean metal content from the individual metal contents for forest soils situated on a 1/8 th sheet of the 1/25,000 topographic map giving up one value for every 80 km 2. These values are independent of the sampling density and also less dependent on accidental higher or lower values at one point.

211

o 2 4 6 8 10 Km 20 ~ lo000ooi lo000ooi lo000ooi lo000ooi lo000ooi

Zn - B

~ I ,O,0101~,fij~ o 10 20 40 80 ppm Z n

Fig. 8

Map of the Zn distribution in forest soils in the Belgian Kempen.

~ .. 0· .. ····· ........ .

... ~ f?\ h \. "" . .:;.! .... /" ... ".r:!f .fr:h '~;i' ~" ....... .:~/ 0, '~ .. .. .. ' ~ . """" .. ~ ®'~"~\.,, f?:A ~_ cQ0t'0~~~ .... ·\®"t0

0 0 ®

00 00 ~0@DO

\ ( . J?) ro AD~~ PKAW N"l (6) 0 \r "'WERPEN ~ cS 0 0 ~"OJ 0 ~.~ "Q!J °

~

\ · ~ 0 0000 ~/~ ~0~O OY///~ UER 0~~ r! 00 0~

",,®,~~'\~®fiJJ 0 0 ° ';" ° ",)' "".' /} ,,/""';0' gRSC': D~,,~~ 0 0 ®. ® 0 0 ~"", .... ' \')/'- A \" 'ASSE" ° ° 0~" Cd-B .. i ®~@ 'J ~ I p,01 o~ ,Lom-Cd

v.> 0 0.15 0,3 ,

Fig. 9

Map of the Cd distribution in forest soils in the Belgian Kempen.

0·' 0· .. ····· .~ ...... .

A ~ .. ·®0 /~\ ................ Y ('riJ 0,,\,.,.;,&, .-;(. _ .I "" 0 , ......... ~0 ...... .. 0 ... 0 e?J

O ~

-""~"0~ 0 0

~® 0 ®0 ®®~O

.]). L. ~; AN; WERPEN rI ~ 00~2 0 ~_~

, • ~ 'Ul 0 ~'Ul " •• , LIER . ~ 0~~~0

~ '0" 0 . 10\O'~/ .ES "·, .. 1'-...... ,.) .... "./.",,, . .1 .:.,,,"' ,

Pb - B

~ 2 4 6 8 10 Km 20 ................ """' ....

~ I 1010 1~1~le ~

I I I I 20 40 80 1&0 ppm Pb

Fig. 10

Map of the Pb distribution in forest soils in the Belgian Kempen.

- --

0······ .. C) : .... ~ ... ~3y ................... ~/ ·0'/.' ~0) \\

1"·0 ~ : t7?\: .·0: A : ............. ~ t7/\ ~".::::~'" ! 0 2 4 6 8 10 Km 20

~ .. 0 0 ~ 'G:1 , ..... ~\ .... f?l n./ I ............. ..........

..... \ .122 00 ~00000

000

00

0 0 0 0

• AN;W,"," , ~ iE~SEN ~ - ;ro.~!~~;iiJ~······® .. :::'>

U~R ~ ~ 0000 01i~ 0 000~S 0 ~. A;i:; o ~0 J2 '~ 0~0 l@{' .~.O, .. 00 0 ! , . ,. 0 ' 0 0 " O;F3J 0 0 ;

,·_·7./z\ ..... ~ .... \ c· ... __ ... _ ...... -... [······~·,·, "'IO -(2"" · ~O 00 0 0 0 0 ,:'/ './ • DIESV GENK" •

Cu - B AA RSC NOT ( • 0 ·0 0 0 ';.>' ~ I 000~@ "/'j ",ssm 0 0 n-.0;"· Ol I I I I I ! '<:.d ._.i

o 3 6 12 24 ppm Cu [ •• ) ;'

Fig. 11

Map of the Cu distribution in forest soils in the Belgian Kempen.

2 4 6 8 10 Km 20

Iwwi ...... - .......... ~

Zn - A

N 000~" ~ I1 I I I I .... 10 20 40 80 ppm Zn

Fig. 12

Map of the Zn distribution in field or grassland soils in the Belgian Kempen.

0··· .... ··\ .......... ~ .:/ ~ ,.... '<4 ~ '<:.R t7/\

....... ~ • ! ·0 f?\ ~ \G::' .,'0 '. ®"\ ~ l ............. ~j ® ~.~~:.. . ,,/ .I 0 2 4 6 8 10 Km 20

~. ~ ...... .... ::. .\ RV... ~.... I ""'" ...... ..... ..... ... ..... ® ~ _ ·u.,-r)a ( \ .

..... \. ® ®O '0~~0® ®

®0~~ 0 ~ ~~ ®

~

AN;WEoeEN re ~ lI~R ® 0 _

~~~ '<:::.P. .... ~ ~ r .. ·· ~ / ' ... . ®~0 'u2. ,/.,) .r.~\_.,®'-"'\.~~\~ ®

\ ..... _ ......... r·,·._······_·~.i: 0 t7À • ~O 00 0 '.' V. OIES~ Cd - A AARSCHOT /)

000~~ < NI "\,/"" ~ I : '-l I I I I - i

~ alS a3 0.6 t2 ppm Cd :...)

Fig. 13

Map of the cd distribution in field or grassland soils in the Belgian Kempen,

2 I. 6 8 10 Km 20 ....., ....., ....., ....., ....., i

Pb -A

~ 00®~@ 00 I1 1 1 I I *+

10 20 1.0 80 ppm Pb

Fig. 14

Map of the Pb distribution in field or grassland soils in the Belgian Kempen.

-- -

~

Cu-A

~ 11 10101~1€!Jj ... 16 ppm Cu

Fig. 15

Map of the Cu distribution in field or grassland soils in the Belgian Kempen.

We may now consider the soil surfaces for which the metal content exceeds more than four times the mean observed in the reference area (the region around Kalmthout) as being severely polluted. In the case of anormal distribution this limit should represent the rnean of the normal content to which is added six times the standard deviation, observed in this nearly unpolluted area and being about 50 % of the mean. In this way we regard as severely polluted the soil surfaces corresponding to 1/8 th of the standard sheet (named a sheet further on) where a mean metal content was found higher than

40 ppm Zn 1.2 ppm cd 120 ppm Pb 12 ppm Cu On account of this accepted standard we Eind for about 50 sheets: 13 with severe Zn pollution, 5 with severe cd pollution, 5 with

severe Pb pollution and 12 with severe Cu pollution. Three sheets: Mol (17/2), Lommel (17/3) and Overpelt (17/4)

show severe pollution for the four elements. Two sheets: Turnhout (8/8) and Opoeteren (26/2) show severe

pollution for Cu and Zn. Two sheets: Veldhoven (18/2) and Tessenderlo (25/1) show severe

pollution for Zn and cd. There are seven sheets with strong pollution for Cu only : Wortel (8/3), Beerse (8/7), Arendonk (9/5); Lille (16/3), Kasterlee

(16/4), Retie (17/1) and Geel (16/8). There are also six sheets showing severe pollution for Zn alone; Hamont (18/1), Meeuwen (18/5), Bree (18/6), Maaseik (18/7), Leo­

poldsburg (17/7) and Peer (17/8). We notice here clearly how the East of the Province of Antwerp

stands out with respect to Cu pollution and the North of the Province of Limburg to Zn, Cd and Pb pollution.

To answer the question whether "these general metal concentrations in the soil surface may he harmful to agriculture or to the wild nature, we must consult other investigators. We have also to take into account that we have determined the total content and not the available metal contents and that the absorption by the plant will depend upon e.g. the pH of the soil solution and that not all plants react in the same way.

Following Henckens (1975) Cu would be harmful to plant growing at soil concentrations ranging from 50 to 75 ppm and upwards, and Zn from 250 to 300 ppm. Pb would only lower the yield öf some plants with metal contents above 1,000 ppm. For Cd no limiting values are given. Ph and Cd when ahsorhed in the plant tissues even without harm to them, may intoxicate cattle and humans. Altough general

220

metal contents have not reached these harmfullimits over large sur­faces, caution is indicated locally and prevention is better than cure.

We thank Drs. P. Darius and Dr. W. Mortier for their advice and help, with the statistical approach and the computer calculations respectively and Prof G. King for checking the English text.

We thank the 'Nationaal Fonds voor Wetenschappelijk Onderzoek' which supported this work hy providing funds to purchase an A tomic Spectroscopy apparatus.

REFERENCES

Buchauer M. J., (1973). Con tamination of Soil and Vegetation near a Zinc Smelter by Zinc, Cadmium, Copper and Lead. Environmental Science & Technology Vol. 7, p. 131-135.

Cottenie A., Verloo M., Kiekens L., Velghe G., (1976). Analysemethoden voor planten en gronden. R.U.G. Fak. Landbouwwetenschappen Gent, 56 p.

De Venter J., (Bodemkundige dienst van België), (1977). Personal communication.

Henckens C. H., (1975). Zuiveringsslib in de landbouw. Bedrijfsontwikkeling, Vol. 6, p. 98-103.

Katalymov M. W., (1969). Mikroährstoffe, Mikronährstoffdüngung. VEB Deutscher Landwirtschaftsverlag, Berlin, 280 p.

Lagerwerff J. V., Brower D. L. & BiersdorfG. T., (1973). Accumulation of Cadmium, Copper, Lead and Zinc in Soil and Vegetarion in the Proximity of a Smelter. Proc. 6th Am. Conf on Trace Substances in Environmental Health, Univ. Missouri, p. 71. .

SchnitzerM. & DesjardinsJ. G., (1962). Molecular and Equivalent Weights of the Organic Matter of a Podzol. Soil Science Society Proceedings, Vol. 26, p. 362-365.

Stevenson F. J., (1977). Nature of Divalent Transition Metal Complexes as Revealed hy a Modified Potentio­metric Titration Method. Soil Science, Vol. 123, p. 10-17.

Vanherwegen P., (1977). Fixatie en mobiliteit van zware metalen in de bodem; Eindwerk Fak. Landbouwwetenschappen K. U. Leuven, Leuven.

221

Vanherwegen P., (1977 2) Unpublished Results.

Yasudo M., Yamasaki K. & Ohtaki H., (1960). Stability of Complexes of Several Carboxylic Acids F onned with Bivalen t Metals. Bull. Chem. Soc. Japan, Vol. 33, p. 1067-1070.

Summary

The Belgian Kempen (about 4 000 km2 in N. E. Belgium) is the site of many nonferrous metallurgy plants for more than a century.

224 surface samples of forest soils and 214 surface samples of cultivated soils were taken mostly in pairs from the same locality. The metals Zn, Cd, Pb and Cu in the samples were detennined by atomie absorption spectroscopy af ter extrac­rion with 0.5 N HN03. Research indieated a relative standard deviation in the contents of about 50 % for sampling at distances of 4 km and 200 m and of about 30 % for distances of 20 mand 2 m. Referring to the mean metal contents of the least polluted area (around Kalmthout), nonnal contents for forest soils (to a depth of 6 cm) could be defined as :

5-15 ppm Zn; 0.15-0.45 ppm Cd; 15-45 ppm Pb; 1.5-4.5 ppm Cu. For the whole Kempen area however, a log-nonnal distribution in the metal contents was found, indicating strong pollu rion gradients. In undisturbed forest soils one fmds mean contents of twice as much Pb and 1.5 times more Cu than in cultivated soils, but about the same contents of Zn and cd. Recent dispersal of Pb fr om the air originating from the combustion of anti-knock gasolines may be a possible factor in lead accumulation. In the East of the Province of Antwerp (960 km2) the mean Cu content is at least four times higher than normal and in the North of the Province of Limburg there are may areas with more than four times the nonnal contents of Zn, Cd and Pb, indieating a speciflc pollution fr om nonferrous metallurgy plants in these areas. The weak correlation between the copper and zinc contents compared to the stronger cotrelations of the lead and especially cadmium contents with those of zinc may be explained in the same way.

De verspreiding van zware metalen over de Kempische bodem

Samenvatting

In de Belgische Kempen (ongeveer 4.000 km2 in N.O. België) waar vele non­ferrometaalbedrijven al een lange aktiviteit kennen, werden 224 bosbodems en 214 akker- of weidebodems, meestal in paren per plaats bemonsterd (tot 6 cm diepte). Door atoom-absorptie spektroskopie werden Zn, Cd, Pb en Cu erin be­paald na extractie met 0.5 N HN03. Onderzoek toont aan dat de relatieve stan­daardafwijking der gehalten voor staalname op 4 km en 200 m afstand rond de 50 % ligt en voor 20 m en 2 m afstand nog 30 % blijft bedragen. Voortgaande op de gemiddelde gehalten in het minst bezoedelde gebied (rond Kalmthout) worden voor bosbodems tot 6 cm diepte als normale gehalten gevonden:

5-15 ppm Zn; 0.15-0,45 ppm Cd; 15-45 ppm Pbj 1,5-4,5 ppm Cu. Voor heel

222

de Kempen wordt echter een log-nonnale verdeling der gehalten gevonden, wat op sterke bezoedelingsgradienten zou wijzen. In onberoerde bosbodems vindt men gemiddeld 2 maal meer lood en 1,5 maal meer Koper dan in akker- of weide­bodems, maar ongeveer evenveel Zink en Cadmium. Recente Lood-verspreiding vanuit de lucht afkomstig van verbranding van klopwerende benzines zou daar voor Lood niet vreemd aan zijn. In het Oosten der Provincie Antwerpen (960 km2) blijkt het gemiddeld Koper-gehalte minstens 4 maal hoger te zijn dan nonnaal, en in het Noorden der Provincie Limburg zijn eveneens veel gebieden met meer dan 4 maal hogere gehalten in Zink, Cadmium en Lood, wat aan een specifieke be­zoedeling vanuit de non-ferrometaalindustrie in die streken kan toegeschreven worden. In dezelfde zin zijn de zwakke correlatie tussen Koper en Zinkgehalten uit te leggen vergeleken met de sterkere correlatie van Lood en vooral Cadmium­gehalten met die van Zink.

La répartition de métaux lourds dans les sols de la Campine

Résumé

La Campine BeIge (environ 4 000 km 2 dans Ie N. E. de la Belgique) connait depuis déjà longtemps une forte activité d'industries des métaux non ferreux. No,:!s y avons receuilli 224 échantillons dans des sols forestiers et 214 échantillons dans des sols cultivés Uusqu'à 6 cm de profondeur) pour la plupart en paires de la même localité. Les éléments Zn, Cd, Pb et Cu ont été détenninés par absorption atomique, après extraction avec HN03 0,5 N. L'écart type des teneurs pour ce qui concerne l'échantillonage à des distances de 4 km et de 200 m s'élève à 50 % et pour des distances de 20 m et de 2 m il reste encore 30 %. Se référant aux moyennes de la région la moins polluée (aux alentours de Kahnthout) les teneurs nonnales pour les sols forestiers jusqu'à 6 cm de profondeur sont :

5-15 ppm Zn; 0,15-045 ppm Cd; 15-45 ppm Pb; 1-5-4,5 ppm Cu. Pour toute la Campine on trouve néanmoins une répartition log nonnale des teneurs , ce qui indiquerait des forts gradients de pollution. Dans les sols forestiers non remués on trouve en moyenne 2 fois plus de Pb et 1,5 fois plus de Cu que dans les sols cultivés, mais environ la même quantité de Zn et de Cd. Pour ce ,qui concerne Ie Pb la récente dissipation de Pb par les essences antidétonnants n'y sera pas etran­gère. Dans l'Est de la Province d'Anvers (960 km2) la moyenne en Cu est au moins 4 fois plus haute et dans Ie Nord de la Province de timbourg les teneurs moyennes en Zn, cd et Pb sont à beaucoup d'endroits aussi 4 fois plus grands que la moyenne nonnale. La cause de cette pollution differente peut être cherché dans l'implantation d'industries des métaux non ferreux specifiques. La faible corrélation entte les teneurs de Cu et de Zn par rapport à la plus forte corrélation des teneurs de Pb et surtout de cd avec ceIle de Zn peut s'expliquer de la même façon.

223

PEDOLOGIE, XXX, 2, p. 225-241,3 fig., 1 tab. Gand, 1980.

ESSAI DE CLASSIFICATION PRATIQUE DES HUMUS

F. DELECOUR

1.INTRODUCTION

Dans une publication antérieure (Delecour, 1978), nous avons rappelé qu'un des objectifs de nos recherches est de fournir au forestier un outil susceptible de l'aider à résoudre ses problèmes d'aménage:­ment. A cette même occasion, nous avions mis en évidence, pour la hêtraie ardennaise, un certain nombre de caractéristiques édaphiques liées à la production forestière. Parmi ces caractéristiques, la plus intéressante est, sans conteste, la forme d'humus.

Dès lors, il s'imposait de poursuivre notre étude en présentant, en guise de base de travail, un système de classification pratique des humus, assorti d'une clé de détermination utilisable sur Ie terrain. Celle-ci est basée sur l'examen macro-morphologique des horizons holo- et hémiorganiques, ainsi que, éventuellement, sur la déterinina­tion de quelques unes de leurs caractéristiques fondamentales, comme l'acidité et la présence de carbonates.

D'un point de vue pratique, il eut été suffisant de prévoir la déter­mination des humus forestiers. Toutefois, dans la perspective d'une utilisation forestière éventuelle d'autres formations végétales (landes, prairies, ... ), il était intéressant d'élargir nos préoccupations jusqu'aux humus caractéristiques de ces formations.

Cette classification et cette clé de détermination résultent, à la fois, de multiples observations, principalement en hêtraie, et de compila­tions bibliographiques.

Communication présentée à la tribune de la Société Beige de Pédologie, Ie 16 janvier 1980.

F. Delecour - Centre de Recherche et de Promotion F orestières - Section PedoJogie (I.R.S.I.A.), Dir. Prof. G. Hanotiaux - Service Science du Sol- Faculté des Sciences Agronomiques de l'Etat, Gembloux, BeIgique.

225

2. BASES DE LA CLASSIFICATION DES FORMES D'HUMUS

2.1. NOTION DE FORME D'HUMUS

L'expression "forme d'humus" a été définie par Müller (1887). Elle désigne des formations naturelles, biologiquement actives, développées en surface du sol, au départ de débris végétaux et animaux à tous les stades de décomposition et différenciées en horizons organiques et/ou organo-minéraux. L'ensemble de ceux-ci constitue Ie proft.l humique.

2.2. SYSTÈMES DE CLASSIFICATION DES HUMUS

On trouve, dans la littérature, de nom breux systèmes de classift.ca­tion des formes d'humus. Citons, entre autres, les ouvrages de Bernier (1975), Bonneau et Souchier (1979), Duchaufour (1977), Ehwald (1958), Hartmann (1944,1951), Kubiena(1953) , Lafond (1952), Wilde (1954, 1966). Pour les végétations herbacées, ajoutons-y la clas­sification de Barratt (1964 ).

Notre propos n'est pas de comparer, de discuter des mérites de ces divers systèmes qui, d'ailleurs, ne sont pas toujours comparables. Cer­taines de ces classift.cations sont dites "ecologique", "biochimique" (par exemple, Duchaufour, 1977), etc ... D'une manière générale, elles peuvent être qualift.ées de "fonctionnelles" car elles son t basées sur les divers processus d'humift.cation. Elles font fréquemment appel à des critères non directement décelables sur Ie terrain; caractéristiques micromorphologiques, rapport C/N, taux d'humification, etc ...

S'ils sont difft.cilement utilisables pratiquement, de tels systèmes sont d'une grande utilité pour la compréhension des phénomènes et des processus de l'humift.cation. C'est pourquoi les travaux de ce type doivent être poursuivis. A cet égard, on peut signaler les travaux de l'école nancéienne (Brun, 1978; Toutain, 1974, etc ... ) qui illustrent, notamment, l'importance des champignons supérieurs ("pourritures blanches"). Dans Ie même ordre d'idée, l'excellent ouvrage de Zacha­riae (1965) met en évidence Ie rale énorme de la pédofaune dans l'humification de la litière de hêtre.

2.3. NIVEAUX DE CLASSIFICATION

Le système présenté ici n'est pas "explicatif" mais "descriptif" et c'est bien pourquoi il est utilisable sur Ie terrain.

11 comporte sept niveaux de classification, répondant à des critères plus ou moins généraux ou particuliers. 11 s'agit, du haut vers Ie bas, de: - La CLASSE, correspondant aux conditions de subrnersion du sol.

226

Tableau 1

Classification des formes d'humus

CLASSE ORDRE SOUS-ORDRE FAMILLE FORME

Humus Humus brut submergé submergés

Tourbe submergée

Dy Vases Gyttja

Sapropèle

Anmoor IAnmoor oligotropli~

Humus ~nmoor mésotrophl

semi-terrestres T ourbe acide Tourbe T ourbe forestière

Tourbe neutre

Humus brut

Fibrimor Mor Mésimor

Humimor

Dysmoder (Eu) moder

Moder Moder mulleux Moder calcique

Humus Moder carbonaté

forestier Mull dystrophe Mull oligotrophe

Humus MuIl Mull mésotrophe

émergés Mull eutrophe Mull calcique

Humus Mull carbonaté

terrestres Mor granuleux Mor massif

Mor Mor feutré Mor feuilleté Mor rubané

Humus Mor mulleux

des végétations Mull-mor herbacees

MuIl grenu Mull massif

MuIl Mull fin Mull feutré Muil feuilleté Mullientiforme

227

- L'ORDRE, correspondant, pour les sols non submergés, aux condi­tions d'engorgement. - Le SOUS-ORDRE, caractérisé par la couverture végétale des sols non engorgés en permanence ou en sub-permanence. - La F AMILLE, correspondan t au degré de différenciation des hori­zons holorganiques et hémiorganiques et, notamment, à la présence d'horizons organiques diagnostiques (Of, Oh). - La FORME, répondan t à des critères divers, selon les unités définies par les niveaux supérieurs :

= Humus submergés : conditions locales de formation (nature des eaux) ;

= Humus semi-terrestres : acidité, origine des résidus végétaux; = Humus forestiers ; im portance relative des horizons holorganiques,

acidité, transition vers les horizons minéraux; = Humus des végétations herbacées : structure, épaisseur et arrange-

ment des horizons. - La PHASE, selon l'épaisseur du profil humique, correspondant à l'ensemble des horizons 0 ou H et A (voir les définitions ei-après). - Enfin, la VARIANTE, correspondant, pour les humus forestiers, au régime hydrique et, pour les muIl forestiers, à diverses caractéristiques de l'horizon Ah: structure, texture (Bernier, 1975) et couleur.

Les unités correspondant aux niveaux supérieurs, jusqu'à la forme, sont énumérées dans Ie tableau 1.

3. DEFINITION DES CRITERES DE DESCRIPTION

Nous l'avons déjà dit, la définition pratique des formes d'humus repose sur l'observation macro-morphologique des horizons organiques et humifères, ainsi que sur la détermination simp Ie de quelques unes de leurs caractéristiques. Pour éviter les équivoques, il est nécessaire que tous ces critères soient définis aussi clairement que possible.

3.1. DEFINITION DES HORIZONS ORGANIQUES ET HUMIFERES

La nomenclature des horizons holorganiques et hémiorganiques est basée, d'une part, sur Ie système proposé, dès 1967, par l'Association Internationale de Seience du Sol (A.I.S.S., 1967) et adopté par les services compétents de l'Organisation des Nations Unies pour l'Ali­mentation et l'Agriculture (F.A.O., 1977), d'autre part, sur les défini­tions et descriptions d'horizons organiques par Babel (1971). Ce sys­tème de nomenclature a aussi été adopté pour Ie Réseau International de Traitement des Données de Sols (A.C.C.T., 1978).

Les horizons répondent aux définitions ei-dessous (cf fig. 1).

228

BABEL. R.I.T.D.S.

Ln 011 L Ol

Lv 012 Fr Ofl

F Fm Of2

Of

Hr Ohl

H Oh Hf Oh2

Ahh

Ah Ah

Ahu

Fig. 1

Définition des horizons organiques et humiÎeres.

3.1.1. Horizons holorganiques non tourbeux, 0

Couche organique formée principalement à partir de Jeuilles, fleurs, ramilies, matérielligneux, ... , ordinairement non saturée par l'eau,sauf pendant de courtes périodes ne dépassant pas quelques jours.

Suivant l'état de décomposition des débris végétaux, affectant la morphologie d'ensemble de cet horizon, on peut distinguer divers sous­horizons: Ol (L de Hesselman, 1926) : Débris végétaux, éventuellement en mé­lange avec des quantités insiginifiantes de substances humifiées, princi­palement des déjections animales (moins de 10 % en volume). 11 peut se subdiviser lui-même en : 011 (Ln de Babel, 1971) : débris végétaux apparement non modifiés par rapport à leur état au moment de leur chute. 012 (Lv de Babel) . débris végétaux, plus ou moins fragmentés, visible-

229

ment modifiés depuis Ie moment de leur chute (couleur, cohésion, dureté, ... ). of (F de Hesselman) : Résidus végétaux, plus ou moins fragmentés, en mélange avec des proportions faibles à moyennes de substances humi­fiées, sous forme de déjections animales plus ou moins remaniées (10 à 70 % en volume). On peut subdiviser ce sous-horizon en : Of1 (Fr de Babel) : résidus végétaux nettement prédominants, avec faibles proportions de substances humifiées (10 à 30 % en volume). Of2 (Fm de Babel) : résidus végétaux, généralement fortement frag­mentés, mélangés à 30 à 70 % en volume de substances humifiées. Oh (H. de Hesselman) : substances humifiées fines (plus de 70 % en volume), avec des proportions faibles à nulles de résidus végétaux for­tement fragmentés : Oh1 (Hr de Babel) : 70 à 90 % en volume de substances humifiées, en mélange avec des résidus végétaux fortement fragmentés mais se re­connaissant sans peine comme tels. Oh2 (Hf de Babel) : plus de 90 % en volume de substances humifiées, avec des proportions très faibles à nulles de résidus végétaux très forte­ment fragmentés et peu identifiables dans la masse fralche.

3.1.2. Horizons holorganiques tourbeux, H (histo- = tissu)

Couche organique formée principalement à partir de mousses, joncs, laiches, roseaux, matérielligneux (aunes, notemment), ... et sa­turée par l'eau pendant des périodes prolongées.

L'état de décomposition des débris végétaux peut s'apprécier selon l'échelle de von Post (cf, par exemple, Delecour et Kindermans, 1977), comportant dix classes, basées sur: . - I 'identification possible des résidus végétaux, - Ie comportement de l'échantillon sous compression manuelle (cou-leur et turbidité de la solution exprimée).

Par analogie avec les horizons 0, nous admettons I 'utilisation des suffixes 1, f et h, avec les correspondances suivantes ; Hl : couche fibreuse non ou peu décomposée (fibrist) : von Post 1 à 3, Hf : couche moyennement décomposée (hémist) : von Post 4 à 7, Hh : décomposition (quasi-)complète (saprist) : von Post 8 à 10.

3.1.3. Horizons hérniorganiques, Ah

Horizon minéral superficiel nettement coloré par les composés hu­miques. Ah1 : partie supérieure du Ah, fortement à très fortement colorée par l'humus et de consistance meuble;

230

Ah2 : partie inférieure du Ah, moyennement à faiblement colorée par l'humus et de consistance moyennement meuble à massive. OAh : horizon de transition entre les horizons holorganiques 0 et l'horizon hémiorganique Ah et caractéristique des forrr..es moder et dysmoder. Très coloré (clarté 2 ou moins), Ie plus souvent à structure particulaire. 11 peut se distinguer du Ah par un toucher plus onctueux, dû à sa moins grande richesse en particules minérales, et du Oh par une tonalité généralement plus noiratre de sa couleur. Cet horizon corres­pond au Hi de Bernier (1975) ou au "H minéral" de Zachariae (1965).

3.2. TESTS PHYSICO-CHIMIQUES

3.2.1. Réaction

L'utilisation d'un pH-mètre colorimétrique de poche, genre Peha­meter Hellige à indicateur liquide ou Hellige-Truog à indicateur en poudre, suffit à classer Ie matériel dans une des classes suivantes d'aci­dité:

très acide acide neutre basique

pH< 5 5 ~ pH < 6 6~pH<7,5

pH ~ 7,5

3.2.2. Recherche des carbonates

11 s'agit du test classique de présence ou absence d'effervescence au contact d'acide chlorhydrique, HCl4N (1:3).

3.2.3. Epaisseur du profil humique

L'épaisseur du profil humique correspond, rappelons-Ie, à l'épais­seur de l'ensemble des horizons holorganiques et hémiQrganiques. Si l'on peut admettre les mêmes dénominations de catégories pour les diverses familIes d'humus, il est évident que les valeurs-seulls doivent être adaptées à chacun des cas particuliers. Par exemple, pour les tourbes, l'échelle sera Ie mètre, pour les humus forestiers, Ie déci­mètre.

Barratt (1964) a proposé des valeurs-seulls pour les humus des for­mations herbacées.

Pour les humus terrestres forestiers, nous reten ons les modalités suivantes :

très épais épais mince très mince

plus de 20 cm 10à20cm 5 à 10 cm moins de 5 cm

231

3.3. VARIANTES

Imitant Bernier (1975), nous admettons divers critères de variantes. Pour l'ensemble des humus forestiers, il s'agit des modalités du régime hydrique. Pour les mull forestiers, nous retenons la structure et la texture de l'horizon Ah, ainsi que sa couleur, particulièrement, les composantes darté (value) et intensité (chroma).

De notre point de vue, défini dès l'abord de la présente note, la signification pratique de ces variantes doit encore être précisée.

3.3.1. Régime hydrique

Cette variante trouve son utilité dans la précision des états extrêmes d'humidité ou de sécheresse. Elle est signalée par un des préfixes sui­vants:

hydro- : drainage général pauvre à très pauvre (gley ou pseudo-gley dans ou immédiatement sous l'horizon Ah),

(méso-) : drainage normal à modéré (habituellement non mention­né),

xéro : dimat subaride à aride; drainage excessif (dasse a de la carte des sols de Belgique).

3.3.2. Caractéristiques de l'horizon Ah

Pour les mull forestiers, ces divers critères serviront à attirer l'atten­tion sur des propriétés texturales extrêmes, ainsi que sur l'état de structuration. Les modalités chromatiques pourraient correspondre à des transitions vers les formes voisines (moder mulleux, par exemple). Texture argilo- : sym boles E et U de la carte des sols de Belgique, (limono-) : symboles A et L (habituellement non mentionné), sahlo- : sym holes P, S et Z.

Cet argument textural est parfois utilisé également par les pédolo­gues allemands (Babel, communication verbale). Structure grOSSIer : agrégats de plus de 5 mm, moyen : agrégats de 2 à 5 mm, fin : agrégats de moins de 2 mm, massif : absence de structure fragmentaire.

Cette dernière modalité recouvre, approximativement, Ie "post mull" de Jongerius & Schelling (1960). clarté clair : clarté supérieure à 3,

232

(normal) : clarté égale à 3, foncé : clarté inférieure à 3.

4. CLE DE DETERMINATION DES FORMES D'HUMUS

11 est à noter que l'on trouvera, dans cette clé, l'une ou l'autre for­me non mentionnée dans Ie tableau 1. Par exemple, les tangel, forme d'humus mixte, correspondant à un horizon holorganique 0 de type mor, reposant sur un horizon hérniorganique Ah de type muil (Kubiena, 1953 ).

D'autre part, la famûle muil-mor des formations herbacées ne figure pas dans la clé de détermination. Définis par Barratt (1964), ces mull­mor se caractérisent par un horizon Ah de complexation dont la richesse en matière organique Ie fait ressembler à un horizon Oh. Ils ne peuvent être distingués des mor qu'avec l'aide du microscope. Présents seulemen t sur certains soils squelettiques de type AC, ces mull-mor sont de très peu d'intérêt pour Ie forestier.

Les fig. 2 et 3 donnent une représentation schématique de quelques humus terrestres forestiers.

1 . Régime de submersion permanente (Humus sub­mergés, cf Kubiena, 1953)

la Pas de submersion ou submersion temporaire

2 Horizons organiques non macroscopiquement différenciés

2a Horizons organiques différenciés

3 Couche organique cohérente, d'aspect tourbeux 3a Couche organique meuble, d'aspect vaseux

4 Formation dans des eaux brunes; couche organique brune, constituée, presque exclusivement, de flocu­les humiques amorphes

4a Formation dans des eaux non colorées ou, excep­tionnellement, peu chargées en colloïdes humiques; couche organique grise ou gris-brun à noiratre

5 Odeur putride faible à nulle; humus riche en déjec­tions animales

Sa Odeur putride forte à nauséabonde; humus pauvre en déjections animales

6 Engorgement partiel ou total, permanent ou semi­permanent, par une nappe aquifère, perchée ou phréatique (Humus semi-terrestres)

6a Engorgement nul (régime de sécheresse relative ou de sécheresse) ou engorgement temporaire par une nappe perchée (Humus terrestres)

7 Couche organique (Ol) mince, plus ou moins dis-

2 6

h~mus brut subrnergé 3

~ tourbe neutre subrnergée 4

dy

5

gyttja

sapropèle

7

11

233

1----I

MULL

CALCIQUE

Fig. 2

Ol ~~~~ ~" ''::ó.O;'; ',.',~:,,~

0 ':

MULL MULL

DYSTROPHE

MODER MULLEUX

Représentation schématique de quelques humus terrestres forestiers.

continue; humus gris foncé à noir, riche en éléments minéraux, massif, boueux à l'état humide, terreux à l'état sec

7 a Couche holorganique plus ou moins épaisse, humus tourbeux, pauvre en matière minérale

8 Humus acide (pH < 5,5), relativement riche en rési­dus végétaux

8a Humus peu acide à neutre (pH> 5,5), pauvre à très pauvre en résidus végétaux

9 Tourbe très acide (pH < 5) constituée, essentielle­ment, à partir de sphaignes (tourbière haute, bog)

9a Tourbe peu acide à neutre, d'autre constitution

10 Tourbe constituée, essentiellement, à partir de débris de bois, fruits, feuilles et aiguilles d'arbres (surtout pins et bouleaux)

10a Tourbe fonnée en conditions de saturation penna,. nente par l'eau, constituée, essentiellement, à partir de roseaux, laiches ou mousses (Hypnacées) ou de débris de feuilles, bois et fniits d'aunes (tourbière basse, fen)

11 Formation forestière lla Formation herbacée (cf Barratt, 1964)

12 Présence d'une couche holorganique (litière) à la sur­face du sol

(anmoor) 8

(tourbes) 9

anmoor oligotrophe

anmoor mésotrophe

tourbe acide 10

tourbe forestière

tourbe neu tre

12 28

13

234

12a Absence ou quasi-absence de couche holorganique; seul un mince horizon Ol, plus ou moins discontinu, peut être présent (suivant Ie moment de l'année)

13 Couche holorganique non différenciée en horizons macroscopiquemen t décelables

13a Couche holorganique différenciée en horizons (Ol, Of, Oh)

14 Présence d'horizons Oh et/ou OAh 14a Absence d'horizonsOh et/ou OAh

15 Horizons holorganiques plus ou moins épais (> 10 cm), passant à un horizon Ah par une transition nette (absence de OAh)

15a Horizons holorganiques plus minces « 10 cm), passant progressivement à un horizon Ah de diffusion par l'intermédiaire d'un horizon OAh

16 Humus très acide, pauvre en déjections animales, sur­montant un Ah de diffusion généralement rr,ince

16a Humus riche en déjections imimales, surmontant un Ah de complexation, généralement épais; substrats calcareux dans l'étage subalpin .

17 . Horizons Of et Oh en proportions plus ou moins égales 17a Horizons Of et Oh en proportions différentes

18 Horizon Of nettement dominant 18a Horizon Oh nettement dominant

19 Horizons Of et Oh d'importance plus ou moins égale 19a Horizon Oh très mince, discontinu ou temporaire

20 Humus acide à très acide sur substrats siliceux pauvres en calcaire; horizon Ah à structure particulaire ou mas­sive

20a Humus neutre à faiblement alcalin sur substrats carbo-natés, pulvérulent à l'état sec

21 Non effervescent aux acides dans la matrice 21a Effervescent aux acides dans la matrice

22 Horizon Of comportant les deux sous-horizons OH et Of2; Ah de complexation, mince, noiratre (clarté Munsell < 3?)

22a Horizon oH seulement; Ah de complexation générale­ment mince (quelques cm), gris foncé, à structure géné­ralement grumeleuse fine; substrats siliceux acides

23 Horizon Ah présentant des traces de pseudo-gley (taches de rouille), à structure fragmentaire (grume­leuse, polyédrique)

23a Horizon Ah sans trace de pseudo-gley

24 Horizon Ah effervescent aux acides dans la matrice 24a Horizon Ah non effervescent dans la matrice

23

humus brut

14

15 22

16

19

(mor) 17

tangel

mésimor 18

fibrimor humimor

dysmoder 20

(eu) moder

21

. moder calcique moder carbonaté

moder mulleux

mull .dystrophe

hydromull 24

mull carbonaté 25

235

MODER DYSMODER FIBRIMOR HUMIMOR

Fig. 3

Représentation schématique de quelques humus terrestres forestiers.

25 Horizon Ah à pH ~ 7,5, à structure très nette 25a Horizon Ah à pH < 7,5

muil calcique 26

26 Horizon Ah à pH ~ 6 26a Horizon Ah à pH < 6

muIl eutrophe (ou neutre ) 27

27 Horizon Ah à pH ~ 5 27a Horizon Ah à pH < 5

. muil mésotrophe muil oligotrophe (ou acide)

28 Transition peu nette entre les horizons humi-fères et les horizons minéraux; horizon Ah de complexation

28a Transition nette à très nette entre les horizons humifères et les horizons minéraux; pas de Ah de complexation

29 Horizons Ol et Of absents ou très minces 29a Horizons 01 et/ou Of présents

30 Horizon Ah à structure grenue ou grumeleuse plus ou moins nette

30a Horizon Ah massif à structure polyédrique grossière; racines présentes seulement Ie long des faces de structure (massive mull)

31 Horizon Ah épais (> 15 cm); racines très ramifiées (strongly granular muil)

31a Horizon Ah peu épais « 15 cm); racines peu ram i­fiées, concentrées sous la surface (weakly granular mull)

32 Horizons 01 et/ou Of minces « 2 cm) 32a Horizons Ol et/ou Of épais (2-5 cm ou plus); sur sols

plus ou moins sque1ettiques

(mull) 29

(mor) 35

30 32

31

mull massif

muil grenu épais

muil grenu miitce

33

34

236

33 Horizon Ah à structure grenue devenant plus grossière vers Ie bas; sans intercalation de résidus végétaux (fme mull)

33a Horizon Ah de même structure mais avec intercala­tion de résidus végétaux; prédominance de racines mortes, très abondantes sous la surface (matted muIl)

34 Horizons OL et Of épais, feuilletés (laminated mull) 34a Horizon ol mince; dérangement de la superposi­

tion naturelle des horizons : résidus végétaux inter­stratifiés (lenticular muIl)

35 Horizons Ol et Of absents ou très minces; sur sols · squelettiques très minces, riches en matières orga­niques (Proto-rendzines et Proto-rankers selon Kubiena)

35a Horizons Ol et Of épais

36 Horizon Oh épais, à structure grumeleuse, très forte à l'état sec; racines très ramifiées (granular mor)

36a Horizon Oh massif à l'état frais ou humide, pulvé­rulent à l' état sec

37 . Horizons ol et Of tninces; racines peu ramifiées (massive mor)

37a Horizon Ol et Of absents; racines mortes très abon­dantes (matted mor)

38 Superposition normale des horizons Ol, Of, Oh; 01 et Of feuilletés, Oh massif (laminated mor)

38a Superposition anormale des horizons ol, Of et Oh

39 Superposition de plusieurs séquences of~h (banded mor)

39a Présence d'un mince horizon Ah de diffusion (mullized mor)

5. EN GUISE DE CONCLUSION

mull fin

mull feutré

mull feuilleté

mulllentiforme

36 38

mor granuleux

37

mor massif

mor feutré

mor feuilleté 39

mor rubané

mor mulleux

Comme point de départ de la poursuite du travail sur la caractérisa­tion des stations forestières, nous avons présenté, dans les pages précé­dentes, un essai de classification pratique des fonnes d'humus, assortie d'une clé de détermination. Celle-ci est basée sur un ensemble de ca­ractères observables ou aisément mesurables sur Ie terrain.

Nous I'avons dit dès Ie départ, ce système ne se veut pas définitif. 11 ne constitue qu 'une base de travail qui doit être soumise, sans cesse, à des tentatives d'amélioration. Idéalement:, d'un point de vue pratique, celles-ci devraient aller dans Ie sens ·d'une simplification, en vue de faciliter Ie travail du praticien utilisateur du sol.

11 est évident que, pour cela, notre attention se portera, principale-

237

ment, sur les humus forestiers, ainsi que sur ceux des milieux qui pour­raient, éventueilement, être mieux mis en valeur par une affectation forestière. Ainsi, nous pourrons, dès à présent, nous détourner des humus submergés. Ceux-ci sont, sans doute les plus mal connus des humus (Babel, 1975) et, d'autre part, ils occupent des sites qui ne seront que très exceptionneilement utilisés au boisement.

Pour la même raison, nous ne retiendrons que certaines formes d'hu­mus "herbacés". C'est ainsi que nous pourrons négliger les mor granu­leux, massif et feutré, ainsi que les muil feuilleté et lentiforme. D'après Barratt (1964), ces formes d'humus sont caractéristiques de sols squelettiques ou très superficiels (Lithosols), inintéressants pour Ie forestier.

Pour Ie reste, il s'agira d'étudier la signification pratique des niveaux inférieurs de classification (phase et variante, notamment) et de re­chercher des corrélations éventueiles entre les caractères observés. Par exemple, Ie muil dystrophe n'apparaîtra-t-il pas toujours de structure fine? Ie muil carbonaté n'est-il pas toujours foncé et grossier? sera-t­il nécessaire de maintenir la distinction entre muil dystrophe et muil oligotrophe, tous deux égalemen t très acides ? ne sera-t-il pas possible d'utiliser des critères similaires pour les humus forestiers et "herbacés"? etc ...

Cet objectif ne pourra être atteint que par la multiplication des ob­servations, en relation avec la productivité forestière. Dans cette opti­que, la coilaboration avec les praticiens et avec d'autres organismes de recherche ne pourra être que bénéfique.

Remerciements

Nous nous en voudrions de passer sous silence les encouragements . que ne cesse de nous manifester le professeur Hanotiaux, ainsi que les nombreuses et [ructueuses discussions que nous avons eues et que nous continuons à avoir avec nos collègues et amis U. Babel (Stuttgart), F. Toutain (Nancy), H. Van Praag et F. Weissen.

Nos remerciements s'adressent également à l'IRSIA dont l'interven­tion financière nous permet de réaliser ce travail.

BIBLIOGRAPHIE

A.C.C.T., (1978). N onnalisation et Echange des Données Pédologiques par Ordinateur. Agence de Coopération CulturelIe et Technique, Paris, 192 p.

A.I.S.S., (1978). Groupe de travail sur la nomenclature des horizons du sol. Bulletin A.I.S.S., n° 31, 7-10. .

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Babel U., (1971). Gliederung und Beschreibung des Humusproflls in mitteleuropäischen Wäldem. Geodenna, 5, 297-324.

Babel U., (1975). Micromorphology of Soil Organic Matter. in GIESEKING J. E., ed. Soil Components. vol. 1, Organic Components, 369-473.

Barrat B. C., (1964). A classification of humus forms and micro-fabrics of temperate grasslands. J. Soil Sci., 15 (2) 342-356.

Bernier B., (1975). Vue d'ensemble de la classification des humus forestiers. in Manuel de Description des Sols sur Ie Terrain. Revisic.n 1978. Système d'Informatique des Sols Canadien, 3.1-3.17.

Bonneau M. & Souchier B., (1979). Pédologie. 2. Constituants et Propriétés des Sols. Masson, éd., Paris, 459 p.

Brun].]., (1978). Etude de quelques humus forestiers aérés acides de l'Est de la France. Thèse Univ. Nancy 1, 118 p. + annexes.

Delecour F., (1978). Facteurs édaphiques et productivité forestière. Péd'ologie, 28 (3), 271-284.

Delecour F. & Kindermans M., (1977). Manuel de Description des Sols. Service Sci. Sol, Fac. Agron. Gembloux, 111 p. + annexes.

Duchaufour Ph., (1977). Pédologie. 1. Pédogenèse et Classification. Masson, éd., Paris, 477 p.

Ehwald E., (1958). Die Einteilting der Waldhumusformen. Forst. Stand. Landwirt. BMBH, Hiltrup hei Münster, 23-30.

F.A.O., (1977). Guidelines for the Coding ofSoil Data (first draft). Manuscrit ronéotypé, 191 p.

Hartmann F., (1944). W aldhum usformen. Z. ges. Forstwes., 70,39-70.

Hartmann F., (1951). Der waldboden. Humus-, Boden- und Wurzeltypen als Standortsanzeiger. Österr. Productivitäts- Zentrum, Wien, 152 p.

Hessehnan H., (1926). Studies över harrskogen humusstäcke, dess egenskaper och beroende av skogsvar­den. Medd. Stat. Skogsförsöksanst., 22, 169-552.

]ongerius A. & Schelling ]., (1960). Micromorphology of organic matter formed under the influence of soil organisms especially soil fauna.

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Trans. 7th Int. Congr. Soil Sci., Madison (Wisc.) 2, 702-710.

Kubiena W., (1953). The Soils of Europe. Thomas Murby and Co, London, 318 p.

Lafond A., (1952). La Conservation de l'humus. Compt. Rend. Ass. Can. de Conservation, 23-30.

Müller P. E., (1887). Studien über die naturlichen Humusfonnen und deren Einwirkung aufVegetation und Boden. Springer, Berlin, 324 p.

Toutain F., (1974). Etude écologique de l'humification dans les hêtraies acidiphiles. Thèse Doct. Etat, Univ. Nancy 1, 114 p.

Wilde S. A., (1954). F orest humus: its genetic classification. Wisc. Acad. Sci. Arts and Letters, 43, 137-163.

Wilde S. A., (1966). A new systematic tenninology of forest humus layers. Soil Sci., 101,403-407.

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Résumé

L'auteur présente un système de classification des humus, basé sur un ensem­ble de caractères morphoIogiques observables sur Ie terrain. Les critères descrip­tifs sont définis; ils pennettent I'éIaboration d'une clé de détermination des for­mes d'humus submergés, semi-terrestres et terrestres.

Attempt for a practical classification of humus

Summary

The author presents a classification system of humus forms, based on a series of morphological features observabie in the field. The defined description criteria were used to prepare a detennination key of submerged, semi-terrestrial, and terrestrial humus forms.

Poging tot een praktische klassifikatie van humus

Samenvatting

De auteur stelt een klassifikatiesysteem voor gebaseerd op een reeks morfolo-

240

gische kenmerken, waarneembaar op het terrein. De beschrijvende kriteria worden bepaald; ze laten toe een sleutel op te stellen voor de karakterisatie van hydro­morfe, semi-hydromorfe en goed gedraineerde humusvormen.

241

PEDOLOGIE, XXX, 2, p. 243-273, 6 fig., 7 tab. Ghent, 1980.

PROPERTIES AND ORIGIN OF SEDIMENTS OF THE MEUSE RIVER IN THE NETHERLANDS AND BELGIUM

1. INTRODUCTION

J. M. M. VAN DEN BROEK H. W. VAN DER MAREL

The river Meuse has its origin on the plateau of Langres in France. The greater part of its sediment load which sequentially is deposited in delta area in the Netherlands, is obtained fr om the hilly regions of the Ardennes and Condroz from which many tributaries discharge in­to the Meuse.

It has been calculated that approximately 300.000 tons of dry matter is discharged yearly in the North Sea originating from the Meuse river system, Postma, (1957).

Since the late - Tertiary, the Meuse has contributed to the forma­tion of the large Rhine-Meuse delta of the Netherlands (Van den Broek & Van der Waals, 1967), the Meuse deposits forming the southern part of it. Pleistocene delta deposits consist of gravels, sands and loams. Only in the southern most part of the Netherlands they occur as a series of terrasses (Van den Broek & Maarleveld, 1963). Downstream they are covered by the younger deposits.

Sin ce the last part of the Subboreal c. 700 B. C. (Polak), the sedi­ments have become markedly finer of texture. In the central and western parts of the Netherlands, their thickness can be some metres. The holocene sediments are deposits in a meandering river system and occur as levee soils or back swamp soils depending on the physiographic position at the time of their deposition during winter and spring floods. Since the construction of dikes along the river, deposition of the recent sediments only occurs between these dikes.

In Belgium and France, alluvial deposits are less frequent and do not occur as a continuous strip alongside the river.

J. M. M. van den Broek - Soil scientist, International Institute for Aerial Survey and Earth Sciences (ITC), P. O. Box 6, Enschede, the Netherlands. (Formerly Soil Survey Institute, WagenIngen, the Netherlands). H. W. van der Marel- Soil Scientist, fonnerly Soil Survey Institute, Wageningen, the Netherlands and Laboratory of Soil Mechanics, Delft, the Netherlands.

243

Potassium fixation in certain alluvial soils in the Netherlands has been recognized in agricultural practises during the last decennia. The ability of the heavier textured soils to fix potassium strongly from applied potassium fertiliser had been observed for the first time in 1930 by H. Lindeman (at th at time Director of the Potassium Import Company) from the results ofhis K-fertilizer experiments.

Af ter Temme & Van der Marel (1952) and Van der Marel (1954) the K-fixation phenomenon would be caused by an expanded illite (14 .R) mineral in the day separate of these deposits. This day mineral contracts its layers when treated with a solution of KCI and it has swelling properties when treated with glycerol.

Strong K-fixation in these soils is not restricted to the top soil but is also found in the deeper layers. Apparently high K-fixation of the Meuse delta deposits in the Netherlands is not caused by strong weathering in situ or by K-exhaustion of the superficiallayers by crops. Sediments with high K-fixation fr om the hinterland of the Meuse river are likely to have heen deposited or are formed in the Meuse delta. An investigation of the nature of the source of rock sedi­ments in the hinterland from which the K-fixating deposits in the

. delta plain were derived, was, therefore, undertaken. See for localities of soil samples figure 1.

2. CATCHMENT AREA OF THE MEUSE RIVER AND lTS TRIBUTARIES

The catchment area of the Meuse indudes the Ardennes and Condroz regions in Belgium and Argonne and Ardennes regions in France (fig. 2).

By far the greater part of the material transported hy the Meuse and deposited in the delta area in the Netherlands, originates from rocks of the catchment area in Belgium.

The Ardennes peneplain with an altitude of 300-600 m above sea­level and with many important tributaries to the Meuse river consists of Cambrian and Lower Devonian sandstones and slates which are more or Ie ss schistosic. A shallow incoherent loess cover of Pleistocene age (where not eroded) is mixed with the weathered rocks in which soil profiles have been developed - Deckers, 1958, 1959a, 1959b. About 20-35 % of the area consists of schistosic sandstones and 30-50 % of slaty and schistosic rocks - Tavernier & Maréchal (1958).

The soil profiles which are formed on these rocks are shallow. They are of the Brown Podzolic and the Acid Brown Forest soil type, developed on a thin layer of weathered rock. Hanotiaux & Bourguignon

244

o SOkm

Fig. 1

~I------------------~I

o Brussels

BELGI UM

Phi lippeville o

Localities of samples investigated.

..

o 's -Hertogenbosch

o Hosselt

Maastricht t' "

O· Marche

St.Hubert o

.,.

245

o Brussels

'-_ _ _____ -'<SOkm

BELG/UM

... "' ........... ~.+""

.~?..---------"': .. --

o Brussels

p~e 0i'--_______ ....:;50km

_ sondstone, quortz ite, psommite

C=:J limestone , poloeozoicum

c=J schis ts . devonion

Fig. 2

" ---~ ... 0 Maastricht ," . .

" " 4;, oAochen .,f ..... .... ...,...o(..". ......... ~+-

~ ... \ ~ ~

~~} ....... "' .. lf

~ ' ..

I ;": ::: :.'J schists, psommite with cool , carbonion

c::::=J quortz ite, schists, eodevonion, cambrium

Geographic regions and the related geologïcal formations in the catchment area of the Meuse river in Belgium.

246

(1957) found ca 20-25 % illite and 12 % vermiculite in these soils. The Condroz region consits of WSW-ENE oriented alternating crests of Upper Devonian psammites and depressions of Lower Carbonian lime­stones. The elevations vary from 220 m to 300 m. By selective erosion af ter the Hercynian orogenesis the relatively harder psammite rocks have been left as the crests, the softer limestones forming the depres­sions. Pleistocene loess as a non coherent cover is mainly found in the depressions and on large plateaux (Maréchal 1956,1958,1961).

Psammitic rocks consist of sandstones intercalated with shallow lamines of schistlayers;locally they are developed as calcarous sand­stones or sandy limestones of neritic origin - van Straten (1954). Where not attacked by Quarternary erosion deep fossile soil profiles occur in psammitic rocks, dating from Tertiary or Early-Pleistocene age (Maréchal1958).

They are of the Lateritic and Red-Y ellow Podzolic soil type, in­dicating a genesis in warm tropical dimates with high rainfall. Potassium fixation is high and is caused by loss of K from mica (mainly musco­vite with only small amounts of biotite)which is the prevailing day mineral in the original rock.

In X-ray analyses maxima are observed at 7 .R (kaolinite) and 10 .R (mica) and in the case of i!J. situ weathered psammites a maximum at 14,68 J\ (expanded illite);- r..1aréchal (1958).

The limestones in the Condroz are covered by a shallow weatherin~ layer of red-brown day crust representing a Terra Rossa type of soil­Hallet (1957). This is a common characteristic for limestones which have small amounts of fine (day) substances. This Terra Rossa, which fixes potassium strongly, is considered a fossile soil resulting also from warm rainy dimates. The coarser material (> 16 J1) in these soils con­sists mainly of quartz. In the finer fractions « 16 J1) illite, inter­mediates, expanded illite and swelling illites have been found (Hallet 1957). Under the present dimate such a type of strong weathering action will not occur. The transition zone of Condroz and Ardennes is called Famenne region and consists predominantly of Upper Devonian shales. It is a large depression with a mean elevation of 200 m. In contrast with the Condroz region where fossile soils occur extensively, these are hardly found in the Famenne region as a consequence of in­tensive erosion in the Quarternary, Maréchal (1958). The soils are only shallow and comparable to those of the Ardennes. They are of the type Brown Podzolic Soil or Acid Brown Soil,Manil (1953), Deckers & Vanstallen (1955), Avril (1957), Pécrot & Avril (1954), Manil & Hanotiaux (1957), Deckers (1957), Henrard (1958).

247

3. METHODS OF ANAL YSIS

K-fixation It was determined af ter the wet and dry method i.e. 25 g of soil

was shaken or dried respectively with a KCI solution which contained 25 mg K20/100cc. The excess of KC1 was removed by 0.5 N Mg­acetate. The amount of K found at a separate Mg-acetate extraction of the soil was used to correct the amount of K fixed af ter the wet or dry method - for details Van der Marel (1954).

The above method is purely conventional as the amount of added KCI, the amount of soil, the reaction time and drying procedure are chosen arbitrarily.

Separation of the fractions 100 g. of soil was shaken for 2 hrs with NaOH to pH = c. 8 (P.P.)

and then sieved over a 80 mu sieve = separate> 80 mu. The other separates 16-80 mu, 2-16 mu and < 2 mu were obtained by sediment­ation in Atterberg cylinders with 0.01 N NaOH. The excess NaOH was washed out and the samples were dried at ca. 100oC.

Mineralogical analysis The> 80 mu samples were analysed by microscopy, the 16-80 mu,

2-16 mu and < 2 mu by X-ray spectroscopy. Contraction or swelling of the layers happened when the plates con­

tracted from 14 to 10 .R and fr om 14 to c. 17.8 R for samples treated with a concentrated solution of KCI or glycerol respectively. There is a considerable influence of the pretreatment of the sample on the shape of the (001) X-ray reflection(figure 3)-seealso Milne & Warshaw (1960).

The samples investigated here were air dried. For quantitative pur­poses the samples were first placed above 10 % H2S04 (relative humidity IV 93 hygroscopicity in an exsiccator for 7 days).

4. POTASSlUM FlXATION RELATED TO PARTICLE SIZE

In figure 4 the amounts of fixed potassium are plotted against the amount of separate < 16 mu. The data shows a low correlation, which was to be predicted on theoretical grounds.

Potassium fixation depends not only on the particle size but also on the kind of potassium fixing material. Vermiculite fixes K strongly because of the great interlayer charge, whereas montmorillonite fixes only small amounts. Expanded illite and swelling illite form. an inter­mediate position. There are no significant differences in K fixation be­tween the top and the subsoil or in the type of sediment. In table 1

248

air dry heated 120° C heated 120° C and afterwards 93 % R.H

heated 350°C and afterwards 93 % R.H

Alluvial - Netherlands 9,8

Kaollnlte ' 715 t\K'

H+ ~ NH+

1~ 4

Saturated wlth various cations

Fig. 3

Basal spacings of the day separate « 2 Jl) of some soil types. (A : loess, Nether­lands, B : al1uvial, Netherlands) as related to their pretreatment.

the results are indicated of K fixation in the separates > 80 Jl, 16-80 Jl

2-16 Jl and < 2 Jl, of soils from the Meuse river in the Netherlands. The figures show that the coarser particles with the exception of

those of weathered slates and shales, fix small amounts of potassium. Therefore the K fixation phenomenon is mainly attributed to the fin er particles of the soils.

In table 2 K fixation data is included of soils from the catchment area of the Meuse River and its tributaries in Belgium. K fixation of the separates < 2 Jl are high.

However in this case many separates > 80 Jl have also high K fixa­tion. This is caused by coarse mica of the weathered schists, shales and slates ..

249

------ WET------ !Q!' -1,-.--,-----,

80+-+---.+---. +'---+-+--1----; +--+R_'VE-t-R

"_UO-+S __

.. ~ " "

_~ ';::::5U:=:Br _ ,--____ --,

• ~ -, +, t--t--.--I-:;l.~.-t- --. .

'0 - +-rr-, ..r='~+---i

+: • -- r-. t---+--~---, ~-+--~+-~

I - : :-

80 . ." . ," -.: . .

' 0 -

r-, 1 1 -r-

i-- "UOS BïCKISH _ BELG lU "

I-- ! -. ..

-1 l-r--BIE S80SC H I

80 - r +

I ----+ ._-

t

40 - -........ .. ~. + .. -+.. .

ril --,---BIESBOSC"

• at

+ •• + + •••

+ •

o 1---4-1 _ - ---+----+----+~ o '0 80 '0 80 '0 80

Fig. 4

DRY ------TOP -I ·

! .' 1

RIVER MUOS

. . . ·

r--- "uos ' 8R ' CJ,SH_ -

.

. . . . . . I"

i

MUOS BAACKISH . BELGIUM

· . ' 0 80

<1 6 IJ

Wet (0 +) and dry (ll *) K-Hxation (%) of topsoils and sub-soils against the amount of separate < 16 J1 for several soil types from the Meuse delta.

In table 3 is K fixation data of the alluvium of the Meuse and its tributaries in Belgium. Also, in this case the separates < 2 J1 show high K fixation. Several soil separates> 80 J1 show an appreciable potassium Hxation. This in contrast to the separates in alluvial Meuse sediments in the Netherlands. The data shows no apparent difference between the soils of the Meuse and its tributaries, or between the top soils and the subsoils.

5. POTASSlUM FIXATION INCREASED BY LEACHING WITH SALTS

Potassium fixation can be increased by addition of various solutions. Rivière (1948) obtained a 14.ft illite mineral from the illitic (10.ft) day from Cormeilles by treatment with CaC12 or MgC12 solutions.

Caillère et al (1949 ) observed expansion of the lattice of phlogopite, muscovite and illite when treated with CaC12 or MgC12 solutions.

Wiklander (1950) observed enhanced K fixation by treating an illitic Clarende soil or ground biotite for 21 days with solutions of CaC12' MgC12 or NaC1 at 650 to 700 C.

250

No.

I. Sl S3 S8 2478 2479 2245 B58/59 912 439

II. 2247 2248 2249 2225 2202

111.

613 614 589 460 451 365 467 383 2448 369 2473 2476 1477

IV. 2481 598 622 309 313 379 304 329 305/308 L5 L8 B 52

Table 1

Potassium Hxation af ter the wet (W) and the dry (D) method in % for the original soil, and its separates > 80 Jl , 16-80 Jl, 2-16 Jl , < 2 Jl for samples along the Meuse river and its tributaries in the Netherlands.

Locality Depth <16~ Original > 80 Jl 16-80 Jl 2-16 Jl cm 'W D W D W D W D

Muds (river +, brackish x)

S. W. Netherlands Vrouwenpolder x 0-5 sand 29 45 ' 14 27 10 24 39 51 Wissekerke x 0-5 sand 30 49 25 37 6 21 27 46 Nw. Vosmeer x 0-5 sand 45 59 - - 9 29 12 33 O.Kil x 0-15 58 38 55 - - 4 36 34 51 W oensdrech t x 0-10 44 9 38 - - - - - -Nw. Merwede x 0-10 22 12 30 1 11 11 19 - -

Roosteren + 0-10 28 22 40 17 29 15 29 30 48 Hedel + 0-10 27 10 16 16 28 20 33 49 62 Ravenstein + 0-10 8 5 19 1 21 2 15 11 19

Bies bosch Amerplaat 40-60 28 31 9 30 9 23 - -

Amerplaat 80-100 31 34 54 4 30 7 30 - -

Amerplaat 130-140 24 21 40 2 23 1 30 18 49 ]annazand 20-40 66 85 93 - - 58 91 73 92 Bakkerskil 30-50 60 54 85 - - 40 76 52 85

Bommeierwaard, Land v. Altena Bergse Maas Hedrikhuizen 10-50 21 46 81 20 31 21 56 - -

Hedrikhuizen 50-90 18 47 85 18 29 35 50 - -

Ammerzoden 10-30 50 61 84 11 21 16 50 37 77 Kerkwijk 75-100 80 84 88 - - 40 79 92 98 Garneren 0-30 29 2 8 1 6 3 10 2 18 Delwijne 0-30 57 44 78 13 23 11 18 4 31 Bruchem 50-70 96 86 89 - - 81 95 94 98 Velddriel 0-30 81 67 88 - - 31 80 41 82 Velddriel 0-30 79 92 95 - - 58 86 86 97 Kerkdriel 0-30 20 5 21 13 23 11 18 4 31 Alem 5-40 89 70 90 - - - - 49 92 Alem 80-100 91 75 89 - - - - 53 84 Alem 100-120 82 69 89 - - - - 41 80

Limburg, Meuse and Waal Lith 0.25 87 68 90 - - - - 70 94 Born 230-250 50 64 84 - - 32 75 90 93 Heyen 40-60 39 42 78 5 17 13 29 - -

Wanssum 45-60 31 30 77 11 14 10 18 75 85 Wanssum 80-100 38 56 87 12 17 15 33 28 65 Heyen 120-140 16 49 79 16 27 - - - -Buggenum 5-20 34 47 82 - - 29 40 24 56 Buggenum 75-100 51 83 90 - - 34 63 66 86 Haelen 50-70 50 58 83 - - 20 40 26 74 Wessem 0-20 - 25 54 10 27 - - 40 49 Maasbracht 0-20 25 33 56 - - 23 52 31 66 Borgharen 40-65 39 58 86 - - 18 44 57 92

< 2 Jl W D

81 88 77 92 80 98 42 65 26 46 - -- -49 71 87 90

- -80 95 - -88 98 - -

- -- -- -- -

65 74 53 82 96 99 76 94 - -

53 79 76 96 81 99 80 96

95 96 88 99 - -81 92 - -

75 93 - -

- -- -

- -40 68 - -

I

3 17 21

I1A 67

I1B 25 26 64

lIlA 66 103 104 105

IIIB 61 123 129 125 127 128 129 130 131 75 76 78 79 155 153 157 102 106

IIIC 86

IIID 81

BIE 84 82

Table 2

Potassium flXation in original soil and its separates> 80 Jl, 16-80 Jl, 2-16 Jl and < 2 Jl for samples from the catchment area of the Meuse river and its tributaries in Belgium af ter the wet (W) and the dry (D) method (in %)

Locality Depth < o rigin al > 80 Jl 16-80 Jl 2-16Jl cm. 16Jl W D W D W D W D

Sandstone and slates more or less schistosic (Ardennes) Baraque Michel ± 45 38 15 22 21 25 6 14 48 71 Baraque Fraiture 65-90 36 14 20 - - 8 19 70 89 La Roche 0-30 28 20 40 - - 23 32 69 86

Shales,shallow weathered(Famenne) Nettine 0-20 31 29 52 78 90 29 46 35 84

Limestone, shallow weathered Marche-en -F amenne 0-15 66 73 85 - - - - 73 95 Han-s,-Lesse 0-15 42 68 86 - - 15 52 - -

Nettine 0-20 54 73 92 - - 33 60 44 98

Deeply weathered slates (Condroz) Fontenoy I 0-30 24 36 70 59 89 30 53 - -

Aywaille 0-20 30 33 57 65 80 22 47 2~ 77 Aywaille 20-70 28 34 56 58 78 18 45 35 67 Hodimont 0-10 28 23 41 65 82 31 46 70 84

Psammites, deeply weathered Fontenoy II 20-40 42 39 77 3 6 42 84 76 93 Nannine 4-10 30 30 53 - - 10 22 47 77 Nannine 20-30 31 34 61 37 69 16 30 - -Nannine 50-80 33 23 61 tr 19 8 19 - -

Nannine 140-160 15 8 19 14 18 1 10 - -Nannine 160-180 12 5 19 8 16 7 10 - -

Nannine ± 400 14 4 6 11 12 8 10 11 22 Evieux - 12 28 59 56 80 18 48 - -

Montfort - 34 17 26 48 68 12 22 18 36 Steuvere 40-70 51 71 93 42 84 - - 76 93 Steuvere 90-110 56 67 88 - - - - 30 80 Pesseaux 40-90 29 31 62 71 91 19 53 - -Pesseaux 90-120 23 43 69 38 84 - - - -

Ohey 50-80 63 32 43 - - 8 11 17 33 Ohey 100-110 51 24 51 - - 8 25 31 53 Ohey ± 200 13 21 39 45 60 26 35 49 60 Hotchamps 90-110 25 25 43 26 41 - - - -

Hoyemont 20-40 9 33 65 39 68 39 68 - -

Calcareous psammites, weathered Hody 20-40 76 92 97 - - - - - -

Calcareous shales, weathered Méan 0-30 59 85 96 - - - - - -

Calcareous sandstones, weathered Hody 20-40 79 70 85 - - - - - -Chardeneux 0-40 37 81 95 - - - - - -

252

<2Jl W D

92 98 90 95 50 62

73 98

86 94 90 96 92 95

79 95 75 81 81 92 74 94

- -

93 99 - -- -56 74 - -

66 78 - -

85 96 - -

92 96 - -- -

75 85 76 86 89 94 - -91 97

97 99

97 99

86 92 97 99

No.

49 51 135 46 48 119 113 132 133 134 140 33 145 148

13 42 151 39 160 161 162 163 165 167 168 169 170

Table 3

Potassium Hxation of original soil and its separates > 80 p, 16-80 p, 2-16 pand < 2 p for samples along the Meuse river and its tributaries in Belgium (in %)

Description Oepth < Original > 80p 16-80 P 2-16 P cm 16p W D W D W D W D

Meuse River Lanoy 0-20 21 18 32 24 40 13 34 60 81 Lanoy 50-80 51 70 92 - - 20 51 64 95 Annevoie 22-44 27 22 44 51 64 12 26 31 50 Hermall 0-20 31 24 37 - - 17 38 61 83 Hermall 85-100 28 71 92 20 46 26 48 - -

Ben Ahin 10-60 43 60 88 - - 18 54 82 96 Ben Ahin 90-125 - 57 89 - - 18 51 - -

Jambes 60-100 35 25 68 18 35 16 38 35 79 Jambes 30-90 34 14 51 19 38 4 18 16 43 Jambes 18-49 31 18 49 29 47 11 27 - -

Bloc Yvoir 11-50 27 45 70 - - 8 30 37 85 Hastière 30-50 40 56 85 - - 20 60 52 86 Waulsort 60-80 27 42 75 14 35 13 34 65 91 Heer 75-120 30 48 84 19 41 22 59 65 92

Tributaries Amblève, Trois-Ponts 50-100 36 14 35 19 28 . 4 15 17 39 Ourthe, Hamoir 0-10 38 32 70 40 65 8 35 55 91 Lesse, Anseremme 75-125 29 54 90 - - 13 28 76 95 Sambre, Han 20-40 38 55 62 - - 16 44 68 95 Sambre, Landelies I 0-20 25 28 56 31 51 - - 28 74 Sambre, Landelies I 30-50 21 24 62 31 66 11 35 - -

Sambre, Landelies I 60-80 29 38 69 29 48 9 29 24 66 Sambre, Landelies IJ 0-20 41 31 51 - - 9 20 65 79 Sambre, Landelies 11 50-65 47 40 68 - - 6 21 50 72 Sambre, Lobbes 0-20 35 34 58 33 44 6 23 41 77 Sambre, Lobbes . 25-45 33 35 77 - - 13 24 50 76 Sambre, Lobbes ' 50-70 27 26 64 - - 11 23 - -

Sambre, Lobbes 70-90 33 25 62 - - 7 22 32 61

Af ter the wet (W) and dry (D) method.

White (1951) used a 20 % Na, Co nitrate solution to open the

<2p W D

- -

92 98 80 92 - -

- -95 98 94 98 94 96 83 96 94 96 - -

80 94 - -- -

83 93 90 98 96 99 - -90 96 86 98 90 99 90 95 90 96 91 98 96 99 94 98 - -

layers of an illitic Pennsylvania soil. Hamdi (1959) used C02 saturated water during 8 motlths to change the original alluvial illitic sediment from the Ethiopian highlands into montmonillonite. In addition alkyl NH4 + ions may be interlayered between the layers of muscovite, biotite and illite resulting in a layer distance of 27-33 1\ (Weiss et al 1956 ).

253

N 111 ~

Table 4

Potassium Hxation af ter the wet and dry method (%), exehangeahle and in 0,1 n Hel soluhle K20 (0.001 %) and K20 dissolved hy sueeessive extraetions with 25 % Hel at 100 oe of soils whieh have heen exhausted hy 13 sueeesive plantings with oats. Dry matter of harvest in g. and K20 removed in mg for eaeh soil sample of 1 kg

Yields of oats Before the expèriment Af ter the experiment

Yields of oats -K20 in 25 % Hel Kj] ~:P K-fixation KzO KzO K-Hxa-No. Dry matter (g) K20 (mg) 0.001 % 0.1 ex- 0.1 exeh. tion

1-3 10-13 1-13 1-3 10-13 1-13 1 2 3 Total 0.001 eh. wet dry P.001 0.001 wet dry % 0.00 % % % % % %

%

Marine clays and muds 58 Lauwerszee 39,3 32,4 100,2 837 372 1980 90 34 20 144 52 16 8 20 6 3 11 31 219 Dollard 43,1 31,0 107,4 1519 369 2788 128 50 32 210 75 40 12 21 7 3 16 30 226 Beemster 47,5 42,0 129,2 1551 567 3229 128 46 26 200 36 27 3 35 8 2 25 48 228 Wieringermeer 43,5 35,8 115,8 893 440 2163 65 48 32 145 23 19 1 19 5 2 10 30 136 Goes 51,6 36,5 121,2 1505 543 3029 185 95 34 314 36 21 14 37 9 8 38 56 47 Tholen 42,2 28,6 102,2 1202 631 2752 108 62 38 208 24 21 26 48 8 7 28 53 156 Braakman 41,8 39,2 115,9 1418 496 2890 145 56 28 229 65 44 9 27 6 3 15 38

Riverclay 27 Wageningen 41,4 28,4 103,8 1196 541 2696 124 62 52 238 27 14 18 62 12 2 42 68 360 Hedel 43,7 40,4 119,4 1032 453 2387 104 30 28 162 21 12 6 38 7 1 27 48 381 Delwijnen 33,3 31,0 98,0 521 336 1678 88 66 42 196 11 5 37 75 9 3 42 70 382 veldriel 40,7 34,4 110,1 736 386 1986 65 41 38 144 14 "6 31 71 9 3 49 77 254 Biesboseh 41,1 40,1 118,1 914 466 2375 96 48 44 188 14 6 16 57 6 1 45 60

Loess 130 Spauheek 38,6 41,6 112,9 642 472 1936 108 33 18 159 10 3 6 40 2 3 15 40 129 Beek 38,9 35,8 108,2 697 414 2019 76 38 26 140 11 2 10 36 4 1 12 42 260 Boneveld 39,8 35,4 106,1 796 431 2067 120 35 30 185 7 2 15 51 8 2 27 55

N 1TI 1TI

Experimen tal fields continued 268 Scheemda 32,1 36,1 99,6 586 490 1936 68 28 22 118 11 3 22 62 8 3 36 65 269 + K day 41,5 36,2 112,7 1350 539 2891 104 34 24 162 56 38 1, 36 14 7 16 53 274 P Zijl 38,5 31,5 110,4 553 352 1906 80 34 16 130 10 5 16 40 8 4 18 45 275 + K loam 39,5 29,7 107,7 718 350 2048 88 37 16 141 16 11 12 40 9 4 17 44 3070uddorp 35,2 33,4 105,5 513 382 1833 40 9 8 57 6 3 9 22 4 2 8 34 311 + K loam 37,0 36,6 107,6 788 450 2167 49 10 8 67 18 6 tr 8 6 4 6 32 270 E. Compascum 34,9 32,9 100,5 345 345 1616 12 4 1 17 4 1 2 9 4 1 2 9 271 + K sandy peat 35,6 29,6 98,1 553 379 1756 17 6 1 24 11 6 1 6 6 2 2 8 286 Marum (peat) 35,5 30,7 103,4 369 306 1406 12 3 2 17 16 11 4 9 10 10 5 10 287 +K 39,7 34,0 108,5 367 329 1506 16 4 2 22 18 14 2 4 11 10 4 9 1

300 Hooghalen 35,2 29,5 96,8 360 378 1538 10 4 3 17 4 1 3 4 3 1 6 91

305 + K sand 36,3 31,5 103,0 548 387 1795 26 6 3 35 23 16 2 2 5 2 5 8 1

338 Erp 36,9 30,8 100,4 452 414 1648 9 2 1 12 7 4 2 10 4 3 2 10! 339 + K sand 29,6 29,0 93,5 680 421 1941 19 3 1 23 17 10 tr 9 4 3

2 101 Various clays 11 G lauconite-N etherl 42,6 47,5 129,2 1614 1389 4619 998 228 164 1390 12 10 7 56 7 5 12 60 8 Illite-N etherl. 39,5 21,0 82,0 1258 484 2476 32 22 20 74 11 2 6 48 7 2 15 59 113 Adobe USA 35,8 30,0 103,9 2075 394 3577 210 30 16 256 8 10 +24 +18 8 4 16 24 173 G lacial Finland 33,6 40,5 103,4 1409 794 3112 188 30 16 234 8 7 40 78 10 6 47 82 155 Tzcherno USSR 38,9 28,7 100,9 793 430 2152 222 108 58 388 20 10 18 45 16 3 48 60 422 Tir Noir Marocco 40,8 26,8 97,8 714 412 1877 106 90 78 274 15 5 38 47 7 3 40 50

Con trol Quartz 32,7 27,0 93,4 306 357 1488 2 tr tr 2 1 tr tr tr tr tr tr tr Quartz 32,8 34,3 100,4 305 319 1436 1 tr tr 1 1 tr tr tr tr tr tr tr Quartz 33,1 26,2 90,4 295 332 1451 2 tr tr 2 1 tr tr tr tr tr tr tr

Manuring in kg K20 /ha : Scheemda: 4050 (22 years) I Erp : ~ 750 (7 years) I Marum : 440 (2 years) I Ouddorp : 2500 (10 y) P. Zijl : 2700 (15 years) Hooghalen : 2070 (22 years) E. Compascum : 1700

(19 y). From : J. M. M. van den Broek and H. W. van der Marel (1964). The alluvial soils of the rivers Meuse, Roer and Geul in the province of Limburg. Meded. Stichting voor Bodemkartering, No. 7, 83 pp.

6. POTASSlUM FIXATION INCREASED BY EXHAUSTION WITH CROPS

Another way to increase K-fixation in a soil is by eropping. As a result of the exhaustion of the soil by plants, there will be a widening ofillite ofbiotite layers-Mortland et al (1956),Morländer (1957),Gris­singer & Jeffries (1957), Welte (1962); Conyers (1968), Malquori (1975), Ristori (1975).

Table 4 gives the results of an experiment with pots in which oats were cultivated thirteen times consecutively. The data shows that the K-manured soils have larger amount for mg K20 in the harvested plants and for K20 in the 25 % and 0,1 n Hcl soil extract, but lower amounts of fixed K (wet and dry) than the non manured samples. Potassium fixation af ter the erop ping has largely increased; in particul­ar K-fixation data af ter the wet method are higher. The increase de­pends on the K-reserves in the soil and the amount of K-fixation be­fore cultivation - van den Broek & van der Marel (1964).

7. POTASSlUM FIXATION DECREASED BY K+ AND NH1 SALTS

Potassium fixation can be ieduced by addition of K +, NHt, Rb + or Cs + ions, which have diameters of about the size of potassiurn, and in addition have a high polarizability .(see chapter 10).

The decrease in K-fixation is larger in the wet method than in the dry method. It can happen that a sample has 71 % fixation af ter the dry method, but none determined af ter the wet method (see table 5).

For the increase of K20 dissolved by 0.05 n HCI + 0,1 n HCI + 10 % HCI has been found 5295 kg K20jha, or 64 % of the total amount of K20 applied during 18 years - for details: Van der Marel & Venekamp (1955). The total manure application has been 8217 kg or 456.5 kg K20/ha yearly on average. .

The amount of K fixed from the applied manure is 8217 kg - 3930 kg (exchangeabie K) - 1200 kg (K in crops and in drainage) = 3087 kg or 38 %.

The figures show that for exchangeable K and for K in 0.05 HCI + 0, 1 n HCI + 10 % HCI, the applied K manure has not moved further than a depth of 10-25 cm. Wet fixation shows the same picture. In the dry fixation is only a small decrease for the 0-5 cm sample (from 81 to 63 %).

When the bulk of the plant roots go deeper than 25 cm, as in or­chards, there is astrong hindrance for K+ to be adsorbed by the plant. K+ and NHt fixation proceeds along the same way and at equal degree­Chaminade and Drouineau (1936), Page & Baver (1940) Levine

256

tv (J1 .......,]

K20 exchangeable and K20 dissolved by HCI of various strengths in prome samples of the not manured object from orchard "De Lan­ge Ossenkampen" at Wageningen

Description not manured manured difference m~nured not manured K20 in 0.001 per cent K20 in 0.001 per cent K20 in 0.001 per cent K20 in kg/ha

o- s- 10- 25- 50- 75- O- S- 10- 25- 50- 75- O- S- 10- 25- 50- 75- O- S- 10- 25- 50- 75-5 10 25 50 75 1005 10 25 50 75 1005 10 25 50 75 1005 10 25 50 75 100

tExchangeable K20 in successive percolations with 0.5 N Mg-ace ta te First 250 cc 5 4 3 2 2 1 304 190 63 2 2 1 299 186 60 0 0 0 1495 930 900 o 0 0 Second 250 cc 3 1 1 1 1 1 31 23 :14 1 1 1 28 22 .13 0 0 0 140 110 195 o 0 0 Third 250 cc tr tr tr tr tr tr 8 7 4 1 tr tr 8 7 4 1 0 0 40 35 60 25 0 0

Total 8 5 4 3 3 2 343 220 81 4 3 2 335 215 77 1 0 0 1675 1075 1155 25 0 0 L = 3930

Acid soluble K20 in successive percolations with Hel of various concentrations 0.05 n Hel First 250 cc 9 6 5 5 4 2 346 227 79 6 4 2 337 221 74 1 0 0 1685 1105 1110 25 0 0 Second250 cc 8 5 4 4 4 2 84 22 15· 5 4 2 16 17 11 1 0 0 80 85 165 25 0 0 Third 250 cc 9 2 2 2 2 1 11 7 5 2 2 2 2 5 3 0 0 0 10 25 4:? o 0 0

Total 26 13 11 11 10 5 381 258 99 13 10 6 355 243 88 2 0 0 1775 1215 1320 50 0 0 L = 4360

0.1 n Hel First 250 cc 1 1 1 1 1 1 6 6 3 2 1 1 5 5 2 1 0 0 25 25 30 25 0 0 Second250 cc 1 1 1 1 1 1 6 5 4 2 1 1 5 4 3 1 0 0 25 20 45 25 0 0 Third 250 cc 1 1 1 1 1 1 4 4 3 1 1 1 3 3 2 0 0 0 15 15 30 .0 0 0

Total 3 3 3 3 3 3 16 1510 5 3 3 13 12 7 2 0 0 65 60 105 50 0 0 L = 280

10 % Hel First 250 cc 6 6 7 6 4 4 21 18 12 8 4 4 15 12 5 2 0 0 75 60 75 50 0 0 Second250 cc 6 6 6 6 4 4 16 15 13 9 4 4 10 9 7 3 0 0 50 45 105 75 0 0 Third 250 cc 4 4 4 4 4 3 9 9 7 5 4 3 5 5 3 1 0 0 25 25 45 25 0 0

Total 16 16 17 16 12 11 46 42 32 22 12 11 30 26 15 6 0 0 150 130 225 150 0 0 ~ = 655

Potassium K20 fixed in per cent K20 flXed in per cent kind of K20 by which the K-manured soil ·soillayer in cm. fixation has enriched 0-25 25-100 '0-100 i

Wet method 47 64 67 80 80 68 0 o 20 81 82 70 K 20 exchangeable in kg/ha 3905 25 3930 I

diff. in % of total K20 applied in manure 47.5 0.3 47.9 !

Dry method 81 81 85 85 87 85 63 71 76 86 87 85 K20 in 0.05 Hcl+0.1 NHCI+10% HCI in kg/ha 5045 250 5295 I

- - -- - - - - - - - - - - - - --- - -

Volume soil sample is assumed to be = 1.2; tr = traces; depth sample in cm; total ·appli~d K20 = 8217 kg K20/ha in 18 years (yeady = 456.5 kg/ha as an average) in % of tota!. K20 applied in manure 61.4 3.0 64.5. From H. W. van der Marel & J. T. Venekamp (1955). Onderzoek naar het verschijnsel der kalifixatie in de Nederlandse gronden. Versl. Landbouwk. Onderzoekingen no. 61.8, 61 pp.

N lil 00

Table 6

Adsorption capacity for Na + and NH4+ ions in (me/lOOg) for samples < 2 J1. at several depths (cm) of soils from the Meuse region, VermÎculite and other soil samples

Na+ Na~/ No. Location Na+ NH+ NH+ No. Location Na+ NH + NH +

4 4 4 4

Vermiculite (samples powdered) Illite (samples < 2 J1.) 429 Pennsylvania, USA 97.6 39.6 2.46 414 Illinois, USA 31.9 28.9 1.10 1147 Australia 93.7 47.5 1.97 22 Grundite, USA 34.3 30.3 1.13 1302 Nyassaland 98.7 35.2 2.80 723 Fithian, USA 28.1 23.3 1.21 2198 Rhodesia (impure) 32.7 10.8 3.03 Glauconite (samples < 2 J1.) 713 Teheran 88.7 46.4 1.91 10 SIenaken, Holland 33.2 29.4 1.13 1269 Kenya 112.8 75.0 1.50 . 999 Parécourt, France 51.9 45.8 1.13

Meuse Region (samples < 2 J1.) 217 . Nw. Jersey, USA 53.9 47.4 1.14 113 Trois points, all 90/95 51.9 43.0 1.21

Montmorillonite (samples < 2 J1.) 162 Landelies, all 60/80 60.0 49.2 1.22 165 Landelies, all 50/65 47.4 38.4 1.23 641 Wyoming, USA 91.3 85.3 1.07

168 Lobbes, all 25/45 62.3 51.4 1.21 643 Chambres, USA 43.5 40.5 1.07

169 Lobbes, all 50/70 63.9 51.6 1.24 320 Otay, USA 106.0 104.8 1.01

517 Roosteren 0/10 (mud) 41.6 34.3 1.21 605 Polkville, USA 98.2 95.6 1.03

912 Hedel, (mud) 0/10 32.2 25.8 1.25 MainlySoil Montmorillonite (samples < 2 J1.) 302 Haelen, all 0/20 53.2 44.5 1.20 646 Badob,Soudan 76.6 74.2 1.03 305 Haelen, all 50/70 55.3 45.0 1.23 644 Black soil, Bombay 87.9 86.1 1.02 796 De Hoeve, all 0/30 67.3 55.0 1.22 2197 Black soil, Rhodesia 94.5 88.5 t.07 447 Kerkwijk, all 0/30 62.5 53.0 1.18 474 Black soil, E thiopia 74.5 69.6 1.07

--

I

(1941 ),Barshad (1951). The K+ and NH! cations have about the same diameter (1.33 R

and 1.34 ~ and have a high Eolarizability (àD = 0.97 R3 and 1.604 R3; Na = 0.21 R3, Ca = 0.44 R ). The effect ofK+ or NH4 fixation is a decrease in cation exchange capacity Kolodny (1938), Peters on &

Jennings (1938), Truog & Jones (1938), Joffe & Kolodny (1939). Van der Marel (1954,1959) has found that forDutch soils the ratio: total exchangeable cations/cation exchange capacity (NH! from NH4CI) may even be 1.3 for strongly K fixing soils.

From table 6, which gives the data for the ratio Na+ adsorbed/NH!­adsorbed, it appears that this quotient is very high for vermiculite (1.5-3). This mineral has the greatest amount of Al substituted for Si in the tetrahedrallayers - Barshad (1948).

F or < 2 J.L samples fr om the Me~,e region the ratio is 1.18-1. 24. For illite this ratio is 1.10-1.21, for glauconite 1.13-1.14. Montmorillonite which has a low Si/Al substitution for its tetra-

hedrallayers, fixes potassium only slightly, as is also the case for soil­montmorillonite.

8. MINERALOGICAL ANAL YSIS

Mineralogical analyses sediments < 2 J.L and rocks fr om the Meuse river and its catchment area.

In the following are the results of mica and related minerals (mus­covite, intermediate, illite, expandend illite, swelling ûlite). Quartz is a common mineral and therefore it is not mentioned. Some samples have feldspar, but in small amounts. Kaolinite is very common. In some sediments large amounts are found. Magmatic chlorite is also widespread but in small amounts;however, when badly crystallized (soil chlorite) it is difficult to distinguish. Illite occuring in sediments together with muscovite cannot be distinguished. Thus these two minerals where taken together and indicated as illite. This name is chosen and not muscovite because illite is always fine (secondary day mineral) and muscovite is usually coarse.

8.1. SEDIMENTS OF THE CATCHMENT AREA OF THE MEUSE RIVER IN BELGIUM

8.1.1. Ardennes region

Eupen, Bar. Michel, Long Faye, Malmedy, Bar. Fraiture" La Roche, Mon Champs, Champlain, Bellevaux, Bande, Annevoie, Nessonvaux. The main mica comp"onent in this region is illite (mica). Some samples have also some intermediate: Champlain, Nessonvaux. The grey

259

shale fr om Bar. Fraiture has ca 15 % chlorite. In the podzol profile of Long Faye kaolinite has somewhat accumulated in the B-horizon.

8.1.2. Famenne region

S hales shallow weathered Barvaux, Nettine, Heure. The main mica mineral is illite (mica). The soil sample from Heure

has more kaolinite as usual. The rock sample investigated is a chlorite schist with ca 40 % chlorite.

Limestone, shallow weathered Marche en Famenne, Han-sur-Lesse, Nettine. These soil samples have mainly illite (mica) with some intermediate

and expanded illite (swelling illite). The residual of the rock sample from Nettine when treatedwith HCI, delivers mica (illite),i~termediate! and quartz.

8.1.3. Condroz region

Deeply weathered shales Falisolle, Borsu, Fontenoy, Haute Folie, Louveigné, Aywaille, Ho­

dimont. The samples mainly contain illite. Lou~~igné thereby has some inter­

mediate. The black houiller schist fr om , Falisolle has more kaolinite than usual and Aywaille and Hodimont have more chlorite.

Deeply weathered psammites Fontenoy, Fosse, Nannine, Evieux, Montfort, Steuvere, Pessoux,

Ohey, Haute Folie, Hotchamps, Annevoie, Hoyemont, Sly, Hody. The samples mainly contain illite. Some have thereby intermediate (Fon­tenoy, Fosse, Steuvere, Pessoux, Haute Folie), or have expanded illite, (mica) (Fontenoy, Hoyemont, Sly, Hody).

The < 2 IJ. separate of the sandy subsoil (at ca 400 cm) fr om Nannine has much kaolinite. The samples from Fontenoy, Haute Folie (with loessial topsoil) have some more kaolinite as usu al and that of Hodi­ment and Annevoie have some more chlorite.

The weathered psammite from Annevoie and Hodimont .have 10-15 % feldspar.

Deeply, weathered calcareous psammites Ouffet, Hody. All the samples have illite and intermediate. The last has ca. 15 % kaolinite and has also some expanded illite.

260

Deeply weathered marly grès (shale) Méan. The sample" contains mainly intermediate.

Deeply weathered marly sandstone Chardeneaux, Hody: The samples mainly contain intermediate.

8.2. SEDIMENTS OF THE TRIBUTARY RIVERS OF THE MEUSE FROM LIMBURG, GERMANY AND BELGIUM

Roer, (Odiliënberg, Mehlick, Vlodrop ), Geul (Kapolder, Party, Car­tiels), Amblève (Trois Points), Ourthe (La Roche, Hotton, Barveau, Hamoir, Esneux, Samson), Lesse (Lessive, Anserenne), Sambre (Na­mur, Ham, Landelies, Lobbes).

The principal mineral is mica. The samples from the Sambre (Namur, Ham, Landelies, Lobbes) all have also interstrafied minerals. Some chlorite (Amblève, Ourthe) is also a common component. Swelling minerals are absent.

The grès (slate) rocks from La Roche and Barveaux have mica. The basin soil from Landelies only coritains intermediate and not expand­ed or swelling illite. The sandy samples gathered at the border of the Ourthe at La Roche have about 20 % chlorite. The composition of the tributary river sedimen"ts of the Meuse river in the Netherlands and Ge~any (Roer and Geul) are mainly the same as that of the Meuse river i.e., quartz = 10-15 %, mica = 15-20 %, chlorite = 5-10 %, feld­spar = 5-10 %, open illite (expanded illite, swelling illite) = 30-40 %, kaolinite = 15-20 %.

Only the Roer samples have more mica and chlorite, but some less expanded illite (swelling illite) - Van den Broek & van der Marel (1964).

8.2.1. Sediments of the Meuse river in Belgium

Lanoy, Hermall, Ben Ahin, Andenne, Jambes, Profondeville, Yvoir, Hastière, Freyer, Waulsort, Heer.

The samples investigated have mica and mostly thereby inter­mediate. small amounts of calcite are also a common component.

The basin soils at Lanoy, Hastière, Andenne and Freyer have inter­mediate, expanded illite, swelling illite.

8.2.2. Sediments of the Meuse (Waal) river in the Netherlands

Sleeuwijk, De Hoeve, Zuilichem, MaurikseWetering, Aalst, Kerk­wijk, Heusden, Veldriel, Hedel, Ammerzoden, Lith, Alem, Bruchem, Garneren, Kessel, Buggenurn, Maasbracht, Grevenbicht, Roosteren,

261

Borgharen, Haelen, Bunde, Itteren. Many samples have, besides illite and intermediate, also expanded

and swelling illite : Kerkwijk, Heusden, Veldriel, Hedel, Ammerzoden, Lith, Alem, Bruchem, Kessel, Maasbracht, Roosteren, Haelen.

Many samples downstreams Nijmegen at ca. 10-15 km from the Meuse river, are more or less defiled with Waal (Rhine) sediments. Up­stream Nijmegen the distance between the two rivers increases rapidly.

As the sediments are mostly fine (basin soils) they have a bad reputation in agricutlural practice. Muds of the Meuse (Rhine and Waal) have mostly small amounts of calcite and dolomite, Van der Marel (1950).

8.2.3. "Biesbosch" and tidal !loods sediments of the Meuse (Waal) river in the N etherlands

Oosterkil, Spijkerboor, De Lepelaar, Waalwijk, Bakkerskil, Janne­zand, Amerplaat, Nw. Merwede, Brouwershaven.

Swelling illite Is an exception (Spijkerboor, De Lepelaar, Bakkers­kil, Amerplaat). Illite intermediate and expanded illite are common, also calcite especially in the coarser samples. Calcite to ca. 20 % is found in the glacial sands below 10-15 mtrs. The calcite found is main­ly of shells.

8.2.4. Brackish muds and polders, Meuse, Schelde, Lauwerssea and Dollard Sediments

Waarde, Woensdrecht, Bergen op Zoom, Antwerpen, Gent, Lillo, Ho­boken, Rupelmonde, Dendermonde, Lauwerssea, Dollard, Winsum.

The muds investigated show illite, intermediate,swelling illite . and some calcite (shells). The polder soils from Gent, Antwerpen, Lillo (Schelde) and Veurne (marine polder) have swelling illite. Probably the latter is formed from the first - see also Van Ruymbeke (1964). The swelling illite (soil montmorillonite) in the muds of the Schelde river come from tertiair calcareous sediments in the hinterland.

9. DISCUSSION

The results show that there is only a very limited amount of swell­ing K-fixating illite mineral in the soils of the catchment area of the Meuse. Expanded, non swelling minerals are more frequent. The most common minerals are illite and intermediate, especially the lat ter. As a consequence the swelling illite found. in large amounts in the Meuse delta deposites must have another origin. It is known that wet and swamp conditions are important for the formation of swelling mica

262

minerals, whereby interlayer charge is partly lost by hydrox:ylation (0 replaced by OH), by oxidation (Ferroto Ferri of octahedral iron) or by silification (tetrahedral Al3+ replaced by Si4+ -see J ackson et al 1952), because of the larger energy constant of Si-O than Al-O (3.123 and 1. 793 kcal/mole, resp. Keller, 1954). In addition there is a replace­ment ofhighly polarizable K+ by less polarizable cations like (H30)+, Ca++, Mg++. The resulting 14.R mineral swells easily when treated with an excess of glycerol or another solution ofhigh hydrogen bonding capacity. When treated with an excess of a strongly polarizable cation (KCI or NH4CI) it contractsitslayers to 10.R (tabie 7, figures 5 & 6).

The degree of swelling with water or glycerol and contraction with K+ or other cations depends on particle size, interlayer charge (Al-Si substitution) and polarizability of the cations.

Vermiculite has the highest charge and therefore its contraction capacity upon treatment with K+ or NH4+ solutions is highest; common montmorillonite shows the weakest capacity. Reversely vermiculite has the smallest swelling power when treated with glycerol, montmorillonite the highest.

Therefore, not only one well defined mineral of constant behaviour will be occurring but a series of minerals with variabie K contracting and glycer?l expanding properties. They are called swelling illites or ammersoites - van der Marel (1952, 1954 )"

Swelling illite is very of ten mistaken for common montmorillonite or for soil montmorillonite because of its similar physical properties. However the genesis of the two groups of minerals is different.

An analogous situation, as signalized for the Meuse sedimen ts, is found for the Nile delta. The Ethiopian plateau, which is considered as the main source of the Nile sediments, consists of weathering pro­ducts of basic igneous rocks. The < 2 Jl illite and soil montmorillonite pa~ticles are carried down the Nile over hundreds of miles and deposit­ed in the delta. In stagnant water the illite is gradually transformed in­to swelling illite during thousands of years.

Intermediates and expanded illite are intermittant stages in this weathering process. Continuous leaching of soil samples from the plateau with C02 saturated water during 8 months gives analogous results (Hamdi, 1959, 1960) - see also Weir et al (1975).

This transformation of illite also occurs eàsily by leaching with CaCl2 and by exhaustion with crops. This is not the case for musco­vite where the transformation mostly ends at the intermediate stage. It is caused by random substitution of Al by Fe and Mg.

Another cause is that in trioctahedral mica minerals (biotite), the interlayer cation is nearer to the H than in dioctohedral minerals.

263

Cation

Table 7

Kind of cation and glycerol on spacings of several soil types. Radius in Kaf ter Pauling (P) and Goldschmidt (G) and Polarizability in (aD) in K 3) af ter Böttcher and Scholte

Nile Kerk- Veld- Ammer- Haelen Osse- . Vermiculite Radius delta riet zoden Meuse K

Polariz. wijk kamp

Tetuan Chester aD Meuse Meuse Meuse Rhine P-G . in K3

Original 14.8 14.2 14.2 14.2 14.0 14.2 14.1 14.2 Li+ 12.8 12.8 14.2 13.2 0.60-0.78 Na+ 13.6 13.2 0.95-0.98 K+ 12.8 10.5 12.2 10.2 10.0 10.0 11.7 10.2 . 1.33-1.33 Rb+ 10.8 10.4 11.3 1.48-1.49 Cs+ 10.8 10.7 11.6 1.69-1.65 Mg++ 14.4 14.4 14.4 14.6 0.65-0.78 Ca++ 14.6 14.2 14.2 0.99-1.06 Sr++ 14.0 14.0 14.2 13.8 1.13-1.27 Ba++ 12.2 13.2 13.6 13.6 1.35-1.43 NH + 11.4 12.0 12.6 10.8 11.5 10.2 1.43 H+ 4

14.4 14.2 0.04 Glycerol 18.4 18.6 18.4 18.6 17.8 17.8 14.2 14.2 3500

5500 14.2 10.0 10.0 10.0 10.0 14.2 10.2

9.8 10.0 9.8 9.9 9.9 9.7 9.7

Pauling L., (1940). The nature of the chemical bond and the structure of mole­cules and crystals. Cornell Univ. Press, New Vork.

Goldschmidt V., (1929). Crystal sturcture and chemical constitution. Trans. Faraday Soc. 25, 253-283.

Bötcher C. J. F., (1946). Computation of the radius and the polarizability of a number of ions. Rec. trav. Chim. 65, 19-38.

Böttcher C. J. F. & Scholte Th. G., (1951). The polarizabilities and the radius of ions in solution. Rec. Trav. Chim. 70, 209-235.

Another source of K-fixation in the Meuse delta sediments may be attributed to biochemical action. This may create illite-like minerals with badly developed structures and with strong potassium fixing and swell capacities ("Hudig"-marsh illites). This type of mica day mineral is found in discernable quantities only in deep swamps with large accumulations of organic matterjfor details Hudig et al (1963).

264

0.02 0.21 0.97 1.47 2.37

±0.02 0.44 0.84 1.63 1.60

Counts/sec. orbitrary units

9.7 I

7. 08

10

Vermiculite 429

W.Chester U.SA

550·

9.8 I

10 15

K:kaolinite, Chl:chlorite, l:illite, It :intermediate, Sm :soilmontmorillonite

Fig. 5

9.5

Montmo -rillonite

344 Boyord

14 .6 I

17.7 I

28 Degrees CO-KO<l <X

2: 1.787 A

10

X-ray diffraction spectra of venniculite, soil montmorillonite and common mont­morillonite treated in several ways.

265

I ntensity_ Counts/sec. o rbi t rory units

302 Haelen basinsoil Meuse delta

871

10 10

K=koolinite, Chl=chlorite, I=illite, It =intermediote, SwI = swelling illite

Fig. 6

X-ray diffraction spectra of swelling illite treated in several ways.

550'

266

REFERENCES

1. Introduction

Polak B. Not published.

PostrnaH., (1957). Balans van het slibtransport in de Nederlandse rivieren en langs de kust. Rapport werkgroep Slibtransport Zoölogisch Station, Den Helder. No. 1957-1 , 18 pp.

Temme J. & van der Marel H. W., (1952). Potassium ftxation and disturbed potassium condition. Versl. Landbouwk. Onderz. No. 58.6, 53 pp.

Van den Broek J. M. M. & Maarleveld G. c., (1964). The late pleistocene deposit of the Meuse. Meded. Geol. Stich. nwo serie 13-24.

Van den Broek J. M. M. & van der Waals L., (1967). The late tertiair peneplain ofSouth Limburg (the Netherlands) Geologie en Mijnbouw 4b (91, 318-332).

Van der Marel H. W., (1954). Potassium ftxation in the Dutch Soils. Mineralogical analysis. Soil Science 70, 109-136.

2. Catchment area of the Meuse river and its tributaries

Avril P., (1957). Les sols podzoliques bruns en Ardenne BeIge. Pedologie 7, 97-10l.

De Beer E. & Deboeck W., (1948). Resultats de quelques essais effectues sur des argiles du Condroz. Silic. Ind. 13, 101-105.

Deckers J. & Van Stallen R., (1955). Contribution à l'étude de la saturation en bases des sols bruns de l'Ardenne et de la Famenne. Agricultura 3, 311-340.

Deckers J., (1957). Sols hydromorphes des hautes plateaux de l'Ardenne Belge Pedologie 7,192-198.

Deckers J., (1958). Texte explicatif de la planchette de Odeigne 179 W.

Carte des Sols de la Belgique. Centre de Cartogr. des Sols, 79 pp.

Deckers J., (1959a). Texte explicatif de la planchette de Dochamps 178E. Carte des Sols de la Belgique. Centre de Cartogr. des Sols, 92 pp.

Deckers J., (1959b). Texte explicatif de la planchette de Bihain 179E. Carte des Sols de la Belgique. Centre de Cartogr. des Sols, 89 pp.

267

Delecour F. & Philippot R., (1967). Evolution d'un profil forestier sur l'influence de la culture. Pedologie 7, 234-238.

DeIecour F. & Manil G., (1962). Mikrornorphologische Beitrag zur Kenntnis der sauren Braunerden der Belgischen Ardennen. Zeits. Pfl. Düng Bodenk, 98 (143) 219-223.

Hallet H., (1957). N ote sur un podzol déveIoppé sur rnateriaux gréseux calcifères. Pedologie 7, 189-192.

Hanotiaux G. & Bourguignon P., (1957). Minéralogie des argiles des sols Ardennais Pedologie 7, 246-250.

Henrard G., (1958). Les sols de la F amenne. Pedologie 8, 199-233.

Manil G. et al, (1953). Les sols forestiers de l'Ardenne. Le plateau de Saint-Hubert-Nassogne. Bull. Inst. Agron. Stat. Reeh. Gernbloux, 21, 43-140.

Manil G. & Pécrot A., (1954). Les sols forestiers oligothropes du climax des Ardennes Belges. Compt. Rend. V Congr. soil Sci du Sol 4, 441-446.

Manil G. & Hanotiaux G., (1957). Données descriptives sur les sols bruns acides et les sols bruns ocreux (brown pod­zolic soils) des Ardennes BeIge. Pedologie 7, 239-245.

Maréchal R., (1956). Texte explicatif de la planchette de Ciney 167 E. Carte des Sols de la Belgique, Centre de Cartographie des Sols, 76 pp.

Maréchal R., (1958). Contribution à l'étude des terrains superficieIs de la région Condrusienne. Pedologie, rnérn. 1, 320 pp.

Maréchal R., (1961). Texte explicatif de la planchette de Tavier 147 W. Carte des Sols de la Belgique, Centre de Cartographie des Sols, 97 pp.

Pécrot A. & Avril P., (1954). Les sols Ardennais I, Etude rnorphologique et génétique des sols bruns acides et des sols bruns podzoliques du Plateau de Saint-Hubert. Bull. Inst. Agm. Stat. Reeh. Gernbloux, 22, 52-95.

Scheere G., (1959). La kwalinite du Houiller Beige. Silie.Ind. 24,475-483.

Schroeder D., (1955). Tonminerale rnit Wechsellagerungsstruktur im Lösz.

268

Zeitschrift. PjZ. Düng. Bodenk. 70 (115), 17-22.

Tavernier R. & Maréchal R., (1957). Les sols à Fragipan de la region Condrusienne. Pedologie 7, 199-203.

Tavernier R. & Maréchal R., (1958). Carte des associations de sols de la Belgique. Pedologie 8, 134-182.

Temme J. & van der Marel H. W., (1952). Potassium fIXation and disturbed potassium condition. Versl. Landbouwk. Onderz. No. 58 6, 53 pp.

Van den Broek, J. M. M. & van der Marel H. W., (1964). The alluvial soils of the Meuse, Roer and Geul in Limburg. Boor en Spade Vol. 13. Nr. 7, 83 pp.

Van der Marel H. W., (1954). Potassium fIXation in the Dutch soils. Mineralogical analysis. Soil Science 70, 109-136.

Van der Marel H. W. & Venekamp J. T. N., (1955). Onderzoek naar het verschijnsel van de kalifixatie in de Nederlandse gronden. Versi. L. O. No. 61.8, 61 pp.

Van Straaten L. M. J. U., (1954). Sedimentology of recent tidal flats deposits and the Psammites du Condroz (Devonian). Geol. en Mijnbw. 16, 25-47.

Weaver ch. E., (1959). The day petrology of sediments. Proc. 6th Internatl. Conf Clays and Clay Minerals (1957),154-187.

3. Methods of analysis

Van der Marel H. W., (1954). The amount of exchangeable cations of K-fixating soils. Transact. Vth. Intematl. Congr. Soil Science Léopoldville. Vol. 11, 300-307.

Milne I. H. & Warshaw ch. M., (1956). Methods of preparations and control of day minerals specimens in X-ray diffrac­tion analysis. Proc. 4th Natl. Conf Clays and Clay Minerals (1955), 22-30.

4. Potassium fixation increased by leaching with salts

Caillère S., Hénin S. & Guennelon R., (1949). Transfonnation experimentale du mica en divers types de mineraux argileux par separation de feuillets. C. R. Acad. Sci. 228, 1741-1742.

Hamdi H., (1959). Alterations in the day fraction of Egyptian soils. Z. PjZ. Ernähr. Düng. 84,204-211.

269

Rivière A., (1948). Sur les illites et les argiles Bravaisitiques. Verre et Silic. Ind. 13, 47-48 .

Weiss A., Mehler A. & Hofmann U., (1956). Kationen austausch und innerknistalliner quellungsvermögen bei den Mineralen der Glimmergruppe. Zeits. Neturf. 11, 435-438.

White J . L., (1951). Transformation of illite into montmorillonite. Proc. Soil Sci. Soc. Amer. 15, 129-133.

Wiklander L., (1950). Fixation of potassium by clays saturated with different cations. Soil Sci. 69, 261-268.

5. K-fixation increased by exhaustion with crops

Conyers E. S. & McLean E.O., (1968). Der einfluss der Entzüge von nativen und zugeführten K aus Tonen durch Pflanzen auf die Stroktur der Tonmineralen. Proc. Soil Sci. Soc. Amer. 32, 341-345.

Grissinger E. & Jeffries C. D., (1957). Influence of continuous cropping on the flXation and release of potassium in three Pennsylvanian soils. Proc. Soils Sci. Soc. Amer. 211 (1956) 409-412.

Malquori A., Ristori G. & Vidrich V., (1975). Biologische Verwitterong von Kalisilikaten. I Biotit. Kali Briefe 51 Folge. No. 3,1-7.

Mortland M. M., Lawton K. & Uehara F., (1956). Alteration of biotite to vermiculite by plant growth. Soil Sci. 82, 477-48l.

Morländer M. M., Lawton K. & Uehara G. , (1957). Alternation of biotite to vermiculite by plant growth. Soil Sci. 82,477-481.

Ristori G. G., (1975) . Untersuchungen über die Freisetzung von Kalium des Biotites, Orthoklases und Leuzites durch die Pflanzen. Kali Briefe 53, Folge, No. 9, 1-1l.

Van Broek J. M. M. & van der Marel H. W., (1964). The alluvial soils of the rivers Meuse , Roer and Geul in the province of Limburg. Meded. Stichting Bodemkartering No. 7, Wageningen, 83 pp.

Welte E., Niederbrudde & Werner W., (1962). Zum Kalium Dynamik illitreicher Auelehme bei intensivez Bepflanzung. Zeits. Pfl. Düng Bodemk. 96, 157-169.

270

6. Potassium fixation decreased by K+ and NH; salts

Barshad 1., (1948). Vermiculite and its relation to biotite as revealed by base exchange reactions, X-ray analysis, differential thennal curves, and water content. Amer. Minera133, 655-678.

Barshad 1., (1951). Ammonium fIXation and its relation to potassium fixation and to determination of ammonium exchange capacity. Soil Sci. 72, 361-371.

Chaminade R. & Drouineau F., (1936). Recherches sur la méchanique chimique des cations exchangeables.

Joffe J. S. & Kolodny L., (1939). The effect of alternate drying and wetting on the base exchange complex with special reference to the behaviour of the potassium ion. Proc. Soil Sci. Soc. Amer. 3, 107-111.

Kolodny L., (1938). The mechanism of K-fIXation in soils and the availability of fixed potassium to plants. Thesis Rutgers Univ. Nw. Brunswick.

Levine A. K., (1941). A further study of the relation of K-fIXation to the exchange capacity of soils Thesis Rutgers Univers. New Brunswick,

Page J. B. & Baver L. D., (1940). lonic sizes in relation to fixation of cations by colloidal day. Soil Sci. Soc. Amer. Proc. (1939) 150-155.

Peterson J. D. & Jennings D. S., (1938). A study of the chemical equilibrium existing between soluble and base exchange compounds. Soil Sci. 45, 277-298.

Truog E. & Jones R. S., (1938). Fate of soluble potash applied to soils. Ind. Eng. Chem. 30, 882-885.

Van der Marel H. W., (1954). The amount of exchangeable cations on K-fixating sols. Transact. 5th congr. Soil Sci. Leopoldville 2, 300-307.

Van der Marel H. W., (1959). Potassium fIXation a beneficial soil characteristie for erop produetion. Zeits. Pjl. Düng, Bodenk. 84 (129) 57-62.

Van der Marel H. W. & Venekamp J. T. N., (1955). Potassium fIXation in the Dutch soils. Verslag Landbouwkundige Onderz. no. 61.8, 61 pp.

271

7. Mineralogical analysis

Van den Broek J. M. M. & van der Marel H. W., (1962). The alluvial soils of the rivers Meuse, Roer and Geul in the Province of Limburg. Meded. Stichting Bademkart No. 7 Wageningen 83 pp.

Van der Marel H. W., (1950). Calcite and dolomite in the day faction of the Dutch soils. Landbk. Tijdschrift 62, 300-306.

Van Ruymbeke, (1964). Bijdrage tot de studie van de kleimineralen in de zeepolders i.v.m. kalihuishouding van deze bodems. Dissertatie Gent, 192 pp. + bijlagen.

8. Discussion

Hamdi H., (1959). Alterations in the day fraction of Egyptian soils. Z. Pfl. Emähr. Düng. 84,204-211.

Hamdi H., (1960). Transformation of the day fraction of the alluvial soils of Egypt. Ann. Agric. Sci. Caïro 2, No. 5, 135-139.

Hudig J., Beutelspacher H. & van der Marel H. W., (1964). Uber die Entstehung von biochemische Tonsedimenten in die Marschböden der Niederlanden. Z. Pfl. Emähr. Düng. Badenk. 105, 224-239.

Jackson M. L., Hseung Y., Carey R. B., Evans E. J. & van den Heuvel R. D., (1952). Chemical weathering of layer silicates. Proc. Soil Sci. Soc. Amer. 6 (1951),3-6.

Weir, A. H., Ormerod, E. C. & I. M. I. El Mansey (1975). Clay mineralogy of sediments of the Western Nile delta. Clay minerals 10, 369-386.

Summary

The amount of potassium Hxed in a soil sample when shaken, or dried with a solution of potassium chloride is largely related to two factors. The first is the amount of small soil particles, as expressed by the separates < 16 /-L or < 2 /-L. The other important factor is the type of day mineral dominant in the soil with res­pect to the electrical charge between the layers of the day mineral.

The strong K-fixation in the sediments of the Meuse delta in the Netherlands is mainly attributed to weathered muscovite, illite, intermediates and expanded mica minerals. They originate from eroded rock types of sand stones and slates in the Condroz region in Belgium on which lateritic and red-yellow podzolic types of soils developed during the Tertiary.

Swelling mica minerals (ammersoites) occu·rring in the sediments of the Meuse delta are formed by silification of the expanded mica minerals in places of poor soil drainage. An analogous example of weathering of illite to swelling illute under wet conditions is known for the Nile delta.

272

Eigenschappen en oorsprong van het Maasalluvium in Nederland en België

Samenvatting

De hoeveelheid kalium, die door een grondmonster wordt geflXeerd uit een op­lossing van KCI bij schudden of bij drogen, is sterk afhankelijk van twee factoren.

De eerste is de hoeveelheid klei-deeltjes, zoals uitgedrukt door de percentages < 2 Jl of < 16 Jl. De andere factor is het type kleimineraal met betrekking tot de

. elektrische lading tussen de open platen van het mineraal. De sterke K-flXatie in de sedimenten van de Maasdelta in Nederland moet

hoofdzakelijk toegeschreven worden aan de aanwezigheid van verweerde musco­viet, illiet en aan intermediates en open illiet. Deze zijn afkomstig van verweerde zandsteen en schalies in de Condroz in België, waarop gedurende het Tertiair late­ritische en rood-gele podzolische bodems zijn ontwikkeld.

Zwellende mica mineralen (ook ammersoieten genoemd), die voorkomen in de sedimenten van de ~aasdelta, zijn gevormd door silificatievan de open illiet op plaatsen met slechte drainage. Een analoog proces is bekend voor de verwering van illiet tot zwellende illiet onder natte omstandigheden in de Nijldelta.

Propriétés et origine des alluvions de la Meuse au Pays-Bas et en Belgique

Résumé

La quantité de potasse, flXée par un échantillon de sol à partir d'une solution de KCl, en secouant ou en séchant, dépend essentiellement de deux facteurs.

En premier lieu de la quantité de particuies argileuses, comme exprimée par Ie pourcentage < 2 Jl ou 16 Jl. L'autre facteur est Ie type de minéral argileux en re­lation avec la charge électrique entre les feuillets ouverts du minéral.

La forte flXation de K dans les sédiments du delta de la Meuse au Pays-Bas doit être attribué principalement à la présence de muscovite altéré, d'illite, de forme intermédiaires et d'illite ouvert. Ces minéraux proviennent de grés et shistes altérés du Condroz (Belgique) sur lesquels se sont développés au cours du Tertiaire des sols latéritiques, podzolisés, rouge-jaunatre.

Des minéraux micasés gonflants (ammersoites), qui apparaissent dans les sédi­ments du delta de la Meuse, sont formés par silification d'illite ouvert à des en­droits mal drainés. Un processus analogue est connu pour l'altération d'illite en illite gonflant en conditions humides dans la vallée du Nil.

273

I PEDOLOGIE, XXX, 2, p. 275-281,2 fig. Gand, 1980.

MATIERES ORGANIQUES AU MICROSCOPE ELECTRONIQUE

A. RASSEL F. DELECOUR

1. INTRODUCTION

L'un d'entre nous a eu, naguère, l'occasion de faire, à cette même tribune, quelques commentaires sur la distribution du carbone et de l'azote dans les fractions humiques des sols bruns acid es (Delecour, 1975). Un travail plus fondamental sur les caractéristiques physico­chimiques de ces substances a été publié ailleurs (Prince Agbodjan & Delecour, 1975).

La conclusion principale de ces études était que les différences entre les divers types d'humus ne tiennent pas à la nature chimique des con­stituants mais plutot à leur mode et à leur degré d'agencement entre eux et avec les colloïdes minéraux.

L'étude par microscopie électronique des fractions humiques a été entreprise dans Ie but de mettre en évidence des différences éventuel­les de structure intime entre les divers humus.

Le but de la présente note est de présenter quelques premiers exem­pIes d' 0 bservations.

2. MATERIEL ET METHODES

Les échantillons proviennent des horizons hémiorganiques Ahl des stations décrites précédemment (Delecour & Prince Agbodjan, 1975), à humus s'étageant de la forme mull oligotrophe à la forme dysmoder.

Communication présentée à la tribune de la Société BeIge de Pédologie, Ie 16 jan­vier 1980.

A. Rassel- Chef de travaux, Station de Chimle et Physique Agricoles de l'Etat, C.R.A., Gembloux, Belgique. F. Delecour - Centre de Recherche et de Promotion F orestières - Section Pédologie (I.R.S.I.A.), Dir. Prof. G. Hanotiaux - Service Science du Sol- Faculté des Sciences Agronomiques de l'Etat, Gembloux, Belgique.

275

o o '-0 00

~

v '"Ó ::; 0 (I)

~ .-c 0Ïl

ü:

276

(I)

V ::; 0"'

's ::;

.J:: (I)

v '"Ó 'U ~

Le fractionnement de la matière organique a été opéré selon la technique de Gascho & Stevenson (1968); les extraits ont été concen­trés sous vide et lyophilisés, pour obtenir les acides fulviques (AF) et humiques (AH) sous forme solide.

En vue des observations microscopiques, les échantillons ont été pulvérisés au mortier, mis en suspension dans l'eau et soumis aux ultra­sons à 1 Mhz. Pour la microscopie à transmission, ces suspensions sont reprises aux ultrasons mais sous une fréquence de 3 Mhz, ce qui pro­voque une vaporisation intense et les particules en suspension sont re­cueillies sur une grille en cuivre, recouverte de formvar, Ie tout étant ensuite séché à l'air. Pour la microscopie à balayage, 1 gouttelette de la suspension à 1 Mhz est déposée sur un bloc en laiton et séchée à l'air.

3.0BSERVATIONS

Les premières observations font apparaître des différences caracté­ristiques entre les AH et les AF.

3.1. ACIDES HUMIQUES (fig. 1)

3.1.1. Transmission

Les vues à deux dimensions font apparaître les AH comme des "lames" opaques, à bords plus ou moins déchiquetés. Les dimensions des "lames" présentent un large éventail de valeurs, suivant Ie degré de broyage ou de désagrégation par les ultrasons.

3.1.2. Balayage

Les vues à trois dimensions fournies par Ie microscope à balayage montrent des images diverses de lames, plus ou moins contournées, parfois soudées entre elles. Les dimensions de ces éléments sont très variables, les bords sont plus ou moins déchiquetés. Les ensembles montrent des proportions variables de vides.

Des structures assez semblables ont été observées pour les AH de sols méditerranéens (Chen et al., 1978) ou de paramos (Escobedo, 1980). Ceci pourrait faire croire à une unité de la structure interne des AH, queUe que soit leur origine. 11 faut, cependant, se garder des con­clusions trop hatives, car on a mainte fois montré que la technique et les modalités de préparation des échantillons influencent fortement leur aspect (Chen & Schnitzer, 1976; Nguyen Kha, 1979).

277

278

3.2. ACIDES FULVIQUES (fig. 2)

3.2.1. Transmission

Les élérnents figurés sont de dimensions bien inférieures à celles des AH. Sur un fond amorphe ou sub-amorphe, on distingue des particules globuleuses, élémentaires ou plus ou moins agglomérées en amas plus ou moins volumineux, plus ou moins laches. Les dimensions des parti­cules unitair es paraissent assez variables mais, en moyenne, voisines de 300.R. Schilitzer et Kodama (1975) mentionnent des dimensions de 15 à 20 .R.

D'autre part, on observe aussi des particules plus volumineuses, al­longées, évoquant la forme de bactéries et de dimensions moyennes voisines de 1 Jl x 0,3 Jl.

3.2.2. Balayage

Particules globuleuses élémentaires et agglomérées s'observent éga­lement très aisément sur les lames, de même que les particules bactéri­formes dont les dimensions sont confirmées et qui paraissent particu­lièrement abondantes.

Des éléments allongés sont mentionnés par Schnitzer & Kodama (1975) mais ces auteurs n'en donnent pas de représentation. Ils ne sont observés ni par chen et al. (1978) ni par Escobedo (1980).

4. EN GUISE DE CONCLUSION

Nous n'avons présenté ici que les tout es premières observations effectuées à l'occasion d'un travail plus complet portant sur les humus muil à dysmoder.

De la documentation disponible à ce jour, on peut déjà conclure: 1) que les AH et les AF se distinguent nette ment les uns des autres, ne fût-ce que par la taille de leurs éléments unitaires; 2) que les AF paraissent se caractériser par l'abondance d'éléments al­longés, bactériformes, à dimensions de l'ordre de grandeur du micron; 3) que la préparation des échantillons doit se faire selon une technique rigoureusement standardisée, pour permettre la comparaison des objets d'étude.

Chen Y. & Schnitzer M., (1976). Scanning Electron Microscopy of a Humic Acid and of a Fulvic Acid and its Metal and Clay Complexes. Soil Sci. Soc. Amer. J., 40 (5) 682-686.

279

Chen Y., Senesi N. & Schnitzer M., (1978). Chemical and Physical Characteristics of Humic and Fulvic Acids Extracted from Soils of Mediterranean Region. Geoderma, 20 (2) 87-104.

Delecour F., (1975). Note sur la distribution du carbone et de l'azote dans les fractions humiques de quelques sols forestiers. Pédologie, 25 (2) 118-125.

Delecour F. & Prince Agbodjan W., (1975). Etude de la matière organique dans une bio-toposéquence de sols forestiers arden­nais. I. Distribution du carbone et de l'azote dans les fractions humiques. Bull. Rech. Agron. Gembloux, 10 (2) 135-150.

Escobedo J., (1980). Les Sols des Paramos. Etude pédogénétique dans les Hautes Andes du Pérou sep­tentrionnal. Thèse de Doct., Fac. Sci. Agron. Gembloux, 402 p.

Gascho G. J. & Stevenson F. J., (1968). An Improved Method for Extracting Organic Matter from SoU. Soil Sci. Soc. Amer. Proc., 32 (1) 117-119.

Nguyen Kha, (1979). Essai de caractérisation, par microscopie électronique, de la microstructure et du degré d'agrégation des acides humiques extraits de plusieurs types de sols. Collo Intern. Migrations organo-minérales, C.N.R.S., Nancy, 1979 (à paraître).

Prince Agbodjan W. & Delecour F., (1975). Etude de la matière organique dans une bio-toposéqUence de sols forestiers arden­nais. 11. Caractérisation physico-chimique des fractions humiques. Bull.Rech. Agron. Gembloux, 10 (3) 275-290.

Schnitzer M. & Kodama M., (1975). An Electron Microscopic Examination of Fulvic Acid. Geoderma, 13 (4) 279-287.

Résumé

Acides humiques et fulviques d'un sol brun acide se distinguent nettement par la taille et la forme de leurs éléments.

Organisch materiaal onder de elektronenmikroskoop

Samenvatting

Humiene en fulviene zuren van een zure bruine bodem verschillen duidelijk door de grootte en de vorm van hun elementen.

280

Organic matter under the electron microscope

Summary

Humic and fulvic acids of an acid brown soil are different as far as the sÏze and shape of their elements are concerned.

281

PEDOLOGIE, XXX, 2, p. 283-304, 7 fig., 9 tab., 1 app., Gent, 1980.

MINERALOGY OF A SOIL SEQUENCE FORMED UNDER THE INFLUENCE OF SALINE AND ALKALINE CONDITIONS IN THE SARVES1'AN BASIN (IRAN)

A.ABTAHI H. ESWARAN

G. STOOPS C. SYS

1.INTRODUCTION

Studies on soil mineralogy frequently emphasize the day composi­tion with some additional infonnation on the sand and silt fraction, whereas the soluble fraction of the soils, induding Ie ss soluble minerals such as gypsum and calcite, is removed. These latter minerals, especially in some of the Aridisols, may be most important in tenns of absolute quantity and their pedogenetical and fertility implications. Consequently, in addition to the mineralogy of the day, silt and sand fraction, the nature of the other minerals is also examined in the present study.

In the sequence of soils under consideration, both the age and the electrolyte composition are varying. In addition to the mineralogical characterisation, a subsidiary objective is to ob serve the mineralogical variation in relation to these parameters.

Hormites - palygorskite and sepiolite - are alumino-silicate minerals frequendy reported in many Aridisols, in association with smectites and micas (Al Rawi et al., Altaie et al., 1969; Al Rawi et al, 1969; Abtahi, 1977). Many workers have speculated on the origin of palygorskite in soils and evidences for neoformation of this mineral in soils have been provided. In the present study the question will be reexamined with respect to the sequence of soils of the Sarvestan Basin.

Abtahi A. - Soils Dept., Agricultural College, Shiraz University, Shiraz, Iran. Eswaran H., Stoops G., C. Sys - Geological Institute, State University Ghent, Krijgslaan 271, 9000 Ghent, Belgium.

283

Table 1

Classifieation, physiographie position and some analytical data of the promes.

Prof. classifiea tion Physiographie position Depth EC pH CaC03 no.

95 96 15 86

503 19

of mmhos/ H20 % ground- em water in m

Aquollie Salorthid lowland 0-0.5 90-120 8.0 35-43 Aquollie Salorthid " 1 12-74 7.7-8 47-57 Salie Gypsiorthid alluvial plain 2-3 8-110 7.7-8.5 22,5-43 Gypsie Salorthid " " 1.5-2 60-90 8.0-8.3 41-46 Natrie Cam borthid piedmont alluvial plain ~3m 14-21 7.7-8.6 56-58 Calcie Haploxeralf " " " < lOm 0.5-5 7.9-8.2 44-47

2. MATER lAL AND METHODS

The geomorphic and physico-chemical properties of the studied profiles have been described previously (Abtahi et al., 1979). The six profiles discussed here are the lower part of a toposequence, covering the piedmont alluvial plains and the lowlands of the Sarvestan Basin (South-east of Shiraz, Iran). Salinity and alkalinity of the groundwater, and its influence on the soil properties, strongly increase towards the lower members of the sequence.

In table 1 the dassification (according to USDA-system), the physiographic position and some other characteristics of the profiles are summarized. All profiles are formed in fine grained (dayey to silty), calcite rich sediments. They have a relatively high CEC and the soil solution is also rich in electrolytes. Sodium and chloride dominate the cationic and anionic composition of the saturation extract with small amounts of magnesium and potassium and sulphates, carbonates and bicarbonates. In the lowland soils, salt crusts are present.

Clay, silt and sand are separated from each horizon of the profIle. The soils are leached with water to remove any gypsum and soluble salts and the calcium carbonate is removed by treating the soil with IN sodium acetate solution buffered at pH 4.5. A peroxide treatment is applied to destroy organic matter and then the day is fractionated by successive sedimentation. A fifty micron sieve is employed to separate the silt from the sand.

The pretreatments employed are bound to destroy some minerals especially sepiolites. Consequently, water dispersable day is separated for at least one horizon per profile. In addition, the whole soil is ground to a fine powder and this is also subject to detailed analysis.

284

X-ray diffraction (XRD) is perforrned on oriented samples of all the dayfractions and random oriented powders of the silt fractions, some sandfraction and the powdered soil. Selected days are also ob­served with the transmission electron microscope (TEM); the scanning electron microscope (SEM) is used on soil fracture surfaces when necessary. The days are also analysed with differential thermal analysis (DTA) and thermogravimetry (TG). Cation exchange capacity (CEC) of the days and silts is performed using lH NH40Ac at pH 7. The sand is separated into the light and heavy fractions using bromo­form of S.G. 2.85. Total elemental analysis (TEA) of the day is made by a HF dissolution for the bases and Ti and a NaOH fusion for Si and Al. All elements are analysed with atomic absorption spectro-photo­metry. An estimate of the amorphous fraction of the day is made with 0.5 N NaOH according to the procedure of Hashimoto & Jackson (1960). Free iron is determined by the citrate-dithionite-method (Mehra and Jackson, 1960).

A semi-quantitative estimate of the day composition is made em­ploying the results of all the analysis performed. Palygorskites are estimated by using the point count techniques on TEM micrographe developed by Eswaran & Barzanji (1974). The remaining estimates are made according to the allocation procedure suggested by Barshad (1965). The validity of such estimates is checked by comparing the measured CEC of the day to the calculated CEe, the lat ter based on the average CEC values of the different days as reported by Weaver &

Pollard (1973). Smectites are considered to have a CEC of 100, paly­gorskite is 15, chlorite and illite 30 and vermiculite has 150 m. eq. per 100 g day. As shown later, the correspondence of the calculated and measured amounts gives confidence to the estimates.

3. RESULTS

3.1. Powdered soil

Prior to a discussion of the mineralogy of the different partide size dasses, the general com position of the soils is given in table 2. This table presents the results of the XRD analysis of the total ground soil and as the mineralogy of the non-soluble material is presented later, only the salts are indicated. Strong peaks for halite are present in all samples except in profile 19. Other horizons in this profIle may have same halite. Calcite is omnipresent in all soils and in very high amounts. No peaks for gypsum could be discerned in the sample of profile 19 and this may be because it is present in small amounts. Good peaks for gypsum are present in the soils of the alluvial plain.

285

Table 2

XRD analysis of the ground soil material. Only salts are indicated (crosses indicate relative abundanee)

ProfIle Horizon Halite Carnallite Gypsum Calcite Celestite No.

95 Csa,2 xxx x x xxx 96 Csa, 2 xxx x xxx 15 Ces, 1 xx xxx xxx x 86 Ces, 1 xx xx xxx x

503 B22 x x xxx 19 B2t (x) xxx

Weak peaks for celestite are present in the latter soils and weak peaks for carnallite are only present in profile 95.

In the lowland soils, salt crusts are present and both these and salt accumulations in salic horizons were studied in detail by Eswaran et al. (1979). This study showed that halite is the most dominant soluble salt in the crust; small amounts of carnallite (KMgCl3·6H20) are also present. Although the saturation extract contains other anions and cations capable of combination and crystallization as salts, these we re not detected in the study mentioned as they are perhaps present in very small amounts.

3.2. Analysis of the sand

About 60 to 80 % of the heavy fraction of the sand is composed of opaques. Epidote, hornblende and garnet dominate the transparen t heavy minerals with about 30, 20 and 10 % respectively. The other heavy minerals present in smaller and variable amounts, include tourmaline, zircon, andalusite, zoisite and augite. The mineralogical association is not very indicative of the mineralogical province but does seems to suggest a metamorphic origin for the source material

Potash feldspars and plagioclases - 30 and 40 % respectively -dominate the light fraction and quartz forms only about 30 %. Small amounts of muscovite are also present. The high amounts of feldspars indicate the general. youth of the material. Although zeolites have been reported in similar soils, analysis of the total soil or the sand and silt gave no evidence of their presence.

3.3. Analysis of the silt

Analysis of the silt fraction by XRD (fig. 1) is presented in table 3.

286

Profiles

95 C2.Sa

Profile 15 Csa,3

3.35

3.2

32 I 3 55

335 325

l 3 55

15

101

426 10.2

72

145

Profile ~!l wat~er oriented

5038 2,2 . \ ~26 10

/, L J1 li! 7 2

Profile ;J ~ 3.55 j 14.5 1982t,2 J)' 6.45 8 5

2.82 37 4.1 5 475 ~

Water oriented

Fig. 1

X Ray diffractions of silt.

335

I

32 43 10'

3 251 3 55 VJJv2 15 J ï'~ I ' ~, .

Quartz is the dominant mineral · in all the soils. Feldspars show a variabie distribution and seem to be more abundant in the soils of the alluvial plains. Micas and chlorite are also present in all soils though the peaks for the latter are better expressed in the lowland soils. The 14 X peak in profile 95 shifts partially to 18 .R indicating a smectite. It is uncertain if this is siltsized or if it is merely an aggregate of day sized minerals. The peak for palygorskite overlaps with that for the micas and sa the presence of the farmer is confirmed by the 6.45 .R peak. There is an increasing development of the 6.4 5 .R peak proceed-

287

Table 3

Semi-quantitative estimates of the minerals in the silt fraetion (xxxx: abundant; xxx: dominant; xx : moderate; x : few; - : occasional)

Physiography Profile Horizon Quartz Feldspars Chlorite Mica Smeetite Palygorskite No.

Lowland 95 Csa, 1 xxxx xxx x xx x -Csa, 2 xx xxx xx xx x -

Csa, 3 xxxx xxx x x x -Csa, 4 xxxx xxx x xx x -

96 Csa, 1 xxxx xx x x - -Csa, 3 xxxx xx x x - -

Allu vi al plain 86 Al xxx x xxxx x x - -Csa, 1 xxxx xxxx x xx - -Csa, 2 xxxx xxx x x x - -Csa, 3 xxx x xxxx x xx - x Csa, 4 xxxx xxxx x xx - x Csa, 5 xxxx xxxx x x - x

15 Al xxxx xxxx x xx - -Csa, 3 xxxx xxxx x xx - x

Piedmont 503 Ap xxxx xx x x - xx alluvial plain B22 xxxx xx x x - xx

Ces xxxx xxx x x - xx 19 A2 xxxx xxx x x - xx

B2t xxxx xxx x x - xx HCes xxxx xx x x - xx

ing to the better drained soils; the best expressed peaks being in profile 19. The variabie distribution of the felspar may be due to depositional conditions. The secondary minerals, however, indicate a preponderance of smectites in the poody drained members with palygorskite in the well drained soils. This relationship is better expressed in the day fraction.

3.4. Analysis of the day

As the results of genetic processes are best revealed in the composi­tion of the colloid fraction, this is subject to a large number of analyses. Figs. 2 and 3 give the X-ray diffractograms and DT A curves of selected days. Based on these, estimates of the different compo­nents are made and presented in table 4. Estimates of this kind are always questionable but are necessary to make pedo-genetic interpre­tations. To check the validity of the calculations, CEC is measured on the day and the values obtained are compared with the calculated

288

N 00 \.0

'" Profile 95,C,sa2 ~'v/

J~'J" IOp 1 I

P"fiI. ";,;'''3 ! I" '"

~~JJ Profile 5t.3,82 ,2

'" ~

'V Mg++

Fig. 2

J" ","~ 10

"

/

~ JSS ~ tA IJ ~~UVr

fJ' I

~/~/

3 .. :-

~' J\;J I I.' JSS

SOl 7] .

L7') A; -.IJ

Mg++ .0\

'0'

~; hlj~ .J'~", J n

;. J;q 5 ,,'O;~ '1 / -/~{'-J

,,' i\~ I JJ' ,/~ .. , '"

I '" / SI" .

~ 45 " "

K+ K+5500C

X Ray diffraction of total day in the sequence developed under influence of saline groundwater

Prof.95

890 465 506

Prof. 15

461 543 516

Prof . 503

908

163

Prof. 19

517 121 473 554

Fig. 3

DTA diagrarns of total clays; profiles 95 - 15 - 503 - 19

sum of the values for each component. The comparison is presented in table 5 and the agreement is excellent.

The estimate in table 4, indicates a progressive increase of palygor­skite with better drainage conditions. Maximum amounts of palygor­skite are present in the steppified solonetz (Calcic Haploxeralf). Smectite on the other hand shows a reverse trend with the maximum amount in the lowland solonchak (Aquollic Salorthid). The other minerals do not change in the sequence The resul ts of the total elemental analysis of the days fr om which same of the estimates are made are given in the appendix.

The free iron content of the day is given in table 6. There is no apparent trend in the amounts perhaps suggesting that weathering resulting in the liberation of iron is not an important process. The NaOH extraction (Hashimoto & Jackson, 1960) has been used to esti­mate the amorphous alumino-silicates in volcanic ash soils. In the soils

290

Table 4

Semi-quantitative estimates of the minerals in the total day fraetion. Amounts are expressed as tenths of total day. The remainder eonsists mainly of quartz and sm all amoun ts of vermieulite

Proille No. Horizon Palygorskite Smeetite Chlorite Illite

95 Csa,l 2 5 0,5 2 Csa,2 2 5,5 0,5 2 Csa,3 2,5 4,5 0,5 2 Csa,4 2 4,5 1 2

96 Csa,l 2,5 3,5 1 2 Csa,2 2,5 4 1 2

86 Al 3,5 2,5 1 2,5 Csa,l 3,5 3 1 2,5 Csa,3 3,5 3 1 2 Csa, 4 4 2,5 1 2,5 Csa,5 3,5 2,5 1 2,5

15 Al 3 3,5 1 2,5 Csa,3 4,5 2 1 2,5

503 Ap 3 3,5 1,5 2 B22 3 3,5 1 2 Ces 3 3 1,5 2

19 A2 5,5 1 0,5 2,5 B2t 5,5 1,5 0,5 2,5 IICes 4 2,5 1 2,5

under study, some dissolution of the alumino-silicate minerals is ex­pected and so the technique is only used to determine the amount of silica and alumina that can be extracted. The relative values in the different days are more significant than the absolute values. Very high amounts of silica with an associated high Si02/ Al20 3 molar ratio are obtained in the wetter soils. This may be due to the presence of amorphous components or could be an indication that some of the alumino-silicate minerals are poorly crystalline and are easily soluble in the NaOH.

Fig. 4 shows the TEM micrographs of the tot al day. The fibrous mineral is palygorskite and the apparent increase in the weU drained prof tie is evident. The other minerals are indicated on the micrographs.

Several studies indicate a preferential concentration of days in different sub-fractions. In order to investigate this, the day is fraction­ated into three fractions by super-centrifugation and XRD performed on the fractions. Table 7, gives the data for the size analysis of selected days. Very fine day « 0.08 Jlm) forms about 25 % in all the profiles except in profile 19 where it reaches about 50 %. There is a

291

Table 5

Comparison between measured and ealeulated CEC of the days

Profile no. Horizon Measured t Calculated CEC m. eq./lOO g. day)

95 Csa,1 62.4 62 Csa,2 66.4 65 Csa,3 57.6 59 Csa,4 55.6 59

96 Csa,1 48.8 51 Csa,3 48.8 53

86 Al 43.5 43 Csa,1 49.5 46 Csa, 2 43.5 43 Csa,3 46.2 46 Csa, 4 37.2 40 Csa, 5 43.2 45

503 Ap 44.0 47 B22 44.0 50 Ces 44.0 46

15 Al 46.8 49 Csa, 3 36.8 36

19 A2 34.2 30 B2t 34.2 33 HCes 42.8 43

progressive decrease in the coarse fraction (> 0.2 Jlm) with of course an increase in the < 0.2 Jlm in the sequence.

XRD of the coarse (> 0.08 Jlm) and fine day are presented in table 8 and fig. 5. Very characteristically, palygorskite is present only in the fine fraction. TEM analysis, not presented here but available in Abtahi (1974), clearly confirms this. The reason for this is that the palygorskite fibres, because of their brittle nature break down during the fractionation procedure and accumulate in the fine fraction. The micaceous minerals and quartz accumulate preferably in the coarse fraction. The occurrence of micas as large flakes (TEM), indicates that pedogenesis has not comminuted them. Quartz, on the other hand, is considered to go into extinction when it attains a size smaller than 0.08 Jlm (Jackson, 1969). In these soils, this has probably not happen­ed and the absence of quartz in the fine day is probably attributed to the fact that breakdown of quartz has not yet taken place. Smectite concentrates in the fine day though this is not very evident in table 8.

292

Table 6

Citrate-dithionite-bicarbonate extraetabie iron and NaOH extraetabie silica and alumina in the day fraetion

Physiography ProfIle No. Horizon CDB NaOH Extraetabie (%) Fe203 % Si02 A1203 molar ratio's

Lowland 95 Csa, 1 4.1 10.0 1.5 11.32 Csa, 2 4.2 13.2 1.4 15.89 Csa, 3 4.4 10.5 1.7 10.48 Csa, 4 5.2 6.7 1.6 7.10

96 Csa, 1 3.5 4.6 1.0 7.77 Csa, 3 3.6 4.8 1.3 6.25

Alluvial plain 15 Al 3.6 6.1 1.6 6.42 Csa, 3 3.5 4.5 1.5 5.41

86 Al 4.0 5.8 1.8 5.41 Csa, 1 4.0 5.0 1.7 4.90 Csa, 2 4.3 4.9 1.5. 5.58 Csa, 3 4.6 5.0 1.5 5.58 Csa,4 3.9 4.5 1.4 5.41 esa, 5 4.2 5.4 1.6 5.75

Piedmont 503 Ap 3.8 3.9 2.0 3.38 Alluvial plain B22 4.0 3.8 2.2 2.87

Ces 4.0 3.7 1.8 3.55 19 A2 4.0 5.2 1.6 5.58

B2t 3.9 5.3 1.4 6.42 nCes 4.2 5.7 1.5 6.42

Table 7

Percentage of various sub-fractions of the day in the surfaee horizons

Profile No. Horizon 2-0.2 Jlm 0.2-0.08 Jlm < 0.08 Jlm < 0.2 Jlm

95 Csa, 2 57.3 19.7 23.0 42.7 96 Csa, 3 56.5 18.4 25.1 43.6 86 Csa, 3 36.4 25.4 38.2 63.8

503 B22 66.1 13.2 20.7 33.9 19 B2t 23.1 26.6 50.3 76.9

No sepiolites or zeolites were detected in any of the analyses above. The reason for this is because the pretreatments, especially the acidic extraction for the removal of carbonates, would destroy these minerals (Van Den Heuvel. 1966). In order to test for theire presence, water dispersible day from one horizon in each profile is analysed with XRD. A weak peak at 12.5 R in the days of the lowland soils indicates

293

Fig. 4

TEM micrographs of the tota! day in profUe 96 (a), 503 (b), 15 (c) and profUe 19 (d). Magniflcation x 27,000. k : kaolinte, p : palygorskite, m : mica, s : smec­tite.

the presence of sepiolite. DT A analysis confirms the presence of small amounts of this mineral. No sepiolite could be identified in any of the other sam pIes.

294

tv \0 111

JJ5

JJ5 I

Coarse (0.2 - 2 ~)

lOl 145 IU'

Ut 15

lu7

r~ "5

324 Fine(0 . 08~) I

Mg++ Mg++ + GI.

Fig. 5

X Ray diffraction of fine and coarse day of a haploxeralf (ProHle 19)

102

335 I I 33S

11 I~ 101

!

)~ ,,,,0)'" ~ 5 .

n

K+ K + 550°C

Table 8

XRD estimates of the sub-fractions of the day. F = fine day « 0.08 J.lm) and C = coarse day (2-0.08 J.lm). Crosses indicate relative dominanee

PromeNo. Horizon Size Palygorskite Smectite Chlorite Illite Quartz

96 Csa, 3 F xxx xxxx - - -

C - xxx xx xx x 86 Al F xxxx xxx - x -

C - xxx - x -

503 B22 F xxx xxxx - x -

C - xxx xxx xxx x 19 A2 F xxxx xx - - -

C - xx xx xx x B2t F xxxx xx - - -

C - xx xx xxx x IICcs F xxxx xxxx - - -

C - xxxx xx xxxx x

4. DISCUSSION

The mineralogical composition of the day shows a distinct evolution­ary trend. In fig. 6, the mineralogical composition of the day is presented in a tdangular diagram with palygorskite, smectite and the micaceous minerals forming the three apices. The evolutionary trend is very evident with the days proceeding from a smectitic type in the lowlands to a palygorskitic type in the weIl drained soils. It is to he noted that sepiolites were detected in the lowland days hu t not in the other mem hers of the toposequence.

As mentioned already in the introduction, many workers have speculated on the origin of palygorskite in soils. Authigenic occurrence from soil solution of the hormites has been postulated hy Millot (1970), Millot et al. (1977) and McLean et al. (1972). The work of Parry et al. "(1968) and Keith (1972) concur with these ohservations and they believe that these minerals only form in a highly saline and alkaline environment. Further evidences for the neoformation of palygorskites are provided hy S'inger & Norrish (1974). Yaalon &

Wieder (1976) and Eswaran & Barzanji (1974). Employing scanning electron microscopy, the latter showed a network of palygorskite coating gypsum grains; as micromorphological evidence (Barzanji & Stoops, 1974) indicated that the gypsum is a neoformation in these soils, they concluded that the hormite is also a neoformation. Only recently, evidences to indicate that the hormite minerals could form

296

100 I PAlYGORSKi TE I

IC IC

100

I SMECTiTE I

Fig. 6

Trend in mineral evolution in the soils of the Sarvestan basin.

IC - Piedmont alluvial plain

®- Alluvial plain

Á- low land

100

I CHLORITE • ilLiTE I

by the alteration of primary alumino-silicate minerals has been presented by Millot et al. (1977) and Ruellan et al. (1978).

In the present study, palygorskite content is low in highly saline soils and increases with a decrease in salinity. This clearly indicates· the role of the environment in the genesis of this mineral. Table 9, gives the percentage Mg in the groundwater sampled at different points along the sequence, and shows the decrease in Mg content with increas­ing elevation. The other element necessary for the formation of the honnites is silica and the high pH of these soils ensures a sufficient supply of soluble silica.

To further establish the fact that some of the palygorskite is due to neofonnation (it is always possible that the sediment has some honnites) the surfaces of gypsum grains are examined at high magnification. Fig. 7, shows some SEM micrographs of gypsum crystals in a pore in the B2T horizon of profile 15. The high magnification micrographs (fig. 7b, c) clearly show the network of palygorskite on the gypsum grains. The gypsum crystal is undergoing dissolution as evidenced by the etched surfaces. The irregular distribution of the

297

N \0 00

Fig. 7 (a) (b) (c)

Scanning electron micrographs of the gypsum crystals in prom 15 and high magnification observations of the surfaces of gypsum show­ing the coating with palygorskite. (a) x 50, (b) x 5,000, (c) x 10,000.

Table 9

Variation ofMg content of the groundwater at different points along the sequen­ce

Physiography Elevation above lake Percentage Mg of total level (m) cations

Alluvial colluvial plains 200 49 Piedmond alluvial plain 85 41

50 37 30 37

Alluvial plain 5 13 Lowland 1 12

palygorskite (unlike in the micrographs presented hy Eswaran & Bar­zanji, 1974), dearly i~dicates that it is a coating and not simply a surface feature of gypsum.

The environment is also conducive to formation of smectite. Similar coatings of smectite on secondary calcite also point to their neoforma­tion. The preponderance of smectite in the lowland soils, with paly­gorskite in the well drained soils is similar to the sequence studied hy Slansky (cited hy Millot, 1970). Under similar conditions, Parry & Reeves (1968) explained the formation of smectite hy transformation of illite. Burnet et al. (1972) evoked a similar hypothesis for some soils of Iran. There is no evidence emanating from the present study to support these condusions though we do not wish to discount it. How­ever, the estimates of the micaceous minerals in the day do not show any significant changes to support the hypothesis that these are heing transformed to smectite. We prefer to explain the presence of smectite to a neosynthesis fr om soil solution just as in the case of the hormites. The environmental conditions are favourahle and the cations are avail­ahle for neosynthesis.

BIBLIOGRAPHY

AbtahiA., (1974). Contribution to the knowledge of the soils of the Shiraz area (Iran). Ph. D. Thesis, Univ. Gent, Belgium. Mimeo. 314 pp.

Abtahi A., (1977). Effect of a saline and alkaline groundwater on soil genesis in semi-arid Southern Iran. Soil Sci. Soc. Amer. ].41 : 583-587.

299

Abtahi A., Sys c., Stoops G. & Eswaran H., (1979). Soil forrning processes under the influence of saline and alkaline groundwater in the Sarvestan Basin, Iran. Pedologie, 29 : 325-357.

Al Rawi G. H., Sys C. & Laruelle J., (1968). Pedogenetic evolution of the soils of the Mesopotamian Flood Plain. Pedologie, 18 : 63-109.

Al Rawi A. G., Jackson M. L. & Hole F. D., (1969). Mineralogy of some arid and semi-arid land soils of Iraq. Soil Sci. 107 : 480-486.

Al Taie F. H., Sys C. & Stoops G., (1969). Soil groups of Iraq. Their classification and characterization. Pedologie, 19 : 65-103.

Barshad 1., (1965). Thermal analysis techniques for mineral identification and mineralogical com~ position. In : (C. A. Black, Ed.). Methods of Soil Analysis. Part I. Am. Soc. Agron. 9 : 699-742.

Barzanji A. G. & Stoops G., (1974). Fabric and mineralogy of gypsum accumulations in some soils of Iraq. Proc. 10th Int. Congr. Soil Sci. Moscow, VII : 271-277.

Burnett A. D., Fookes P. G. & Robertson R. H. S., (1972). An engineering soil at Kermanshah, Zagros mountains, Iran. Clay minerals, 9 : 329-343. .

Eswaran H. & Barzanji A. F., (1974). Evidence for the neoforrnation of attapulgite in some soils of Iraq. Proc. 10th Int. Congr. Soil Sci., Moscow, VII : 154-161.

Eswaran H., Stoops G. & Abtahi A., (1979). Scanning electron microscopy of halite in soils. In Press.

Hashimoto I. & Jackson M. L., (1960). Rapid dissolution of allophane and kaolinite-halloysite af ter dehydration. Clays and clay minerals. 7 : 102-113.

Jackson M. L., (1969). Soil Chemical Analysis - Advanced Course. Pub!. by author. Univ. Wisconsin, USA, 894 pp.

Keith G. P., (1972). A sepiolite rich Playa deposit in southern Nevada. Clays and Clay Minerals 20 : 211-215.

McLean S. A., Allen B. L. & CraigJ. R., (1972). The occurence of sepiolite and attapulgite on the southern high plains. Clays and clay minerals. 20 : 143-149.

Mehra o. P. & Jackson M. L., (1960). Iron Oxide Removal fr om Soils and Clays by a Dithionite-Citrate System buffered with Sodium Bicarbonate. Clays and Clay Minerals, Proceed., 7th. Con! 317-327.

300

Millot G., (1970). Geology of clays. Masson et Cie., Paris, 429 pp.

Millot G., Nahon D., Paquet H., Ruellan A. & Tardy Y., (1977). L'épigénie calcaire des roches silicatées dans les encroutements carbonatés en pays subaride An tiatlas. Maroc. Sci. Geol. Bull. 30 : 129-152.

Parry W. T. & Reeves C. c., (1968 ) : Clay mineralogy of pluviallake sediments, Southern High Plains, Texas. J. Sed. Petrol. 38 : 516-529.

Ruellan A., Nahon D., Paquet H. & Millot G., (1978). Figures d'épigénie par la calcite dans les encroutements calcaires. In : M. Delgado (Ed.) Micromorfologie de Suelos. Proc. 5th Intern. Working Meet­ing SoilMicromorphology; Granada 1051-1065.

Singer A. & Norrish K., (1974). Pedogenie palygorskite occurrence in Australia. Am. Miner. 50 : 508-517.

Vanden Heuvel R. c., (1966). The occurrence of sepiolite and attapulgite in calcareous zone of a soil near Las Cruces. New Mexico. Clays and Clay Minerals Proc. 13 National Conf. USA, 193-207.

Weaver C. E. & Pollard L. D., (1973). The chemistry of clay minerals. Development in Sedimentology. 15 : 213 pp. Elsevier Scient. Publ. Co. Amsterdam.

Yaalon D. H. & Wieder M., (1976). Pedogenic palygorskite in some acid brown (Calciorthid) soils of Israel. Clay Miner. 11 : 73-80.

Summary

The toposequence of six soils employed in this study show variations in the mineralogy of the day fraction with smectites being abundant in the lowland Salorthids; in the Gypsiorthids of the alluvial plains, equal amounts of smectites and hormites are present while in the Camborthids and Haploxeralfs of the piedmont, hormites are the dominant minerals. Other minerals in the clayfraction include chlorite, vermiculite and quartz, and these do not show variations in the sequence.

In all the soils, there is a concentration of the hormites and smectites in the fine day. The concentration of the former is attributed to their brittle nature, as a result of which they fragment and accumulate in the fine day, during fraction­ation. SEM studies indicate that in general the hormite fibres are long (5-20 pm) and their specific occurrences on gypsum indicate their authigenesis.

Halite and traces of carnallite are present in all soils except the Haploxeralf. The other common minerals are calcite and gypsum. Small amounts of celestite are present in the Gypsiorthids. There is a general uniformity in the heavy and

301

light mineral composition of all the soils indicating a uniformity in the parent material.

Mineralogie van een bodem topo-sekwentie gevormd onder invloed van zout- en alkali grondwater in het Sarvestan bekken (Iran)

Samenvatting

De studie van een toposekwentie met zes profielen laat toe de kleimineralogi­sche verscheidenheid in funktie van het reliëf en de stand van het zout- en alkali­rijke grondwater na te gaan. Smectieten domineren in de Salorthids van de laag­vlakte waar zout grondwater tijdelijk aan de oppervlakte staat, de Gypsiorthids van de alluviale vlakte vertonen een kleifractie met nagenoeg gelijke hoeveelhe­den smectiet en hormietj daarentegen domineren de hormieten de kleifractie van de Cam borthids en de Haploxeralfs van het hoger liggende landschap met diepe grondwatertafel. Andere mineralen welke in nagenoeg gelijke hoeveelheden in de kleifractie van alle profielen voorkomen zijn chloriet, vermiculiet en kwarts.

In alle bodems stelt men een aanrijking van hormiet en smectiet in de fijne kleifractie vast. Deze aanrijking is het gevolg van de breekbaarheid van deze mine­ralen die gedurende het scheidingsproces. fragmenteren. Elektronenmikroskopi­sche studies tonen aan dat de horrnietnaalden veelal lang zijn (5-20 J.1m) en tevens wijst hun voorkomen aan de oppervlakte van gipskristallen op hun vorming "in situ".

Haliet en sporen carnaliet zijn in alle profielen aanwezig met uitzondering van de Haploxeralfs. Kleine hoeveelheden celestiet komen voor in de Gypsiorthids. De uniformiteit van de zandfracties wijst op een homogeen moedermateriaal.

La minéralogie d'une topo-séquence de sols formés sous l'influence d'une nappe saline et alcaline dans Ie bassin de Sarvestan (Iran)

Résumté

La toposéquence de six proftls montre une variation de la minéralogie des argi­les avec des smectites qui dominent dans les Salorthids des fonds; les Gypsiorthids des plaines alluviales présentent des quantités équivalentes de smectites et de hormites, tandis que les hormites dom inent la minéralogie des Camborthids et des Haploxeralfs du piedmont. Autres minéraux présents dans la fraction argüeu­se sont : chlorite, vermiculite et quartz, ceux-ci ne présentent pas de variation dans la séquence.

Dans tous les sols on constate une concentration d'hormites et de smectites dans l'argüe fine. Cette concentration est dû à la fragÜité de ces minéraux , qui se fragmentent au cours du processus de fractionnement. Les études au microscope électronique indiquent que les fibres des hormites sont allongés (5-20 pro) et leurs présence spécifique à la surface du gypse indique leurs formation pédogéné­tique.

Halite, et des traces de carnalite sont présents dans tous les proflls à l'exception

302

du Haploxeralf. Des faibles quantités de celestins s'observent dans les Gypsiorthids. On note une uniformité dans la minéralogie des sables indiquant l'homogénéité du matériel parentiel.

303

Vol o ~

Appendix

Total chemical analysis of the day fraction

Profile No. Horizon Si02 A1203 % %

95 Csa,l 54.33 15.43 Csa,2 54.64 13.69 Csa,3 53.87 15.43 Csa,4 53.12 14.99

96 Csa,l 52.12 15.89 Csa,3 54.18 15.90

15 Al 50.91 13.69 Csa,3 53.12 14.47

86 Al 50.91 14.12 Csa,l 51.35 14.29 Csa,2 52.38 13.95 Csa,3 51.64 13.95 Csa,4 50.35 15.69 Csa,5 51.38 16.19

503 Ap 52.21 17.14 B22 54.38 16.29 Ccs 53.47 16.69

19 A2 51.96 13.17 B2t,2 52.68 14.71 HCcs 51.52 14.71

Fe203 MgO CaO % % %

9.12 5.18 0.27 8.92 5.56 0.15 9.52 5.99 0.17

10.01 5.97 0.14 9.73 5.76 0.03 9.73 6.25 0.01 9.52 6.08 0.27 9.12 5.79 0.44

10.08 6.09 0.39 9.80 6.04 0.38

10.08 5.83 0.39 9.52 6.38 0.42 9.80 5.60 0.32 9.87 5.75 0.30 9.80 4.95 0.01 9.80 5.13 0.01

10.08 5.28 0.28 9.80 6.31 0.26 9.80 6.85 0.01 9.87 6.05 0.01

Na20 K20 Ti02 MnO H20+ H20- Total % % % % % %

0.20 2.21 0.98 tr. 8.09 5.15 100.94 0.21 2.14 0.91 tr. 7.94 7.10 101.26 0.20 2.19 0.94 tr. 8.14 5.23 101.68 0.20 2.24 0.96 tr. 8.12 4.56 100.31 0.19 2.00 0.82 tr. 8.69 4.22 99.35 0.20 2.07 0.87 tr. 8.68 3.51 101.41 0.38 2.52 0.89 tr. 9.04 5.17 98.47 0.34 2.41 0.90 tr. 8.56 4.98 100.43 0.23 2.46 0.96 tr. 6.27 5.93 99.44 0.25 2.43 0.87 tr. 8.31 5.93 99.65 0.22 2.25 0.91 tr. 8.11 6.48 100.60 0.25 2.24 0.87 tr. 8.36 5.91 99.54 0.25 2.36 0.96 tr. 8.50 5.50 99.33 0.23 2.32 0.91 tr. 8.33 5.68 100.96 0.21 1.97 1.24 tr. 7.78 3.98 99.29 0.21 1.98 0.99 tr. 7.70 4.42 100.91 0.23 1.97 1.00 tr. 7.94 4.19 101.13 0.25 2.52 0.87 tr. 8.25 4.75 98.15 0.22 2.51 0.82 tr. 8.50 5.50 101.60 0.21 2.54 0.89 tr. 8.25 5.75 100.10

---------------------------------

SOMMAIRE INHOUD

M. Verloo, L. Kiekens & A. Cottenie Distribution patterns of essential and non-essential trace elements in the soil-soil solution system 163

L. Sine & J .-P. Agneessens Modélisation de la migration d'éléments dans les sols IV. Les modèles discontinus 177

H. Bosmans & J. Paenhuys The distribution of heavy metals in the soils of the Kempen 191

F. Delecour Essai de classification pratique des humus 225

J. M. M. Van den Broek & H. W. Van der Marel Properties and origin of sediments of the Meuse river in the Netherlands and Belgium 243

A. Rassel & F. Delecour Matières organiques au microscope électronique 275

A. Abtahi, H. Eswaran, G. Stoops & C. Sys Mineralogy of a soil sequence formed under the influence of saline and alkaline conditions in the Sarvestan Basin (Iran) 283

D/1980/0346/3

305

Offsetdruk VITA, 9750 Zingem

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