Weathering, clay migration and podzolization in a hydromorphic loess soil

Geoderma - Elsevier Publishing Company, Amsterdam Printed in The Netherlands

WEATHERING, CLAY MIGRATION AND PODZOLIZATION IN A HYDROMORPHIC LOESS SOIL J.M.M. VAN DEN BROEK and H.W. VAN DER MAREL Institute for Soil Survey, Wageningen (The Netherlands) (Received January 26, 1968) (Resubmitted August 26, 1968) SUMMARY An intensive study was m a d e of a h y d r o m o r p h i c l o e s s soil, which w a s thought to r e p r e s e n t the i n t e r s e c t i o n of at l e a s t t h r e e m o r e or l e s s s i m u l t a neously o p e r a t i n g soil f o r m i n g p r o c e s s e s . M o r p h o l o g i c a l and m i c r o m o r p h o l o g i c a l studies w e r e made; p h y s i c a l and c h e m i c a l a n a l y s e s w e r e c a r r i e d out in o r d e r to u n d e r s t a n d the soil f o r m i n g p r o c e s s e s of this profile. The studies showed that this soil p o s s e s s e s a combination of c h a r a c t e r i s t i c s of a gley soil, a soil with a t e x t u r a l B horizon and a p o d z o l . The r e s u l t s of these i n v e s t i g a t i o n s c o n f i r m the p r o c e s s e s of i l l i m e r i z a t i o n , cheluviation, podzolization and g l e i z a t i o n as found a l r e a d y by n u m e r o u s i n v e s t i g a t o r s in podzols, podzolic gley s o i l s , gley s o i l s and r e l a t e d s o i l s . The c l a s s i f i c a t i o n of s o i l s , in which a n u m b e r of soil p r o c e s s e s a r e active, is u n s a t i s f a c t o r y , b e c a u s e in the s e v e r a l c l a s s i f i c a t i o n s d i f f e r e n t p r o f i l e c r i t e r i a a r e u s e d and t r e a t e d in a d i f f e r e n t way. INTRODUCTION Well d r a i n e d s o i l s with t e x t u r a l B h o r i z o n s p r e v a i l in the l o e s s a r e a of the southern p a r t of the p r o v i n c e of L i m b u r g (The Netherlands). I m p e r f e c t l y d r a i n e d s o i l s a r e of r a r e o c c u r r e n c e and of l i m i t e d extent. B e s i d e s a t e x t u r a l B horizon, they have c h a r a c t e r i s t i c s of w e t n e s s both in the B and A h o r i z o n s . When these gley phenomena a r e caused b y a p e r i o d i c a l l y high ground w a t e r t a b l e , soil f o r m a t i o n is s i m u l t a n e o u s l y a f f e c t e d by p r o c e s s e s of podzolization, mainly as a consequence of w e a t h e r i n g p r o d u c t s f o r m e d d u r i n g the p e r i o d s of high ground w a t e r level d e s c e n d i n g into the subsoil. The ground w a t e r table g r a d u a l l y l o w e r s a f t e r the wet season. In g l e y e d s o i l s , where w a t e r l o g g i n g is due to an i m p e r m e a b l e s u b s t r a t u m at a shallow depth, t h e s e podzolization phenomena a r e n o r m a l l y lacking. This m u s t be a t t r i b u t e d to the soil w a t e r being h a m p e r e d in i t s descent; f o r in this c a s e , the w e a t h e r i n g components, r e s u l t i n g from t h e wet p e r i o d s , do not sink deep into the subsoil. This p a p e r d e a l s with the c h a r a c t e r i s t i c phenomena o c c u r r i n g in t h e f o r m e r kind of s o i l s . M o r p h o l o g i c a l l y , the two kinds of i m p e r f e c t l y d r a i n e d s o i l s a r e quite s i m i l a r , the gley phenomena and the t e x t u r a l B being t h e dominant m o r p h o l o g i c a l c h a r a c t e r i s t i c s . However, the podzol c h a r a c t e r i s t i c s in t h e s e s o i l s a r e m o r p h o l o g i c a l l y not v e r y well e x p r e s s e d and c a n , f o r the g r e a t e r p a r t , only be d e t e c t e d by c h e m i c a l a n a l y s i s . Geoderma, 2 (1968/1969)

121

The purpose of this thorough investigation was, moreover, to attend to a number of more or less contradictory facts relating to the classification of these soils, which have been describedunder many different names,

FACTORS IN SOIL FORMATION The hydromorphic loess soil investigated in this study originates from the northern b o r d e r of the South Limburg loess belt, where these soils occur in d e p r e s s i o n s in a relatively flat region with a gentle m i c r o relief. In this region, s e v e r a l c u r r e n t s flow, which discharge into the r i v e r Maas. In winter, high water levels in these s t r e a m s and r i v e r s cause high ground water levels in the d e p r e s s i o n s of the interfluvial land. The loess deposits date f r o m the Late-Wtirm glaciation period, some 20,000--30,000 y e a r s ago. Towards the north, the l o e s s - c o v e r gradually wedges out, generally becoming somewhat c o a r s e r in the p r o c e s s , though this may occasionally be due to contamination by the substratum when the latter occurs at little depth. Especially when the clay-content of the loess also drops markedly, the soil formation shifts to podzolization. This podzolization process, however, is morphologically not well e x p r e s s e d in the loess parent material. Together with other s o i l - f o r m i n g p r o c e s s e s , podzolization p r o c e s s e s can be noticed in the lighter textured loess soils. The same holds for low lying places where the relief influences the hydrology of the soils. In winter, ground water here can rise to 40 cm below the s u r f a c e and keep this height for s e v e r a l months. In extremely wet periods with great water discharge of the c u r r e n t s , it may even r e a c h the surface and r e m a i n there for some weeks. In s u m m e r , when the level of the r i v e r s is never high, the ground water is almost 2 m or more below the surface. The factor relief not only effects differences in weathering and soil formation, but also in vegetation and m i c r o c l i m a t e . Nowadays, natural vegetation is a factor of no importance, because practically all the land is under cultivation. Only some of the periodically wet depressions are still wooded, but this vegetation can hardly be considered representative of the original vegetation. The surrounding lands have been cleared and there have also been radical changes in the woodland population. High t r e e s a r e mainly planted, such as birch, oak, alder and in some places, conifers. Gale, blackb e r r y and f e r n s o c c u r frequently. As r e g a r d s climate, this region is humid temperate. Rainfall is r a t h e r equally distributed o v e r the y e a r with an annual mean of about 700 mm. The months f r o m F e b r u a r y till May show a minimum. The annual mean t e m p e r a t u r e is about 10°C and the mean s u m m e r and winter t e m p e r a t u r e s a r e 18°C and I°C, respectively. Normally, the relative humidity is high ( > 70%). After De Martonne (1926), the aridity index is 35, which points to a subhumid climate by the classification of Thornwaite (1933). The climate is not the dominating f a c t o r for the podzolization p r o c e s s e s in these profiles. Since the precipitation outweighs the evaporation, it is to be expected that some water and s o i l - c o m p o u n d s will sink into the soil. However, the mineralogical r i c h n e s s of the loess parent material s e r v e s to r e s i s t podzolization to a g r e a t extent. Where it does occur, it must be ascribed to the combined action of the other f a c t o r s which cause weathering and impoverishment of the loess. 122

Geoderma, 2 (1968/1969}

In soil genesis, the duration of the p r o c e s s e s is an important f a c t o r . There is no difference in age between the loess of the low lying gley s o i l s and the surrounding well drained loess soils. Though the possible d u r a t i o n of a p r o c e s s itself is an important question, the o c c u r r e n c e of s u c c e s s i v e p r o c e s s e s is often more important for the morphology and c h a r a c t e r i s t i c s of the actual soil. This soil profile, in particular, shows evidence of a range of succeeding p r o c e s s e s and it can thus be considered a p o l y g e n e t i c profile, in contrast to the well drained loess soils, which r e s i s t e d c h a n g e s in soil formation much better. It is almost impossible to indicate within the profile the m o r p h o l o g ical c h a r a c t e r i s t i c s that reflect the separate geneses of the P l e i s t o c e n e and of the s e v e r a l Holocene periods. Fossil soil features can be p r e s e r v e d under p r e s e n t - d a y climate conditions, because the effect of the latter is in many c a s e s not s t r o n g enough to obliterate them completely. It was previously established that the formation of the actual t e x t u r a l B horizon of the well drained loess soils in South Limburg s t a r t e d 4,000-6,000 y e a r s ago (Van den Broek, 1959). Nothing, however, is known about the operating p r o c e s s e s at that time in the imperfectly drained s o i l s .

SOIL PROFILES

Morphology A profile of the hydromorphic loess soils in one of the wooded s i t e s has been sampled; its description follows below: AO

0 - 5 cm

A1

5-19 cm

A2g

19-35 cm

Blg

42-75 cm

B2g

42-75 cm

Matted litter layer of badly decomposed leaves on t o p of partly disintegrated leaves and twigsl very dark b r o w n (7.5YR 2/2) to very dark grey (10YR 3/1). Abrupt, w a v y lower boundary. Very dark brown to very dark gray brown (10YR 2 / 2 - 3 / 2 ) silt loam with weak crumb s t r u c t u r e , g r a d u a l l y grading into dark gray brown (10YR 4/2) and gray b r o w n (10YR 5/2) in the lower part. Friable with very n u m e r ous roots. Clear and undulating lower boundary. Light brown gray (10YR-2.5Y 6/2) silt loam with f e w diffuse and small mottles of pale brown (10YR 6/3) to yellowish brown (10YR 5/4) colour. Very friable; soft fine platy structure that breaks to weak c r u m b s o r small weak blocky elements. Many roots among w h i c h a r e also some large ones. Boundary c l e a r and s m o o t h . Light gray (2.5Y 7/2) to pinkish gray (10YR 7/2) t r a n sitional horizon. Slightly platy, very firm. Mottling a s in the preceding horizon; decreasing n u m b e r of r o o t s . Gradual and smooth boundary. White (2.5Y 8/2) to very pale brown (10YR 7/3) silt loam with yellow (10YR 7/6) and reddish yellow (7.5YR 6/8) iron stains, as prominent c o a r s e mottles, in v e r tically streaked white and gray matrix. Sticky; f i r m ,

Geoderma, 2 (1968/1969)

123

B2g

42-75 cm

B3g

75-95 cm

Cg

) 95 cm

m e d i u m to c o a r s e blocky s t r u c t u r e with c l e a r , pale brown to light pale brown (10YR 6 / 3 - 6 / 2 ) coatings on the ped s u r f a c e s . Throughout this horizon, hard, c o a r s e iron c o n c r e t i o n s occur, the highest amount of which is found in the lower part. Only a few l a r g e r o o t s p e n e t r a t e this horizon. Gradual and s m o o t h g r a d i n g into B3g. White (10YR 8/1) to light brown g r a y (2.5Y 6/2) and r e d d i s h yellow (7.5YR 6/8) s i l t loam with content of c o a r s e sand i n c r e a s i n g with depth. Sticky; faint coatings on the m o d e r a t e blocky s t r u c t u r a l e l e m e n t s . Iron conc r e t i o n s in a s m a l l e r amount than in B2g. No roots. L o w e r boundary c l e a r and smooth. Light brown g r a y (2.5Y 6/2) s i l t loam r e s t i n g on and l a m i n a t e d with silty, sandy or g r a v e l l y m a t e r i a l ; many d i s t i n c t , c o a r s e , m o t t l e s of s t r o n g brown (7.5YR 5/6) colour, d e c r e a s i n g in n u m b e r with depth. Iron c o n c r e tions as in f o r e g o i n g horizon, but s o f t e r and d i s a p p e a r i n g with depth.

Of this p r o f i l e , s a m p l e s have been taken f r o m the following c h a r a c teristic horizons: A I : 5-12 cm; A2g: 25-35 cm; B2gl: 50-60 cm; B 2 g 2 : 6 0 - 7 0 cm; B3g: 80-90 cm; Cg: 110-120 cm. F o r c o m p a r i s o n , a d e s c r i p t i o n is given of a well d r a i n e d l o e s s soil with a t e x t u r a l B horizon. This p r o f i l e has been s a m p l e d at a s h o r t d i s t a n c e f r o m the f o r e g o i n g p r o f i l e ; in a s m a l l s t r i p of woodland of l e s s than half a h e c t a r e , which was left among c u l t i v a t e d land. The t r e e s growing t h e r e w e r e planted (poplar, m a p l e and wild a l d e r t r e e s ) . P r a c t i c a l l y no u n d e r growth o c c u r r e d . The land is a l m o s t flat with a d i s t i n c t m i c r o r e l i e f showing d e p r e s s i o n s of 1-3 m below the flat p l a t e a u s or r i d g e s . M o r p h o l o g i c a l l y , the s o i l s in the d e p r e s s i o n s a r e the s a m e as those in the high p a r t s . AO

+1 to 3-0 cm

A1

0-10 cm

A2

10-45 cm

B2t

45-80 cm

D

~ 80 cm

124

L i t t e r l a y e r , f a i r l y well d e c o m p o s e d and mixed with m i n e r a l soil; 1 cm to m a x i m u m 3 cm thick. Very d a r k g r a y (10YR 3/1) v e r y f r i a b l e s i l t loam; very l o o s e , fine c r u m b s t r u c t u r e . Distinct l o w e r boundary to A2. Yellowish brown (10YR 5/4) s i l t loam. F r i a b l e ; weak, fine blocky s t r u c t u r e . V e r y fine p o r e s common. N u m e r ous l a r g e and fine r o o t s . G r a d u a l boundary to B2t. Brown (10YR 5/3) s i l t loam, v e r y dark g r a y brown (10YR 5/3), d a r k g r a y (10YR 4/1) to d a r k brown (7.SYR 4/2) coating on the ped s u r f a c e s and pore walls. M o d e r a t e l y fine, i r r e g u l a r blocky s t r u c t u r e ; slightly hard, f r i a b l e . Very fine p o r e s common. Very few roots. Few y e l l o w i s h r e d s t r e a k s . L o w e r boundary undulating and abrupt. Dark to strong brown (7.5YR 5/6-4/4) coarse sand, laminated with thin clayey layers. Prominent coatings of iron and locally of clay on the individual sand grains.

Geoderma, 2 (1968/1969)

Micromorpho logy 1 Undisturbed samples of the profile were taken in tins for the p r e p aration of thin sections. The p r o c e d u r e d e s c r i b e d by Jongerius and Heintberger (1963) was used in o r d e r to obtain " m a m m o t h - s i z e d " thin sections of 15 x 8 cm. These were of the following depths: 0-15, 15--30, 33-48 and 57-72 cm, respectively. According to the description, the soil horizon boundaries are found in these samples at 5, 19, 35 and 42 cm. The thin sections were studied and d e s c r i b e d under the petrographic m i c r o s c o p e at 50 x 80 magnification. The terminology of organic m a t t e r is after Jongerius and Schelling (1960), that of the m i n e r a l f a b r i c s after Brewer (1964).

Horizon A1 S m a t r i x of mainly colourless skeleton g r a i n s which a r e locally coated with some brown amorphous humus. L a r g e amounts of organic m a t t e r of the moder types. In the upper c e n t i m e t r e s of the horizon, the m o d e r is dark brown and consists, mostly, of g r e a t , highly disintegrated e x c r e m e n t s of m a c r o - a r t h r o p o d s and small faecal pellets of m i c r o arthropods. In both types of e x c r e m e n t s , r e m a i n s of plant tissue a r e still clearly visible (Plate IA). The g r e a t number of fungal hyphae is r e m a r k able; a part of which has been consumed by the fauna and is now found as very small semi-opaque splinters in the e x c r e m e n t s . The condition of the m o d e r and the simultaneous o c c u r r e n c e of the hyphae indicates an unfavourable humification. The typical association of m o d e r and many fungal hyphae points to extreme hydrological conditions, resulting in a qualitatively poorly developed soil fauna. As the disintegration of the large exc r e m e n t s indicates periodic drying out and d i r e c t l y underneath this zone f e a t u r e s of m o i s t u r e excess a r e found, it may be concluded that the upper c e n t i m e t r e s of the horizon are alternately dry and wet. In the lower part of the horizon much yellowish-brown m o d e r (small pellets) is present, which is for the most part m o r e or less disintegrated. This indicates reducing conditions due to m o i s t u r e excess. Scattered r e m nants of roots, most of which are strongly humificated, partly converted into moder. In these zones, many fungal hyphae occur. In particular, at the bottom of the horizon;many wide p o r e s and a g g r e g a t e s up to 5 m m wide occur. There a r e marly nests of nearly bare sand g r a i n s on the one side and small t r a c e s of yellowish white, mostly isotropic argillans and argillaceous papules on the other side. There a r e also some f e r r u g i n o u s pedorelicts (Plate IB,C) in nodules of varying size with soil f a b r i c : S m a t r i x consisting of skeleton grains embedded in r e d to nearly black iron .hydroxides and channel a r g i l l o - f e r r a n s with flecked orientation. Horizon A 2 S m a t r i x consisting of closely packed, a l m o s t b a r e skeleton grains, s c a t t e r e d few yellowish grain cutans. Some wide p o r e s , partly containing r e m n a n t s of r o o t s which a r e moderately humified o r converted into moder. IThis paragraph was written by A. Jongerius of the Soil Survey Institute, Wageningen, The Netherlands. The authors are very much indebted to him for the critical investigation and description of the thin sections.

Geoderma, 2 (1968/1969)

125

The whole horizon is riddled with small cutanic a r e a s and argillaceous papules. They vary from yellowish white to brownish yellow and are g e n erally more or less anisotropic. In some pores, y e l l o w i s h - g r a y a r g i l l a n s are formed which are i n t e r s p e r s e d with very fine ( > 3 ~) dark, sharply bordered bodies of unknown nature. Some nodules occur, identical to the pedorelicts of the A1 horizon. (Plate ID,E).

Horizon Blg. S matrix of closely packed skeleton grains, generally coated with fairly thin, yellowish free grain cutans. Numerous s m a l l e r voids and planes. In a part of the s m a l l e r pores, normal void argillans (anisotropic, even yellowish interspersed with the small dark bodies mentioned before). About a third of the soil m a s s consists of nodules up to 2 cm in width. T h e i r S matrix consists of skeleton grains embedded in dark brown or orange brown ferruginous material, the f o r m e r in most cases being surrounded by a wide zone of the latter. Inside as well as outside the nodules many yellow to orange coloured void argillans and plane argillans. There a r e some scattered f e r r a n s also. At many places gray to orange coloured c u t a n s cover brown ones. The latter have always strong orientation, whereas, the f o r m e r may possess a flecked orientation.

Horizon B2g. The S matrix is of the same type as that of the B l g horizon. However, the free grain cutans are thicker and at many places, the pores are f i l l e d up with anisotropic clay. The whole soil m a s s is riddled with strongly anisotropic argillans and papules, generally of a yellow colour, but p a r t l y also of the speckled type. About half the soil m a s s consists of the nodules mentioned before, up to about 3 cm in width. In this horizon, many compound packing voids, vugs and planes occur. In conclusion, it may be said that the micromorphological investigation of the profile shows c l e a r evidence of clay movement. However, two p h a s e s of clay illuviation a r e distinguishable, viz.: (1) Clay illuviation of a fossil soil formation. Remnants of this clay illuviation are still visible in the shape of the pedorelicts, scattered argillans and clay papules. These clay concentrations vary from reddish to yellowish white, but are always strongly anisotropic. (2) More recent clay illuviation, which has probably been induced by

PLATE I A. Moder, strongly humified faecal pellets of m i c r o a r t h r o p o d s . Note the great number of fungal hyphae. Horizon A1, n o r m a l light, 125 x. B. P a r t of a nodule (pedorelict). In the centre a channel argillan. Horizon A2, n o r m a l light, 125 x. C. Same view as Fig.3, but now under s e m i - c r o s s e d nichols. Note the strong and continuous orientation in the bottom part of the argillan, the flecked orientation in the higher part thereof. D. Orange-brown argillan covered by a greyish yellow one of the speckled type. Horizon A2, light, 360 x . E. Same view as Fig.5, but now under c r o s s e d nichols. The o r a n g e - b r o w n argillan shows strong and continuous orientation, whereas the speckled one has a flecked orientation. Geoderma, 2 (1968/1969)

127

Sorting coefficient

291

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15-

BZg depth (cm)

1.o

varying depths

5'0

0

r 150

I()0

B2gl

Log ,kewness

1

-

2

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. . . . .

x

3

I ...............

•

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IIOO00000

0/,

B2t ...............

C1

0.3

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•

B2g2

// 0200 •0

I

:::

I A2g II I

ooo 0 •

• I/ A1 "~

0"

128

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A1

vorying oepths B

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,

0

I;

3 "

depth (cm)

A21 ""-..,.i A22 50

100

150

Geoderma,

2

(1~68/1969)

2

strongly reducing c i r c u m s t a n c e s : reduction of the iron components in the nodules. The strongly reduced argillans "dissolve", after which the c l a y , originating from these argillans and moving downward in the profile, s e t t l e s again in the form of argillans, mainly of the speckled type, which may possess, a flecked orientation.

Analyses Granulometric analyses The integral c u r v e s (fractions < 80 p by a e r o m e t e r and > 80 ~ s i e v e s ) of the profile samples correspond with those of the normal loess of t h i s region. After the triangle diagram with the textural c l a s s e s of the U.S. Dept. of Agriculture the samples investigated belong to the silt loam class. T h e texture of the B2g horizon shifts slightly to the silty clay loam class because of its higher clay content. Both the A horizons and the B3g and Cg horizons have lower clay contents; the A horizons show clearly a g r e a t e r silt content that the B3g and Cg horizons. F r o m the g r a n u l o m e t r i c d i a g r a m s the log skewness and the sorting coefficient 1 were calculated (Fig. 1). T h e results show that both values are higher for samples from the textural B horizon than from the A or C horizons. Data from horizons of two well drained loess profiles with textural B horizons, which are drawn in F i g . 1 for comparison, show the same phenomenon. In the hydromorphic p r o f i l e this phenomenon is much more accentuated. When compared to the r e s u l t s of samples from other loess soils with textural B horizons, log s k e w n e s s of the B2gl horizon of the hydromorphic soil profile is the highest by f a r . This points to strong eluviation and illuviation of clay sized p a r t i c l e s . F o r the sorting coefficient the data are less pronounced. The frequency c u r v e s of the soil separates show that the sand f r a c t i o n ( 50 ~t) in the B3g and Cg horizons is l a r g e r than in the top soil l a y e r s (Fig.2). The r e v e r s e holds for the 10 to 25 ~ s e p a r a t e s of these horizons. This phenomenon is common when loess overlies (fluviatile) sands. It is cau sed by contamination with this sandy material at the beginning of the l o e s s deposition. With the gradual increase of the loess thickness and the blocking of sand depots by extension of the loess cover, the supply of s a n d g r a i n s in the loess deposits diminished. Basal p a r t s of loess deposits on sands frequently show a transitional zone of loess in which the sand f r a c t i o n i n c r e a s e s with depth, varying in thickness from 10 to 50 cm. 1log skewness = log (Q 1Q3/rnd2); sorting coefficient = k/Q3/Q1 in which Q1, m d and Q 3 are the first quartile, the median and the third quartile i.e. those particle diameters which have 25, 50 and 75% of the distribution smaller than themselves respectively. Fig.l.A. Sorting coefficient (V-'Q3/Q1) and B. log skewness [log (Q1Q3/rnd2)] of s a m p l e s from the horizons of the hydromorphic l o e s s soil and two well d r a i n e d loess soils with textural B horizons and of s o m e other loess s a m p l e s : I = hydromorphic loess profile; 2 and 3 = well drained loess p r o f i l e s with textural B horizons; 4 = miscellaneous s a m p l e s . Geoderma, 2 (1968/1969)

129

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0

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-gOt'O

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-900 -cjo0

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bl 0 ~=~

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bl m -910"0

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-LO0O

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- t, O 0 " O

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Geoderma,

2

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(1968/1969)

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'

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P - f i x a t i o n (fro) o K- fixotion (o/o)

dry method . . . .

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- - -

wet method

0 , CEC (mequiv./100 g)

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8

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Fig.3. Specific surface, humus and nitrogen content, P-fixation, K-fixation, cation exchange capacity (C.E.C.) and exchangeable cations the profile horizons.

of

G e o d e r m a , 2 (1968/1969)

131

Specific surface Specific s u r f a c e of the p r o f i l e s a m p l e s was d e t e r m i n e d by the D y a l H e n d r i c k s method. The values obtained r a n g e f r o m 24 m 2/g in the A2g horizon to 84 m 2 / g in the B2gl horizon (Fig.3). These data c l e a r l y d e m o n s t r a t e the l o s s of fine p a r t i c l e s f r o m the eluvial horizon and t h e i r d e p osition in the B horizon. Specific s u r f a c e of common l o e s s s o i l s with t e x t u r a l B r a n g e s f r o m 20 to 38 m 2 / g in the A l a y e r s and f r o m 30 to 50 m 2 / g in the B h o r i z o n s . This h y d r o m o r p h i c p r o f i l e thus fits in quite well with the g e n e r a l a s p e c t of the l o e s s s o i l s with clay m i g r a t i o n ( l e s s i v a t i o n ) . The high value for the s p e c i f i c s u r f a c e in the B horizon of the gley p r o f i l e is n e v e r t h e l e s s r e m a r k a b l e . The s p e c i f i c s u r f a c e of the s e p a r a t e < 2 p shows v a l u e s f r o m 155 to 200 mg2/g.

Hunzus and nitroge~¢ Humus content of the p r o f i l e s a m p l e s (K2Cr207-H2SO4 method) is highest in the A horizon (Fig.3). A l i t t e r l a y e r c o n s i s t i n g of N - p o 0 r o r g a n i c m a t t e r , about 5 cm thick, o v e r l i e s this horizon. The o c c u r r e n c e of such a c o v e r of badly d e c o m p o s e d o r g a n i c m a t e r i a l is v e r y c h a r a c t e r i s t i c for these kinds of h y d r o m o r p h i c s o i l s , which a r e poor in plant n u t r i e n t s . The s a m e holds true f o r podzol s o i l s u n d e r the Dutch c l i m a t i c conditions, e s p e c i a l l y f o r humus podzols, in which d e c o m p o s i t i o n and m i n e r a l i z a tion of o r g a n i c m a t t e r is insufficient in consequence of low b i o l o g i c a l a c t i v i t y as a r e s u l t of bad c h e m i c a l and p h y s i c a l conditions. A n t i t h e t i c a l l y , in well d r a i n e d l o e s s s o i l s , whether or not with a t e x t u r a l B h o r i z o n but a l w a y s having a h i g h e r b a s e status, a p e r m a n e n t l i t t e r l a y e r is l a c k i n g or only faintly developed. Nitrogen of the h y d r o m o r p h i c soil is highest in the topsoil (Fig.3), the amount d e c r e a s i n g with depth. The h u m u s / N quotient, which has a value of o v e r 40 in the A1 horizon, d e c r e a s e s with depth. The values in the top l a y e r s a r e even twice as high as those of the humic horizon of well d r a i n e d soils.

P-fixation All h o r i z o n s of the profile fix a p p r e c i a b l e a m o u n t s of phosphate (Fig.3). The P - f i x a t i o n values a r e much h i g h e r than those found in well d r a i n e d l o e s s s o i l s , where P - f i x a t i o n s e l d o m e x c e e d s 25%. The r e l a t i v e l y high v a l u e s in the h y d r o m o r p h i c s o i l a r e c a u s e d by a g r e a t amount of a c t i v e F e 2 0 3 and A1203 and in p a r t i c u l a r by the v e r y low pH values.

h -fixatio~z T h e r e is l i t t l e p o t a s s i u m fixation in all h o r i z o n s of the p r o f i l e and l e a s t in the A2g horizon (Fig.3). This l a y e r contains the g r e a t e s t amount of i n e r t q u a r t z , which may be an explanation of the low affinity f o r p o t a s s i u m . K - f i x a t i o n v a l u e s a r e r e l a t i v e l y low when c o m p a r e d to those found in well d r a i n e d l o e s s s o i l s , where K - f i x a t i o n , d e t e r m i n e d by the dry method, can be as high as 40% in top soil h o r i z o n s and even 60% in the t e x t u r a l B h o r i z o n s .

pH and redox coefficient (rH) The pH v a l u e s of all h o r i z o n s of the h y d r o m o r p h i c p r o f i l e a r e v e r y low, even in the l e s s w e a t h e r e d s u b s o i l (Table I). A p p a r e n t l y t h e r e is no a p p r e c i a b l e b u f f e r i n g action of m i n e r a l r e s e r v e s p r e s e n t . In the s a m p l e of 132

Geoderma, 2 (1968/1969)

TABLE I pH-H20 and rH (redox coefficient) of the h y d r o m o r p h i c l o e s s soil and of s o m e o t h e r soils

Horizon designation and depth in cm below surface

Humus (%)

After wetting (2 months) pH rH

After drying (5h at I05°C) pH

rH

Hydromorphic loess soil (Netherlands): A1 5-12 4.29 4.2 A2g 25-35 1.20 4.0 B2gl 50-60 0.45 3.9 B2g2 60-70 0.37 3.9 B3g 80-90 0.18 3.9 Cg 110-120 0.17 4.0

21.6 25.6 27.0 27.1 27.0 27.6

3.9 4.0 4.0 4.0 3.9 4.0

23.6 25.6 26.9 27.1 26.9 27.7

Pseudo-gley soil on loam (DSle, France): Alg surface 3.06 5.7 A2gl ca. 20 1.61 4.5 A2g2 ca. 35 1.22 4.6 B2g ca.140 0.49 5.1

18.7 22.4 23.0 25.3

4.6 4.5 4.5 4.5

25.2 25.7 25.8 25.7

Gray brown podzolic soil on loess (Netherlands): A1 0-10 20.53 4.0 A21 10-25 2.64 4.5 A22 25-45 1.11 4.2 B2tl 45-60 0.61 4.3 B2t2 60-80 0.40 4.3 D 80-90 0.28 4.3 D 90-100 0.50 4.5 D 120-135 0.22 4.8

24.5 26.1 28.0 27.8 27.9 27.6 27.7 28.0

4.0 4.6 4.3 4.4 4.3 4.4 4.6 4.8

25.2 27.1 28.0 27.7 28.2 27.8 27.7 27.9

Marine m u d s (Netherlands): Surface 8.66 Surface 14.64 Surface 15.90 Surface 15.36 Surface 9.75 Surface 10.46 Surface 5.04 Surface 4.03

7.7 7.4 7.0 6.3 7.4 8.1 8.0 7.6

15.1 18.5 19.2 18.1 9.5 16.8 16.2 15.2

7.8 7.7 7.2 5.0 8.3 8.3 8.2 8.2

29.1 26.4 28.5 27.7 28.2 29.2 30.8 28.0

Marine m u d s (Belgium): Surface Surface Surface Surface

10.11 10.81 9.49 9.39

7.2 7.2 7.0 7.0

24.5 24.8 25.6 25.4

7.5 7.3 7.3 7.1

29.1 28.3 26.2 26.1

M a r i n e m u d s ( B r i t i s h Guiana): Surface 1.26 Surface 1.55 Surface 2.30

7.5 7.8 7.2

20.7 22.6 21.8

8.2 8.1 8.1

28.3 27.1 30.6

t h e A1 h o r i z o n of t h i s p r o f i l e , w h i c h c o n t a i n s 4.29% of h u m u s , a s l i g h t l y reducing environment comes into being when the sample is submerged. A d e c r e a s e in r H of t h e s o i l w h e n it i s s u b m e r g e d in w a t e r m a y c o m e a b o u t very quickly, i.e., even within a few hours, when easily reductive organic matter and enough active micro-organisms are present. Marine muds on

G e o d e r m a , 2 (1968/1969)

133

the other hand, may have v e r y low r e d o x c o e f f i c i e n t s , although t h e i r pH values a r e m a r k e d l y h i g h e r ( T a b l e I). Low redox coefficients p r o m o t e leaching of iron (and m a n g a n e s e ) to d e e p e r l a y e r s . At very low rH v a l u e s (about 12) sulfate anions a r e r e d u c e d to H2S (Rivi~re and Vernhet, 1959) and even to f r e e S at rH v a l u e s of about 10 (P. van d e r Sluis, p e r s o n a l c o m m u n i c a t i o n , 1968) Low rH v a l u e s a r e c a u s e d by r e d u c i b l e organic compounds in the soil. Humus content as d e t e r m i n e d b y the K2Cr20-H2SO4 method gives only the amount of e a s i l y o x i d i z a b l e o r g a n i c m a t e r i a l in a c e r t a i n a c i d i c o x i d a t i v e environment. This method i s , t h e r e f o r e , not s u i t a b l e for the e s t i m a t i o n of r e d u c i b l e o r g a n i c compounds. Another f a c t o r influencing o x i d a t i o n - r e d u c t i o n s t a t u s of a soil is the pH. An a l k a l i n e environment d e c r e a s e s H 2 p r e s s u r e in the s o i l s u s p e n s i o n and, t h e r e f o r e , i n c r e a s e s the redox coefficient. High p e r c e n t a g e s of o r g a n i c m a t t e r , t h e r e f o r e , do not always coincide with low r e d o x c o e f f i c i e n t s and c o n v e r s e l y ( s e e f o r e x a m p l e s Table I).

Cation exchange capacity (C.E.C.) and exchangeable cations C.E.C. values of the p r o f i l e a r e lowest in the A2 horizon and highest in the B horizon, e s p e c i a l l y in the B2gl h o r i z o n (Fig.3). The somewhat higher C.E.C. value of the A1 horizon c o m p a r e d to the A2g horizon is mainly c a u s e d by the g r e a t e r humus content of the f o r m e r . The C.E.C. r e l a t e s to the s p e c i f i c s u r f a c e v a l u e s of both the soil a s a whole and its 2 ~ s e p a r a t e (Fig.4). The 2 ~z s e p a r a t e has somewhat h i g h e r C.E.C. v a l u e s p e r unit of s p e c i f i c s u r f a c e in consequence of its r e l a t i v e l y s m a l l e r content of i n e r t (quartz) m a t e r i a l . T h e r e is no s t r i k i n g d i f f e r e n c e in this r e s p e c t between s a m p l e s of the h y d r o m o r p h i c and of common well d r a i n e d loess soils. Exchangeable cations of the gley p r o f i l e h o r i z o n s m a i n l y c o n s i s t of H +, AI(OH)~, A1 (OH) 2+ cations (Fig.3). T h e r e is an i n v e r s e r e l a t i o n between pH and the sum of these c a t i o n s (Fig.5). The A horizons a r e a l m o s t c o m p l e t e l y s a t u r a t e d with t h e s e ions, which is attended with a b a s e s a t u r a t i o n of p r a c t i c a l l y zero. In the s u b s o i l h o r i z o n s the b a s e s a t u r a t i o n is somewhat h i g h e r due to the p r e s e n c e of m e t a l l i c cations, although not s u r p a s s i n g 20%. In c o m p a r i s o n with Fig.4. Cation exchange c a p a c i t y (C.E.C.) and specific s u r f a c e of the p r o f i l e h o r i z o n s and of s o m e o t h e r l o e s s s a m p l e s : 1 = whole fine e a r t h ~ h y d r o m o r p h i c l o e s s . 2 separate ~ 2 p J 3 = whole fine e a r t h 4 s e p a r a t e ~ 2 p .~

well d r a i n e d l o e s s .

5 = v a r i a t i o n as found f o r k a o l i n i t e , i l l i t e , glauconite, s o i l m o n t m o r i l l o n i t e , n o r m a l m o n t m o r i l l o n i t e - a c c o r d i n g to Van d e r M a r e l (1966). Fig. 5. Cation exchange c a p a c i t y (C. E.C.) minus total e x c h a n g e a b l e b a s e s [H + + A1 (OH)~ + A1 (OH) 2+] in % of C.E.C. and the pH of the soil s u s p e n s i o n of the p r o f i l e h o r i z o n s and of s o m e other soil s a m p l e s : 1 = h y d r o m o r p h i c l o e s s p r o f i l e ; 2 = a l l u v i a l s o i l s (Roer, N e t h e r l a n d s ) ; 3 = pseudogley soil (DSle, F r a n c e ) ; 4 = well d r a i n e d l o e s s (Netherlands). 134

Geoderma, 2 (1968/1969)

C.E.C. ( mequiv./1OOg ) •

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X2

60

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J

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B292

xX A1

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ts

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Specific surface

,oo

s'o I

m2/g

2oo

pH 1

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I I I 8-I

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44

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1

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20

0

40

60

80

G e o d e r m a , 2 (1968/1969)

I

100 °/o of C,E~

135

p s e u d o - g l e y p r o f i l e s and m o r e e s p e c i a l l y with well d r a i n e d l o e s s s o i l s , the amount of H +, AI(OH)~ and A1 (OH)2+ in the h y d r o m o r p h i c p r o f i l e is v e r y high, which is connected with the very low pH values. The p r o f i l e has s o m e Ca 2+ and Mg 2+ ions, e s p e c i a l l y in t h e s u b s o i l (Fig.3). Although the m i l l i - e q u i v a l e n t values of these c a t i o n s a r e e x t r e m e l y low, the r e l atively higher Mg 2+ content is r e m a r k a b l e and is r e g a r d e d by s o m e a u t h o r s as a c h a r a c t e r i s t i c of p s e u d o - g l e y p r o f i l e s . A p o s s i b l e e x p l a n a t i o n m a y be found in the difference in e l e c t r o - n e g a t i v i t y of the Mg 2+ and the Ca 2+ ion, v i z . . 1.2 eV and 1.0 eV r e s p e c t i v e l y . The Ca atom is m o r e e a s i l y ionized in s o l u t i o n s and, t h e r e fore, m o r e r e a d i l y l e a c h e d to subsoil. During the w e a t h e r i n g p r o c e s s Mg will r e l a t i v e l y gain on Ca. The amount of exchangeable K + ions is v e r y s m a l l , e s p e c i a l l y in the top layers. In well d r a i n e d l o e s s s o i l s Ca 2+ and to a l e s s e r extent a l s o Mg 2+ a r e the p r e d o m i n a n t cations, w h i l s t b a s e s a t u r a t i o n in the s o i l s is o v e r 80% n o r m a l l y and only o c c a s i o n a l l y in the A horizon as low as 50%.

Total (Bausch) analysis and 25% HCl extraction of the soil The d i f f e r e n c e s w e r e a s c e r t a i n e d between the total a m o u n t of the c o m p o nents found by Bausch a n a l y s i s and the amount e x t r a c t e d by 25% HC1 at 100°C for 1 h (followed by e x t r a c t i o n with NaOH s.g. 1.035 f o r 20 m i n at 55°C to d i s solve SiO2 p r e c i p i t a t e d by the h y d r o c h l o r i c acid). The d i f f e r e n c e s p r o v e d to be g r e a t for K 2 0 , Na20, CaO, TiO2, Mn304 and SiO2 (Fig.6). Evidently the v a r i o u s h o r i z o n s m a i n l y c o n s i s t of a c i d - r e s i s t i n g m a t e r i a l . F o r MgO, P205, A1203 and in p a r t i c u l a r for Fe203 t h e d i f f e r e n c e s b e tween the total amount and the amount d i s s o l v e d by 25% HC1 a r e s m a l l e r , which points to a l a r g e r amount of a c i d - s o l u b l e m a t e r i a l . L o s s of components in the top l a y e r s , e s p e c i a l l y f r o m the A2g horizon, is g r e a t e s t f o r MgO, Mn304, P205, A1203 and in p a r t i c u l a r f o r F e 2 0 3 . P 2 0 5 leaching to the s u b s o i l can be followed to the B2gl and for M n 3 0 4 even to the B2g2 horizon, which points to a g r e a t e r m o b i l i t y of t h e s e two e l e m e n t s c o m p a r e d to MgO, A1203 and F e 2 0 3 . Na20, TiO2 and SiO2 have the s m a l l e s t d i f f e r e n c e s in c o n t e n t between the s e v e r a l h o r i z o n s . K 2 0 and CaO occupy an i n t e r m e d i a t e p o s i t i o n in r e l a t i v e leaching. In many p u b l i c a t i o n s the c h e m i c a l d i s p l a c e m e n t of Fe, A1, and Mn has been t r e a t e d . The conclusion a r r i v e d at is that o r g a n i c m a t t e r of plant or a n i m a l o r i g i n with a c i d i c c a r b o x y l s , phenolic h y d r o x y l s and a m i d e g r o u p s f o r m s soluble F e - , A1- and Mn- compounds of chelate (ring) s t r u c t u r e , which a r e only s l i g h t l y s e n s i t i v e to p r e c i p i t a t i o n . The s t r o n g l y r e d u c i n g e n v i r o n m e n t which p r e v a i l s in the soil solution of the top l i t t e r l a y e r in the wet s e a s o n a l s o p r o m o t e s leaching of F e , A1, Mn and P to d e e p e r l a y e r s . Other f a v o u r a b l e c i r c u m s t a n c e s for d i s p l a c e m e n t of t h e s e e l e m e n t s a r e , v e r y low pH and abundance of w a t e r t i l l late spring. F e , A1, s i l i c i c a c i d and the finer s o i l p a r t i c l e s a r e f l o c c u l e n t at a c e r t a i n depth, which in low lying wet s o i l s is a l s o influenced by the level of the ground w a t e r in s u m m e r . This r e s u l t s f r o m the c o m p o s i t i o n and the r e d o x coefficient of the e n v i r o n m e n t and m i c r o b i o l o g i c a l a c t i v i t y , which a r e d i f f e r e n t f r o m those of the l e a c h e d h o r i z o n s above. I n c r e a s i n g i m p e r m e a b i l i t y of the illuviation zone p r e v e n t s these components f r o m p e n e t r a t ing into the deep subsoil. 136

Geoderma, 2 (1968/1969)

In e x t r e m e c a s e s this p r o c e s s may eventually even lead to the f o r m i n g of a vast i m p e r m e a b l e bank in the subsoil. This may develop into a f r a g i p a n and o c c a s i o n a l l y b e c o m e a few m e t r e s thick over l a r g e a r e a s . Such a compact l a y e r blocks all t r a n s p o r t of soil compounds f r o m the s u r f a c e t o underlying l a y e r s . In the p r o f i l e i n v e s t i g a t e d Fe is e a s i e r moved f r o m the top h o r i z o n s than A1. This is d e m o n s t r a t e d by the S i O 2 / F e 2 0 3 r a t i o , which is h i g h e s t in the A1 and A2g h o r i z o n s , and by the F e 2 0 3 / A 1 2 0 3 r a t i o , which is low in the A2g horizon in c o m p a r i s o n with the B and C h o r i z o n s (Fig.6). T h i s phenomenon of different b e h a v i o u r of the two e l e m e n t s has been s i g n a l i z e d by v a r i o u s i n v e s t i g a t o r s . It is c a u s e d by a d i f f e r e n c e in s o l u b i l i t y and s e n sitivity to r e d u c t i o n and chelation, which has been d i s c u s s e d at g r e a t l e n g t h in l i t e r a t u r e . A d e c r e a s e in SIO2/A1203 r a t i o is found in the illuvial zone. It is d u e to an i n c r e a s e of p a r t i c l e s < 2 p c o n s i s t i n g of A l - c l a y m i n e r a l s in t h e s e l a y e r s , in p a r t i c u l a r in the B2gl horizon, due to leaching f r o m the top l a y e r s ( s e e the d a t a i n Table III f o r the content of p a r t i c l e s < 2 ~ and t h e i r m i n e r a l o g i c a l composition). Consequently in this c a s e an a p p a r e n t l a r g e r mobility of A1 a g a i n s t Fe in the B h o r i z o n s may be p a r t l y a s c r i b e d to a d i s p l a c e m e n t of fine A 1 clay m i n e r a l s . By e x t r a c t i o n of the s o i l s a m p l e s with NaOH s.g. 1.035 for 20 min a t 55°C the data l i s t e d in Table lI w e r e obtained. In this c a s e of weak e x t r a c t i o n , by which mainly a m o r p h o u s gels a n d TABLE II Data obtained by extraction of the soil samples with NaOH s.g. 1.035 for 20 rnin at 55°C. A1

A2g

B2gl

B2g2

B3g

Cg

0.22

0.28

0.43

0.40

0.38

0.30

A1203 (%)

0.49

0.62

0.76

0,52

0.53

0.41

SiO2/A1203 (mol.)

0.76

0.69

0,96

1.31

1.22

1.24

SiO2 (%)

p o o r l y r e s i s t a n t m i n e r a l s a r e d i s s o l v e d , the SIO2/A1203 r a t i o (mol.) i s found to be the h i g h e s t in the B2g2 horizon. A p p a r e n t l y s i l i c i c a c i d is t h e l e a s t s t a b l e in the e n v i r o n m e n t with p e r i o d i c a l fluctuation of the g r o u n d water. It is evident f r o m the Niggli m o l e c u l a r equivalent data (Niggli, 1 9 3 6 ) of the h y d r o m o r p h i c l o e s s s a m p l e s (Fig.7), that the o p e r a t i n g p r o c e s s e s in the p r o f i l e a r e c h a r a c t e r i z e d by the si, alk, fm, and c values. T h e r e i s l e s s e v i d e n c e f o r al and l e a s t for the mg and k values in this r e s p e c t . I n Fig.8 the c h e m i c a l a n a l y s e s of the profile h o r i z o n s a r e r e p r e s e n t e d in a n a t o m i c equivalent d i a g r a m in c o n f o r m i t y with the method of K S h l e r and Raaz (1951). The v a l u e s of the s o i l h o r i z o n s a r e s i t u a t e d in the left p a r t of t h i s d i a g r a m which is the p l a c e of the quartz ( q z ) - r i c h , but f e l d s p a r ( F ) - a n d f e m i c ( f m ) - p o o r r o c k s . The value of the l e a c h e d A2 horizon is n e a r e s t t o the q z - and F - r i c h e r p a r t , those of the B2 (illuviation) h o r i z o n s a r e s o m e Geoderma, 2 (1968/1969)

137

O/o

JO/o

Loss on ignition

1.5

1.0 K20 J o/o 201

0.5 ¸

Totoldissolved 25O/oHCL

0 10 t

/e

O/o

e-- . . . .

No20

•/

0/

,.01o/o".

0.8-

0.4-

0.5

i

T~

0 0

0.3"

°1°

...........

I - ~e . . . .

e-

CoO 0/0 0'041

02-

]

O02J

-

Mn304

~ ~ ' :

.

.

:

~

0.1-

@

•

@

@

II~ . . . . . . . . . . . . . . . . . . . . . . . .

• O/o P205

/ 0.8~ °/° |

MgO

-

_-

0.04-

J

0.4

0

-

0.02-

,,-_.__

0 i

AI 1:

20

I

! ,o

A2g _-

~J - -e .....

• .......

, , , , .

. . . . .

ie°i

B2gl B2g2 2e . . . . . . . . •

8oi

B3g

1oo

•

i,=o Cg

"'''',0

o

~'''~

:=" 2'0 ! ,'o A1

A2g

depth (cm) : ',6o, ;

B2gtB2g2

eo: '~' B3g

i~o

!,~o Cg

Fig.6. The total content of components of the profile horizons (Bausch analyses) and the content of components dissolved by 25 % HC1 at 100°C. l = Bausch analysis; 2 = dissolved by 25% HC1.

138

G e o d e r m a , 2 (1968/1969)

S;O 2 Fe203+AL2 O3

m0t

O/o

~e

Si02

30-

100 205O 10-

0 ........................ 12-

°/o

AL203

tool..

/o

• O-

0.8-

\\ \\

8-

0.4-

\,

//

// //

•

Fe2O:,3 AL203

4-

401mot.

O,

O/o

SiO2 AL203

Fe2 03

12-

=°1 ~=.. . . . . - • . . . . ."

e--e ....

0/

8"

4001 mot

4-

t

I00.

mot.

Fe203

Fe203.FAL203 o .

~ / o- . . . .

0

ii' i

A1

•

.

.

.

.

.

.

.

.

.

.

:

.

.

.

.

.

.

depth

,~ . . . . . . . 60 ;

1

i

A2g

.

: t ,~ o° o ]

•

/

2'o ii

.

,~ol,.o~. ~,o,- ~.,o~+,~,o d

J

50-

0

•

Si02

oot 150-

• ......

80 :

'

i

B2gl B2g2 B3g

,~o ';'id20 i

Cg

0',

.--,--.--T--.-;--':'~---:

~i ~o:,o At

A2g

(cm)

i~ol .~, ,oo !,,o,

B2glB2g2

":--.---.-'e

B3g

Cg

Fig.6 (continued).

*SiO 2 d i s s o l v e d by 25% HC1 at 100°C for 1 h, followed by e x t r a c t i o n with NaOH s . g . 1.035 at 55°C for 20 rain.

G e o d e r m a , 2 (1968/1969)

139

alk

si

1400-

A2g V

fm

mg

C 04-

40-

07-

7AI

x B2gl

•

1200

24 tA2g 30-

TA2g oat 5

oA1 1000

58 ¸

cg + m, • B3g B2g2 06-

0.3oA1

x•2gl Acg

VA2g

20 |B3g Acg

VA2g

B3g Acg

1B3g ACg

oA'l

16-

800

+B2g2 + B2g2

+ B2g~t 4'

eAt XB2gl + B292

IB3gAcg + B 2 g 2 02-

20-

B3g

A2g

0550"

xB2g1

+B2g2

@A2g

X B2gl

oA1

x B2gl g3g

600

12

-

-

10

-

-

0+1

-

-

0.4

-

-

46"

F i g . 7 . N i g g l i (1936) m o l a r e q u i v a l e n t v a l u e s of the p r o f i l e h o r i z o n s . s i = SiO 2. 100/A1203 + ( 2 F e 2 0 3 + F e O + MgO + MnO) + CaO + N a 2 0 + K20; a l k = ( K 2 0 + Na20). 1 0 0 / d i t t o ; f n z = ( 2 F e 2 0 3 + F e O + M g O + M n O ) . 1 0 0 / d i t t o ; c = CaO. 1 0 0 / d i t t o ; a l = A1203. 1 0 0 / d i t t o ; m g = MgO. 1 0 0 / 2 F e 2 0 3 + F e O + MgO +

MnO; k = K 2 0 . 1 0 0 / K 2 0 + N a 2 0 ; F = f e l d s p a r .

what n e a r e r to the f m - r i c h e r and F - p o o r e r zone of the d i a g r a m . A s a r e s u l t of the i l l u v i a t i o n the p o s i t i o n s of the B h o r i z o n s in the d i a g r a m a p p r o a c h t h o s e of the w e l l d r a i n e d l o e s s s o i l s , a l l of w h i c h a r e r i c h e r in m e t a l l i c e l e m e n t s than g l e y s o i l s and p o d z o l s o i l s . Mineralogical

analyses

The m i n e r a l s of the s o i l p r o f i l e s a m p l e s w e r e d e t e r m i n e d in f o u r s e p a r a t e s : '< 2 ~ , 2-16 /z, 16-80 ~ , and > 80 ~. The r e s u l t s a r e g i v e n in T a b l e III and F i g . 9 and 10. S e p a r a t e < 2 ~ . The a m o u n t of q u a r t z i s h i g h e s t in the A1 a n d A 2 g h o r i z o n s . H e r e w e a t h e r i n g and l e a c h i n g a r e m o s t i n t e n s i v e , l e a v i n g b e h i n d the i n s o l u b l e c o m p o n e n t s . K a o l i n i t e w h i c h is a l m o s t a s r e s i s t a n t a s q u a r t z but m u c h s m a l l e r s i z e d on the a v e r a g e , is c o n c e n t r a t e d in the A2g a n d B 2 g l h o r i z o n s . M i c a and i l l i t e , o f f e r i n g l e s s r e s i s t a n c e to w e a t h e r i n g , have t h e l o w e s t a m o u n t in the A1 and A2g h o r i z o n s . In the A1, A2g2 and B2g2 h o r i z o n s i n t e r m e d i a t e m i n e r a l s a r e found,

140

Geoderma, 2 (1968/1969)

which r e s u l t e d from m i c a and illite weathering. The m a x i m u m amount i s found in the B292 horizon. A p p a r e n t l y they a r e c o n c e n t r a t e d here, a f t e r being leached from the upper horizons. I n t e r m e d i a t e , expanded and s w e l l i n g i l l i t e a r e s t a g e s of i n c r e a s e d w e a t h e r i n g of m i c a and illite. C o n s e q u e n t l y , the a b i l i t y of the l a y e r s to c o n t r a c t to 10/~ when t r e a t e d with KC1 d e c r e a s e s in the sequence, w h e r e a s swelling power i n c r e a s e s when t r e a t e d with g l y c e r o l (Fig.9). Expanded illite is found in a l l h o r i z o n s . Swelling illite i s a b s e n t in the A1 and A2g horizons. Small amounts of common ( m a g m a t i c ) chlorite a r e only found in the lower h o r i z o n s where it r e s i s t e d w e a t h e r i n g . Soil chlorite o c c u r s mainly in the A2g horizon but only in s m a l l a m o u n t s . Limonite is found in the lower h o r i z o n s , in c o a r s e iron c o n c r e t i o n s in the zone of the p e r i o d i c a l ground w a t e r as a r e s u l t of e v a p o r a t i o n and p r e c i p i t a t i o n or of m i c r o b i o l o g i c a l activity.

Separate 2-16/~. The top h o r i z o n s , e s p e c i a l l y the A2g horizon, h a v e l a r g e amounts of quartz. The amounts of Na-feldspar (albite) and I~-feldspar ( o r t h o c l a s e , m i k r o -

60

A

E I

40

u..

• 1

20

x 2 qz ~

JA2g

.

2¢ "tB3gB2 2g Cg~e t B2gl ~ ,

.

.

.

.

.

.

.

_10,

• 3 + 4 • 5

~

_ 20 • 6 _40 'E

[ _co ~

J -80

•/BII

J fm

Fig.8. R e p r e s e n t a t i o n of the c h e m i c a l c o m p o s i t i o n of the p r o f i l e h o r i z o n s and of s o m e s a m p l e s f r o m l o e s s and o t h e r s e d i m e n t s in c o n f o r m i t y with the d i a g r a m m a t i c a t o m i c equivalent method of K~Shler-Raaz (1951): 1 = h y d r o m o r p h i c l o e s s profile; 2 = well d r a i n e d l o e s s (Netherlands); 3 = b l a c k r e g u r (India); badob (Sudan); 4 = a l l u v i a l (Netherlands); 5 = w e a t h e r e d s e r p e n t i n e (Italy); 6 = g l a c i a l c l a y s (Finland). Geoderma, 2 (1968/'1969)

141

T A B L E III M i n e r a l o g i c a l c o m p o s i t i o n of t h e p r o f i l e h o r i z o n s in % of e a c h s e p a r a t e a n d of t h e w h o l e fine e a r t h S e p a r a t e s a n d whole sample A1 h o r i z o n : Quartz Feldspar Kaolinite M i c a (+ illite) Sw. and exp. (+ int) illite 1 C h l o r i t e (+ s o i l c h l o r i t e ) T o t a l in % of s e p a r a t e T o t a l in % of whole s a m p l e A2g horizon: Quartz Feldspar Kaolinite M i c a (+ illite) Sw. and exp. (+ int) illite C h l o r i t e (+ s o i l c h l o r i t e ) T o t a l in % of s e p a r a t e T o t a l in % o f whole s a m p l e B2gl horizon: Quartz Feldspar Kaolinite M i c a (+ iltite) Sw. and exp. (+ int) illite Chlorite (+ soil chlorite) Iron concretions

~

80 p

95 2

50.40 7.20

-

1

0.60

100

100

3

T o t a l in % of s e p a r a t e T o t a l in % of whole s a m p l e B3g horizon: Quartz Feldspar Kaolinite M i c a (+ illite) Sw. a n d e x p . (+ int) illite C h l o r i t e (+ s o i l c h l o r i t e ) Limonite Iron concretions T o t a l in % of s e p a r a t e T o t a l in % of whole s a m p l e

9.50 0.20 0.30

2-16 p

84 12 3

1.80

100 tr. 2 tr.

70 12 4 S 6+

60

9.00 tr,

91 8 tr.

-

56.42 4.96

0.62

100 9

87 3

5.22 0.18

4

0.24

6

0.36

83 10 2 4

42.33 5.10 1.02 2.04

1

0.51

tr.

81 7 3 5

48.60 4.20 1.80 3.00

13.92 1.28 0.32 0.48 tr.

5

0.45

4

2.40

33

2.97 100

2.00 0.48 0.48 0.96

79 7 3 7

49.77 4.41 1.89 4.41

3

0.48

4

2.52

10

1.60 100

7.28 0.98 1.12 2.52 0.98 1.12+

5.20 0.26 2.21 1.04+ 3.51+ 0.78+

100.0 84.5 6.5 2.5 1.5+ 3.5+ 1.4+

13 28 2 15 28+ 21+ 6+

99.9

7.28 66.6 0.52 7.2 3.90 6.3 7.28+ 11.3+ 5.46÷ 5.5+ 1.56+ 2,9+ 0.4 26

26 2 12 18+ 32+ 8+ 2

4.42 0.34 2.04 2.06+ 5.44+ 1.36+ 0.34

100.2

64.3 5.8 5.5 9.3+ 6.4+ 5.3+ 0.3 3.0

100

5.06 0.77 0.88 1.98 1.43 0.88

100 63

40 2 17 8+ 27+ 6+

14 46 7 8 18 13 8+

77.8 9.8 1.7 5.9+ 2.4+ 2.4+

i00

100

75 3 3 6

12

17

60

5.28 0.24 0.96 2.40+ 2.40+ 0.72+

100

69 11.73 8 1.36 8 1.36 10 1.70 5+ 0.85+

52 7 8 18 7 8+

Total

100

i00

4.05 0.27 0.54 0.72

9

44 2 8 20+ 20+ 6+

16

51

45 3 6 S

16

1.08+

100

100

100

87 8 2 3

62

6

100

12.60 2.16 0.72 1.44

18

tr. 1

100

< 2p

100

10

Total in % of separate 100 Total in % of whole sample

B2g2 horizon: Quartz Feldspar Kaolinite M i c a (+ iltite) Sw. a n d e x p . (+ int) illite C h l o r i t e (+ s o i l c h l o r i t e ) Limonite Iron concretions

16-80p

17 28 2 10 30+ 20+ 6+ 2

2.80 0.20 0.10 3.00+ 2.00+ 0.80+ 0.20

99.9 69.6 5.9 4.2 10.3+ 3.4+ 4.7+ 0.2 1.6

100 11

10

99.9

TABLE III (continued) Separate and whole sample Cg horizon: Quartz Feldspar Kaolinite Mica (+ illite) Sw. and exp. (+ int) illite Chlorite (+ soil chlorite) Limonite Iron concretions

~ 80 ~

16-80 ~

77 3 3 6

6.17 0.63 0.63 1.26

79 7 3 7

45.82 4.06 1.74 4.06

3

0.63

4

2.32

8

1.68

Total in % of separate 100 Total in % of whole sample

100 21

2-16 p

45 7 8 18 14 8+

~ 2p

4.50 0.70 0.80 1.80 1.40 0.80+

100 58

27 2 10 27+ 24+ 8+ 2

Total

2.97 0.22 1.10 2.97+ 2.64÷ 0.88+ 0.22

69.5 5.6 4.3 10.1+ 4.0+ 4.6+ 0.2 1.7

100 10

11

100.0

1Swelling and/or expanded (+ intermediate) illite. 2tr. = trace cline) a r e s m a l l in all h o r i z o n s ; the A1 horizon has most, mainly K - f e l d s p a r which is m o r e r e s i s t a n t than N a - f e l d s p a r . Mica content is low in top l a y e r s , e s p e c i a l l y in the l e a c h e d A2g horizon. Small amounts of kaolinite p a r t i c l e s a r e m a i n l y found in the l o w e r h o r i z o n s . Kaolinite is not common in this s e p a r a t e , its usual p a r t i c l e s i z e being l e s s than 2 ~. In this c a s e , the m i n e r a l was c e m e n t e d to o t h e r p a r t i c l e s and did not b e c o m e wholly d i s p e r s e d when shaking the s a m p l e with 0.01 2v NaOH b e f o r e s e p a r a t i o n in the A t t e r b e r g c y l i n d e r s . The s a m e holds f o r expanded illite and swelling illite. The amounts of common chlorite and soil chlorite a r e a l s o s m a l l , e s p e c i a l l y in the top l a y e r s .

Separate 16-80 ~. The top h o r i z o n s , e s p e c i a l l y the A2g horizon, h a v e v e r y l a r g e amounts of quartz. Feldspar content (mainly K - f e l d s p a r ) is highest in the A1 h o r i z o n , although the amount is s t i l l r a t h e r s m a l l . Mica content is s m a l l , e s p e c i a l l y in the A2g horizon. Some fine kaolinite p a r t i c l e s a r e s t i l l c e m e n t e d to c o a r s e r m i n e r a l s of this s e p a r a t e in the s u b s o i l l a y e r s . C h l o r i t e content is s m a l l , e s p e c i a l l y in the top l a y e r . Separate > 80 p. The A1 and A2g h o r i z o n s c o n s i s t a l m o s t e n t i r e l y of quartz. The s e p a r a t e of the A2g horizon c o n s i s t s of pure quartz, which c l e a r l y d e m o n s t r a t e s the d i s a s t r o u s effect of w e a t h e r i n g and leaching, p a r t i c u l a r l y in this p a r t of the s o i l profile. The B2gl, B3g and Cg h o r i z o n s too, a r e v e r y r i c h in q u a r t z , viz., v a r y i n g f r o m 87 to 77%. However, the B2g2 horizon has only 45% quartz. Feldspar content, mainly K - f e l d s p a r , is low. This m i n e r a l is even a b s e n t in the A2g horizon. Mica content of the top l a y e r s is lower than in the subsoil l a y e r s . I n the A2g horizon this m i n e r a l too is absent. Minerals in ~ in the various profile horizons (Table Ill; Fig.10). T h e A1 and A2g h o r i z o n s c o n s i s t m a i n l y of q u a r t z , e s p e c i a l l y the A2g h o r i z o n . The o t h e r l a y e r s have somewhat s m a l l e r amounts, e s p e c i a l l y the B2g2 horizon. Geoderma, 2 (1968/1969)

143

l

Intensi__.ty_ Ceunts,'sec Crbltrory units

ChLorite

= ~07

A1

!

i

Intermediote Nw Zeatond

"~i ~

/

/

f / /

Koobnrte / i/t% ,.~ C~Lo,,t~ /' i '

Kool..... /

\d"

'

I '

:/

+ !

,i

q' "'W/OtyceroL

'

'

/ i

/

/

i I'

,,,,,W:tW~"

/ ~, ~ :i d~

A

j,

"~'

,' ft.," /

'~,,~ J i

It

Ii

I

I

/

:,:j "j '

I Chkomte / : , 13B #

71S

/t i

~o8 I i I It, • /

,A I; ,,:" /,U/k ,' ~/, /

;:,,o,.°l!

/\ l ~,71v

/I /,

,

i,, I!L\

~."',/,~ X~ / l i

J L/

oo:o°,

!

i/~,.<,:/,~o. :y/;,:,o_,o°m ~Y J

/,o,

/

'

i

~

II

Cg

~oo

1&O

350°

k50o

/

J,j >. ) kJ'

,id; .L zi, / i~,,:c,,, 1

~

'

/,,~ i)'t

1

erel '

V

h

Orl,inoL

t

Ka~ldnlte

,o!,

Glycerol

/

/

/

/

Vs / iI ~ /

i

//

110-120 cm

/~"

L/V

71

0 ~g no

/

SwI

iA

It i

!AJ

~Y"' ' ,i ,~oI I [~ ~ !1

'

ilv J'iX;J ~ ,i ]

/':~ /i

B,o

/,"~TXj/.oo Kaolinite Chtor rte

¢~ Olyce el

i'

> 50°

995

" It

/ SweU.ingittite Netherlands

1

t

,#

"~'rI",d'¢ ~o,i/V

I//

KooL,n,te

/ ,

,Uj

o.,,.,<

EI

Original i /

,k

,, K

/

'

i

/ 3500

G[..... [

,I W# / M

v' ~'

/.~v , I'k ~s~'s'.

/

~°°""""I~Ykl l

k /

,'

J

: :

m

/ 350c

' iii;)"t,/l :'i,, l// /

/ 'c,5, o

IF!*

I

f~ '

t

B 291

50-60cm

II

'

ill ^ ,

' 107

¢, 55C< F

//3 5O

I'

C~Lo,,~, /, ,]/

I

i 1[]!

A2g 25-35 cm

/

5-12 crn

2 8 DelltJl.el

depth (crn) OAI--

KaoLinite F~ntermediate • ~ ~Expohded itlite ~.. / \~wllting ittite /

'' 20

Mi©a

Fetdspar 7+

Ouartz

j/

~oit chlorite./",. [ChLor,t. j ~ / ' \

/

40-

S2gl- -

'\~I

~

"\, Concretions ~.,. ion

" '-..\ \

", ... ", -..

B292--

""--.p A": , Limo

B3g- -.

,

100

... .i

I,

1 Cg--. 12o-

100

60

percent ages

Fig.10. M i n e r a l o g i c a l composition (in %) of the p r o f i l e horizons. F e l d s p a r content is highest in the top soil l a y e r s , e s p e c i a l l y in the A1 horizon. The kind of f e l d s p a r in this c a s e is mainly K - f e l d s p a r and not N a - f e l d s p a r , which is l e s s r e s i s t a n t to weathering. The amount of f e l d s p a r is l o w e s t in the s u b s o i l horizons. K a o l i n i t e content is lowest in the top l a y e r s (A1 = 1.7%, A2g = 2.5%) and highest in the B2gl horizon (6.3%). M i c a and i l l i t e content is l e a s t in the topsoil l a y e r s , e s p e c i a l l y in t h e A2g horizon. The d e e p e r h o r i z o n s have l a r g e r amounts. W e a t h e r e d m i c a and i l l i t e m i n e r a l s ( i n t e r m e d i a t e , e x p a n d e d and s w e l l i n g i l l i t e ) show the s m a l l e s t q u a n t i t i e s in the A1 and A2g horizons and the highest in the illuviation h o r i z o n s . C h l o r i t e and s o i l c h l o r i t e a r e found l e a s t in the A1 and A2g h o r i z o n s . The amounts i n c r e a s e in the B2gl horizon and m a r k e d l y in the B2g2 horizon. The u n d e r l y i n g h o r i z o n s have somewhat s m a l l e r but s t i l l r a t h e r l a r g e amounts. C o n c r e t i o n s . Brown c o l o u r e d c o n c r e t i o n s of 0.5-1 cm o c c u r in the B2gl horizon and d e e p e r (Fig.10). The g r e a t e s t amount is found in the B2g2 horizon, viz., 3.0% of the total soil m a s s in this horizon ( T a b l e HI). Up to 45% of the t o t a l amount of the c o n c r e t i o n s of the p r o f i l e a r e c o n c e n t r a t e d in this h o r i z o n .

Fig.9. X - r a y d i f f r a c t i o n s p e c t r a of the s e p a r a t e s < 2 ~ f r o m the p r o f i l e h o r i z o n s and an i n t e r m e d i a t e and a swelling i l l i t e m i n e r a l . I = i l l i t e ; I t = i n t e r m e d i a t e i l l i t e ; S w . ] . = swelling illite; C h l . = c h l o r i t e ; S . C h . = s o i l c h l o r i t e ; M = mica. Geoderma, 2 (1968/1969)

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In the B2gl horizon, which has the highest amount of the f r a c t i o n < 2 p and of the Fe and A1 compounds, the amount of c o n c r e t i o n s is much lower than in the d e e p e r h o r i z o n s . By a n a l y s i s of the c o n c r e t i o n s t h e i r c o m p o s i t i o n was d e t e r m i n e d in % : K 2 0 = 1.65; Na20 = 0.70; CaO = 0.10; MgO = 0.66; Mn304 = 0.98; P205 = 0.21; TiO 2 = 1.71; F e 2 0 3 = 10.53; A1203 = 7.30; SiO2 = 69.85; ( H 2 0 ) - = 1.70; (H20) + = 4.30 (total = 99.69%). It follows that the c o n c r e t i o n s c o n s i s t m a i n l y of quartz. With some mica, f e l d s p a r and l i m o n i t e this is cemented with a m o r p h o u s s i l i c i c a c i d and sesquihydroxides. The s i z e of the c o n c r e t i o n s in this p r o f i l e is s m a l l as c o m p a r e d to that of the l a r g e r c o n c r e t i o n s (2-3 cm d i a m e t e r ) found in t r o p i c a l s e m i s u b h y d r i c s o i l s , in which s o m e t i m e s c o n c r e t i o n a r y h a r d p a n s of up to 1.5 m thick occur. C o n c r e t i o n s may be f o r m e d in s e v e r a l ways: by m i c r o b i o l o g i c a l activity; by p r e c i p i t a t i o n f r o m the p e r c o l a t i n g s o i l w a t e r ; f r o m ground w a t e r of different c o m p o s i t i o n in d e e p e r l a y e r s ; as a r e s u l t of p r e c i p i t a t i o n by e v a p o r a t i o n of ground w a t e r in dry s u m m e r p e r i o d s and by changes in the ground w a t e r c o m p o s i t i o n ( o x i d a t i o n - r e d u c t i o n potential). The p r e s e n c e of l i m o n i t e in the subsoil l a y e r s (Table III) w h e r e the c o n c r e t i o n s a r e m o s t abundant s u g g e s t s that the f o r m a t i o n of t h e s e two compounds is connected with the influence of the ground w a t e r , e s p e c i a l l y in the zone affected by s e a s o n a l fluctuations. In g e n e r a l , in c o a r s e t e x t u r e d gley p r o f i l e s an abundance of c o n c r e tions p r e s e n t s i t s e l f at the highest ground w a t e r level. In fine t e x t u r e d p r o f i l e s they even o c c u r at s o m e distance above this level. A p p a r e n t l y they a r e m o r e p r o f u s e at a g r e a t e r d i s t a n c e above the highest ground w a t e r level, where the s o i l is m o r e heavily textured. Both the h i g h e r r i s e of c a p i l l a r y w a t e r above the ground w a t e r level and the g r e a t e r w a t e r c a p a c i t y of the soil l a y e r s in the f i n e r t e x t u r e d s o i l s cause a g r e a t e r supply of soluble (iron) compounds which p a s s into a c c r e t i o n a r y or c o n c r e t i o n a r y f o r m s upon e v a p o r a t i o n or by m i c r o b i o l o g i c a l activity. This may explain the r e l a t i v e l y g r e a t c o n c e n t r a t i o n of conc r e t i o n s in t e x t u r a l B horizons. In the i n v e s t i g a t e d soil p r o f i l e , however, the l a r g e s t amount of conc r e t i o n s is not found in the horizon with the h e a v i e s t t e x t u r e (viz., B2gl). The abundance of c o n c r e t i o n s in d e e p e r h o r i z o n s m a y b e a r no r e l a t i o n to r e c e n t soil p r o c e s s e s , t h e i r o r i g i n being g o v e r n e d by totally d i f f e r e n t genetic f a c t o r s while in many c a s e s they may be f o s s i l f o r m a t i o n s . The m i c r o m o r p h o l o g i c a l i n v e s t i g a t i o n of the p r o f i l e a l r e a d y i n d i c a t e s this p o s s i b i l i t y . It is thus u n d e r s t a n d a b l e that the abundance of c o n c r e t i o n s may or may not coincide with c e r t a i n profile h o r i z o n s . DISCUSSION L e s s i v a g e (eluviation and illuviation of clay p a r t i c l e s ) , podzolization and g l e i z a t i o n a r e among the m o s t widely studied and d i s c u s s e d p r o c e s s e s in soil g e n e s i s . This p r o f i l e , studied in detail, shows evidence, that these t h r e e s o i l p r o c e s s e s o p e r a t e s i m u l t a n e o u s l y in it. The o p e r a t i n g p r o c e s s e s in s o i l s , however, a r e not a l w a y s e x p r e s s e d 146

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in the morphology of the soil profile to the extent that they are effective within the soil. In the nomenclature of soils the soil profiles a r e given names a c c o r d i n g to the dominating and actual p r o c e s s or to the morphological c h a r a c t e r i s t i c s of the profile, which often are thought to reflect the important active p r o c e s s or p r o c e s s e s . In our hydromorphic soil profile the gley phenomena are m o r p h o l o g ically obvious c h a r a c t e r i s t i c s of wetness, indicating the gleization p r o c e s s . The same holds true for the clay movement, which is m o r p h o l o g i c a l l y well expressed by the development of the textural B-horizon. This s e c t i o n shows~in the illuvial horizon, the o c c u r r e n c e of oriented clay skins, of which fossil and recent ones can be observed. The breakdown ("dissolution") of the preciously f o r m e d cutan-like formations under influence of r e d u c i n g c i r c u m s t a n c e s , and the formation of speckled argillans is a clear indication that gley formation and part of the displacement of clay minerals have t a k e n place simultaneously. Evidences of podzolization are morphologically mainly visible in t h e upper l a y e r s of the profile, viz., limited mineralization of the organic matter and the concentration of some displaced humus in a completely bleached layer just below the Al-horizon. In arable land these features may disappear completely. C h e m i c a l l y the podzolization p r o c e s s is clearly revealed by a break-up of the clay minerals and the predominance of kaolinite in the clay fraction. Data obtained from chemical analyses confirms the podzolization p r o c e s s by the low values of the exchangeable cations and the F e - and A1 contents in t h e top layers. The decomposition and the vertical displacement of both weathered and unweathered components, together with the difference in the SiO2/R2 O 3 ratios in A and B horizons, indicate that the podzolization p r o c e s s e s are outstanding. This is the most striking point of difference of the hydromorphic loess f r o m the well drained loess soils of this region, in which only clay eluviation occurs. In this respect there is an urgent n e e d for investigations on the composition of the organic m a t t e r in the top l a y e r s and the role it plays in the eluviation of metal cations. A knowledge of the different active organic compounds which vary with the c o m p o s i t i o n of the soil solution, is of the greatest importanc~ in understanding the genesis of podzols, podzolic gley soils, gley soils and related soil t y p e s . Van Schuylenborgh (1962) considers that "the soil formation p r o c e s s , responsible for the formation of podzols, grey brown podzolic soils and g l e y - s o i l s , is essentially the same". This statement can easily be m i s understood. As is shown by the analyses, evidences a r e present of at l e a s t three p r o c e s s e s acting concurrently in this hydromorphic loess soil. In classifying this soil to soil forming p r o c e s s e s each of the three p r o c e s s e s can be distinguished and defined separately. There is extensive literature (Van der Marel and Van den Broek, 1968) dealing with these soil p r o c e s s e s in a comprehensive and very detailed manner, although it is often very confusing. genesis seem to a t t r a c t f r e s h attention periodically, e.g., action of c h e l a t e s , humic acids, b a c t e r i o l o g i c a l activity, etc. Several p r o c e s s e s , indicated by a certain t e r m , still a r e complex p r o c e s s e s . The most important ones, which play a role in the hydromorphic soil can be s u m m a r i z e d as f o l l o w s : Gleization: the p r o c e s s of reduction of soil compounds, induced by Geoderma, 2 (1968/1969)

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p e r m a n e n t o r s e a s o n a l w a t e r logging o r e x c e s s of w a t e r in t h e p r o f i l e , by w h i c h g r e y o r blue c o l o u r e d h o r i z o n s a r e p r o d u c e d . R e d u c t i o n of the i r o n c o m p o u n d s in this p r o c e s s p r e d o m i n a t e s the i n f l u e n c e of b a c t e r i a l a c t i v i t y . The t e r m s e l u v i a t i o n and i l l u v i a t i o n a r e u s e d f o r m o v e m e n t a n d d e p o s i t i o n of s o i l p a r t i c l e s in the s o i l p r o f i l e . S e v e r a l t e r m s a r e i n d i c a t i v e of the s t a t e of the m o v i n g p a r t i c l e s and the k i n d of d i s p l a c e m e n t : Lessivage: a F r e n c h t e r m o r i g i n a l l y , u s e d f o r the p r o c e s s of m i g r a t i o n and d e p o s i t i o n of u n a l t e r e d c l a y s i z e d p a r t i c l e s in the s o i l p r o f i l e . Illimerization: b e c a u s e the t e r m l e s s i v a g e l i t e r a l l y h a s a w i d e r m e a n i n g than m o v e m e n t of c l a y p a r t i c l e s only, F r i d l a n d (1958) i n t r o d u c e d the t e r m i l l i m e r i z a t i o n f o r the p r o c e s s of d o w n w a r d m o v e m e n t ( m i g r a t i o n ) of u n a l t e r e d c l a y p a r t i c l e s and r e d e p o s i t i o n of t h e m in an i l l u v i a l l a y e r . Soluviatio~z: e l u v i a t i o n a f t e r s o l u t i o n of m i n e r a l c o m p o n e n t s , which a r e l e a c h e d and r e m o v e d f r o m the s u r f a c e l a y e r s . Cheluuiatio~l: e l u v i a t i o n t o g e t h e r with c h e l a t i o n ( " c o m p l e x i n g " by r i n g s t r u c t u r e d o r g a n i c c o m p o u n d s ) of s o i l p a r t i c l e s , e s p e c i a l l y F e and A1 o x i d e s . I l l i m e r i z a t i o n and c h e l u v i a t i o n f o r m the two ends of a s e q u e n c e of eluviation processes. In the one end of the s e q u e n c e the p r o c e s s e s a r e r e s t r i c t e d to i l l i m e r i z a t i o n and s o m e s o l u v i a t i o n ( r e m o v a l of c a t i o n s f r o m s u r f a c e l a y e r s and r e d e p o s i t i o n at depth). The o t h e r end i s i n d i c a t e d a s p o d z o l i z a t i o n , which r e f e r s to c h e l u v i a t i o n and s u b s e q u e n t s t r o n g d e c o m p o s i t i o n of the m i n e r a l s o i l p a r t i c l e s a s d e f i n e d by the d e c r e a s e of the S I O 2 / R 2 0 3 r a t i o s f r o m A to B h o r i z o n . T h i s m i n e r a l d e c o m p o s i t i o n m a y be i n t e n s i f i e d in s o i l s , w h e r e the g l e i z a t i o n p r o c e s s is a c t i v e and can then h a r d l y be d i s t i n g u i s h e d f r o m it, a s in the p r o f i l e of t h i s study. D u r i n g the 1966 c o n f e r e n c e of the I n t e r n a t i o n a l S o c i e t y of Soil S c i e n c e in Spain, a new t e r m , argilluviation, s e e m s to have b e e n c o i n e d f o r the c l a y m i g r a t i o n ( e l u v i a t i o n ) u n a e r m e d i t e r r a n e a n c l i m a t i c c o n d i t i o n s . Not e a s i l y d e f i n a b l e s o i l p r o c e s s e s thus a p p e a r to d e m a n d a s o m e t i m e s r a t h e r vague i n d i c a t i o n of the e x t e r n a l e n v i r o n m e n t a l f a c t o r s . The d i f f i c u l t i e s in e x a c t l y d e t e r m i n i n g the o p e r a t i n g s o i l p r o c e s s e s , e s p e c i a l l y when they i n t e r a c t , a l s o a f f e c t the c l a s s i f i c a t i o n of the p r o f i l e s . None of the p r o c e s s e s d e s c r i b e d in t h i s p r o f i l e i s c l e a r l y p r e d o m i n a n t o v e r the o t h e r s . T h e r e l o r e , the p r o f i l e can b e c l a s s i f i e d in d i f f e r e n t w a y s , d e p e n d i n g on the c l a s s i f i c a t i o n c r i t e r i a s e l e c t e d and the i n t e r p r e t a t i o n of m o s t of the i n d i v i d u a l s o i l c h a r a c t e r i s t i c s . The n o m e n c l a t u r e f o r the s o i l p r o f i l e s r e f e r s e i t h e r to the d o m i n a n t p r o c e s s o r to the p r o f i l e c h a r a c t e r i s t i c s , d e p e n d i n g on t h e c l a s s i f i c a t i o n s y s t e m u s e d . The n a m e s g l e y and p o d z o l " h o w e v e r " a r e u s e d both a s m o r p h o l o g i c a l t e r m s a n d to i n d i c a t e a p r o c e s s . In t h e c l a s s i c c o n c e p t of p o d z o l s t h e p o d z o l i z a t i o n p r o c e s s is d e f i n e d on c h e m i c a l c o m p o s i t i o n : low pH, low b a s e s t a t u s and a c c u m u l a t i o n of s e s q u i o x i d e s . T h e i n v e s t i g a t e d h y d r o m o r p h i c loess profile has these characteristics. In the y o u n g e s t m o r p h o m e t r i c c l a s s i f i c a t i o n s y s t e m s t h e s o i l s a r e c l a s s i f i e d on t h e i r v i s i b l e and i n t e r n a l p r o p e r t i e s t h a t r e f l e c t s o i l g e n e s i s . F o r p o d z o l s the p r e s e n c e of an a c c u m u l a t i o n h o r i z o n of c o l l o i d a l h u m u s i s d e c i s i v e . In the s o i l p r o f i l e of this s t u d y t h i s c r i t e r i u m is l a c k i n g . A c c o r d i n g to the 7th A p p r o x i m a t i o n of t h e U.S. Soil S u r v e y (1960) it b e l o n g s to the s o i l s with an a r g i l l i c h o r i z o n a n d e v i d e n c e of w e t n e s s . A s a

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consequence of the low b a s e s a t u r a t i o n , which is l e s s than 35% t h r o u g h o u t the p r o f i l e , this profile m u s t be c o n s i d e r e d as aquult and b e c a u s e of t h e u r a b r i c s u r f a c e horizon as umbraquult. When r e g a r d i n g the white p a t c h e s in the B horizon as an albic horizon that tongues into the B horizon, t h e s o i l can be reckoned among the a l f i s o l s , in which c a s e it will be a g l o s s a q u a l f . These soil n a m e s c h a r a c t e r i z e the morphology of the p r o f i l e exactly a n d connote the qualitative dominance of the c h a r a c t e r i s t i c s . However, p o d z o l ization c h a r a c t e r i s t i c s a r e not taken into c o n s i d e r a t i o n b e c a u s e the r e q u i r e d m o r p h o l o g i c a l e x p r e s s i o n is lacking. The Dutch c l a s s i f i c a t i o n s y s t e m t r e a t s the p r o f i l e a l m o s t in the s a m e way, putting it into the o r d e r of s o i l s with a t e x t u r a l B horizon. On a l o w e r l e v e l the c h a r a c t e r i s t i c s of wetness a r e u s e d as a d i f f e r e n t i a t i n g c r i t e r i o n . In Dutch the soil has been named " k u i l b r i k g r o n d " (De B a k k e r and S c h e l l i n g , 1966). In other c l a s s i f i c a t i o n s y s t e m s b a s e d on the concept of t e r r e s t r i a l and s e m i - t e r r e s t r i a l p r o f i l e development, the gley c h a r a c t e r i s t i c s a r e the dominant c r i t e r i a f o r c l a s s i f i c a t i o n , allowing this p r o f i l e to be r e c k o n e d among the gley s o i l s . The c h e m i c a l and m i n e r a l o g i c a l i n v e s t i g a t i o n s (Fig.6,9,10) of the i n v e s t i g a t e d p r o f i l e c l e a r l y show e v i d e n c e s of podzolization. The d e s i g n a t i o n of the p r o f i l e as a podzol is j u s t i f i e d when these a n a l y t i c a l data a r e u s e d a s c r i t e r i a for c l a s s i f i c a t i o n . Podzolization in this l o e s s i a l p a r e n t m a t e r i a l m a y be linked with the gleization. As a m a t t e r of fact the t e x t u r a l B horizon is at the s a m e t i m e t h e podzol B horizon. M o r p h o l o g i c a l l y this f e a t u r e is h a r d l y d i s c e r n a b l e n o r evident f r o m the m i c r o m o r p h o l o g i c a l investigation. M o r p h o l o g i c a l l y it i s m a i n l y the top soil l a y e r that s u p p l i e s i n f o r m a t i o n about the p o d z o l i z a t i o n . Evidence is found h e r e in the slow d e c o m p o s i t i o n of o r g a n i c m a t e r i a l a n d d i s p l a c e m e n t of d i s p e r s e d humic m a t e r i a l to a depth of about 20 cm in the m i n e r a l soil. However, these phenomena d i s a p p e a r c o m p l e t e l y when t h e s e s o i l s a r e c o n v e r t e d into a r a b l e land. Tillage, f e r t i l i z i n g and other t r e a t m e n t s change the c h a r a c t e r of the topsoil and e l i m i n a t e the m o s t i m p o r t a n t m o r p h o l o g i c a l c h a r a c t e r i s t i c s of podzolization. In c l a s s i f y i n g these c u l t i vated s o i l s , g r e a t e m p h a s i s is t h e r e f o r e given to the B horizon of w h i c h the clay illuviation p r e d o m i n a t e s . The Dutch and A m e r i c a n c l a s s i f i c a t i o n s y s t e m s a g r e e in this r e s p e c t . Whether clay m i g r a t i o n is to be c o n s i d e r e d m o r e i m p o r t a n t than the g l e y - c h a r a c t e r i s t i c s , m a y be a m a t t e r of o p i n i o n . It is, however, i m p o r t a n t to note that full u n d e r s t a n d i n g of soil g e n e s i s and n e c e s s a r y i n f o r m a t i o n on soil p r o c e s s e s can be d e r i v e d by c o m b i n i n g c h e m i c a l , m i n e r a l o g i c a l and m i c r o m o r p h o l o g i c a l a n a l y s e s . This holds t r u e e s p e c i a l l y f o r the p r o c e s s e s of podzolization, the d e v e l o p m e n t s of w h i c h in our p r o f i l e a r e not sufficient f o r i m m e d i a t e m o r p h o l o g i c c l a s s i f i c a t i o n , but which a r e c l e a r l y d e t e c t a b l e in c h e m i c a l s o i l a n a l y s e s . N o t w i t h s t a n d i n g the n u m e r o u s i n v e s t i g a t i o n s , the c l a s s i f i c a t i o n of gley s o i l s , podzols, p o d z o l i c gley s o i l s and p r o f i l e s with r e l a t e d genetic p r o c e s s e s is f a r f r o m being p r e c i s e and c l e a r . This p r o f i l e t h e r e f o r e is a v e r y good e x a m p l e of a soil at the p e d o l o g i c a l i n t e r s e c t i o n of d i f f e r e n t genetic and c l a s s i f i c a t o r y i n t e r p r e t a t i o n s .

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