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Red Mediterranean Soils: Nature, Properties, and Management of Rhodoxeralfsin Northern GreeceChristos Noulas a; Theodore Karyotis a; Athanasios Charoulis a; Ioannis Massas b

a National Agricultural Research Foundation, Institute for Soil Mapping and Classification, Larissa, Greece b

Agricultural University of Athens, Laboratory of Soil Science and Agricultural Chemistry, Athens, Greece

Online Publication Date: 01 January 2009

To cite this Article Noulas, Christos, Karyotis, Theodore, Charoulis, Athanasios and Massas, Ioannis(2009)'Red Mediterranean Soils:Nature, Properties, and Management of Rhodoxeralfs in Northern Greece',Communications in Soil Science and PlantAnalysis,40:1,633 — 648

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Red Mediterranean Soils: Nature, Properties, andManagement of Rhodoxeralfs in Northern Greece

Christos Noulas,1 Theodore Karyotis,1 Athanasios Charoulis,1 and Ioannis

Massas2

1National Agricultural Research Foundation, Institute for Soil Mapping and

Classification, Larissa, Greece2Agricultural University of Athens, Laboratory of Soil Science and Agricultural

Chemistry, Athens, Greece

Abstract: The studied Alfisols were developed on Quaternary calcareous deposits

and belong to the great group of Rhodoxeralfs. They occur usually in the meso-

Mediterranean bioclimatic zone and are affected by water deficit during the

summer period. They are located mainly on backslope geomorphic surfaces, old

terraces, and alluvial fans, and their erodibility is medium to low. Trends of

decreased iron content in the deeper soil layers due to severe drainage conditions

may be responsible for relatively low values of free iron oxides (Fed). The rather

limited variation of Fed may reflect the specific pedogenetic conditions in which

red soils were formed. Indices of pedogenesis [Feo/Fed (Feo: amorphous Fe), Fed–

Feo, and iron illuviation index of Fed] indicated that the studied pedons are at

different stages of development. Redness indices (RI) of Bt horizons in pedons

were found in the following decreasing order: P1 5 P5 . P4 5 P6 . P2 . P3.

There were no clear trends of free manganese oxide (Mnd) distribution with

depth. The lack of correlation between Mnd and clay or Fed suggested that Mnd

oxides do not take part in the co-illuviation of clay and Fed oxides. Acidity, low

content of organic carbon, exchangeable potassium (K+), available phosphorus

(P), and water deficit are the main impediments to crop production on these soils.

Geomorphological and physicochemical properties suggest that rotation schemes,

minimum tillage, liming practices, soil leveling, use of proper irrigation systems,

and micronutrient application are among the suggested practices to sustain crop

production and mitigate erosion risk.

Address correspondence to Dr. Theodore Karyotis, 1 Theophrastou Str.,

41335, Larissa, Greece. E-mail: karyotis@hellasnet.gr

Communications in Soil Science and Plant Analysis, 40: 633–648, 2009

Copyright # Taylor & Francis Group, LLC

ISSN 0010-3624 print/1532-2416 online

DOI: 10.1080/00103620802694381

633

Keywords: Iron oxides, manganese oxides, pedogenesis, soil management

INTRODUCTION

Red soils in Greece are grouped into two categories: 1) autochthonous,

located on hard limestone or marble in mountainous or hilly and sloping

landscapes and 2) allochthonous, distributed on the Tertiary and

Pleistocene surfaces of the lowlands (Yassoglou et al., 1997). They are

distributed in the thermo and meso–Mediterranean bioclimatic zone

(UNESCO/FAO, 1963). These soils belong to the great groups of

Rhodoxeralfs, Xerochrepts, or Xerorthents (Yassoglou, Kosmas, and

Moustakas 1997). Their red color is mainly attributed to hematite formed

during rubification in the long dry summer period, which is the dominant

diagnostic characteristic of terra rossa (Schwertmann and Taylor 1989;

Boero and Schwertmann 1989). Differences in geology, lithology, and

geo-ecosystems of different areas of the Mediterranean basin (Yaalon

1997) make the classification of terra rossa controversial. Some decades

ago, Kubiena (1953) reported characteristic red or brown-red soils (terra

rossa) in southern Europe, which now are rare. Cardoso (1965) stressed

that soils in the Mediterranean region were formed on limestone and that

argillic (Bt) horizons were developed in situ, but the climatic conditions

were different from present ones. As pointed out by Fedoroff (1997),

early research on the genesis of red Mediterranean soils ignored clay

illuviation, and several concepts were proposed to explain the genesis of

these soils (Durand 1959). As far as the age of soils is concerned, it is

generally recognized that their formation begun preholocenic, so these

soils have been exposed to different climatic conditions (Fedoroff 1997)

and to long-term anthropogenic factors (Yaalon 1997).

Red (allochthonous) soils of Thrace, Greece, were developed on

Quaternary calcareous deposits, belong to the great group of

Rhodoxeralfs, and are located on several geomorphic surfaces on

moderately to gently sloping landscapes (Yassoglou, Kosmas, and

Moustakas 1997; Haidouti et al. 2001). However, the pedogenetic

environment, classification, and red pigmentation of red soils in the

Mediterranean basin are still a matter of controversy because of the high

soil diversity. Additionally, the Mediterranean climate is characterized by

several dry months, and the length of summer drought defines the xeric

soil moisture regime. It is characterized by winter rainfall in excess of

evapotranspiration, and it is not restricted to the Mediterranean region

but is present also in Africa, Americas, Asia, and Australia (Engel, Witty,

and Eswaran 1997). Therefore, obtaining accurate data on the nature and

properties of the soils at different landscapes assists in sustainable land

634 C. Noulas et al.

management, to prevent and mitigate soil degradation. In this study, we

described selected morphological, physical, and chemical properties of

certain Rhodoxeralfs of northern Greece with special attention to their

iron (Fe) and manganese (Mn) oxides. Moreover, appropriate interven-

tions and practices for sustained land and crop management are suggested.

Study Area

A detailed soil survey (scale 1:10,000) was carried out in a part of Rodopi

Prefecture (Thrace) located in northern Greece, and a soil map in the

region (latitude: 22 W, 24 E, 42 N, 40 S) was compiled (Haidouti et al.

1994). The studied soils (Figure 1) have been classified as Alfisols and

belong to the great group of Rhodoxeralfs (Soil Survey Staff 1998).

According to Munsell Soil Color Charts (1994), the examined soilsexhibit hue 2.5YR or 5YR. Description and morphological properties are

presented in Table 1. Observations during the field survey indicated

Figure 1. Simplified map of the sampling positions in the Prefecture of Rodopi

(Thrace, northern Greece).

Nature and Management of Mediterranean Rhodoxeralfs 635

Table 1. Morphological and physical properties of the studied Rhodoxeralfs

Profilea Land

use

Landscape

position

Slope

(%)

Horizons Depth

(cm)

Textureb Clay

(%)

Clay

B/C

Structurec Moist color

(Munsell)

Horizon

boundaryd

P1 Wheat Backslope 2–6 Bt1 0–25 C 44.4 2.25 3mabk 2.5YR 3/6 C

Bt2 25–48 C 40.4 2.05 3mabk 2.5YR 3/6 C

C 48–90 SL–SCL 19.7 struct. less 5YR 4/6

P2 Cotton

Wheat

Backslope 6–12 AE 0–18 SCL–SL 19.8 1msbk 7.5YR 4/4 C

Bt1 18–33 SC 38.7 1.35 3msbk 2.5YR 4/6 G

Bt2 33–47 SCL–SC 34.7 1.21 3msbk 5YR 4/6 G

C 47–80+ SCL 28.7 struct. less 7.5YR 5/6

P3 Wheat

Cotton

Backslope 6–12 AE 0–22 SCL 27.8 massive 5YR 4/6 C

Bt1 22–38 SC 37.5 1.27 2msbk 5YR 4/6 C

Bt2 38–75 C 64.5 2.19 3mabk 5YR 4/6 G

Ck1 75–103 CL–SCL 29.5 msbk 7.5YR 4/4

P4 Cotton Terrace 2–6 EB 0–20 L–SCL 21.8 massive 5YR 4/6 A

Bt1 20–39 SCL 25.2 1.08 2msbk 2.5YR 4/6 C

Bt2 39–61 SCL–CL 27.3 1.17 2msbk 2.5YR 4/6 C

BC 61–82 L–SCL 23.4 1msbk 2.5YR 4/6

P5 Cotton Terrace 0–2 E 0–22 SL 10.4 1msbk 7.5YR 4/4 C

EB 22–41 SCL 21.0 1msbk 7.5YR 4/4 G

Bt1 41–72 SCL 32.0 1.10 3msbk 2.5YR 3/6 G

Bt2 72–108 SC–SCL 35.1 1.21 3msbk 2.5YR 3/6 D

BC 108–137 SCL 29.1 2msbk 2.5YR 3/6

63

6C

.N

ou

las

eta

l.

Profilea Land

use

Landscape

position

Slope

(%)

Horizons Depth

(cm)

Textureb Clay

(%)

Clay

B/C

Structurec Moist color

(Munsell)

Horizon

boundaryd

P6 Wheat Shoulder 2–6 BE 0–22 SCL–SC 35.0 massive 5YR 4/4 A

Bt1 22–51 SC–C 44.7 1.02 3mabk 2.5YR 4/6 C

BC 51–75 SC 36.7 3mabk 2.5YR 4/6 C

C 75–97 C 43.7 2msbk 2.5YR 4/4

aOrder 5 Alfisol, suborder 5 Xeralf, great group 5 Rhodoxeralfs, subgroup 5 typic (P3 5 calcic).bC 5 clay (,2 mm), S 5 sand (.50 mm), L 5 silt (2–50 mm).c1 5 weak, 2 5 moderate, 3 5 strong, m 5 medium, abk 5 angular blocky, sbk 5 subangular blocky.dA 5 abrupt, C 5 clear, G 5 gradual.

Table 1. Continued

Na

ture

an

dM

an

ag

emen

to

fM

editerra

nea

nR

ho

do

xera

lfs6

37

well-drained conditions (absence of water table within the soil profile

depth, limited mottling). The studied soils exhibit criteria of the

allochthonous red soils, namely, they are located on moderately to gently

sloping landscapes, erodibility is low to medium, and the erosion risk is

medium to high. The landscape position is compiled in Table 1, and soils

are located mainly on alluvial deposits and/or Pleistocene formations.

Slope phases of pedons ranged from flat (0–2%) in P5 to slight (2–

6%) in P1, P4, and P6 and moderate (6–12%) in P2 and P3 (Table 1).

Cotton is preferably grown on flat or various slopes (Table 1) and wheat

on the slightly or moderately sloping areas. Moderate erosion has

occurred on pedons P2, P3, P4, and P6, moderate to strong erosion on

P1, and slight or none on P5.

The studied soils occur in the meso-Mediterranean bioclimatic zone

(UNESCO/FAO 1963) of northern Greece. According to meteorological

data provided by the National Meteorogical Service in Komotini (31 m

a.s.l.), mean air temperature for the period 1955 to 1993 was 14.8 uC(maximum 30.4 uC in August and minimum 1.4 uC in January). For the

same period, mean annual precipitation was 665 mm, and mean relative

humidity was 66%. There is a fluctuation in the mean seasonal

precipitation, and moisture deficit occurs from mid-June to mid-

September. The root zone during summer remains dry for more than

45 days after summery equinox, defining the soil moisture regime as xeric

(Soil Survey Staff 1998).

MATERIALS AND METHODS

Soil samples were collected from each soil horizon, air dried, and sieved

(,2 mm) for laboratory analyses. Particle-size distribution was deter-

mined by the Bouyoucos hydrometer method (Gee and Bauder 1986).

The pH was measured in a 1:1 soil–H2O suspension (McLean 1982).

Ammonium acetate (1M at pH 7) was used for exchangeable cations

(Thomas 1982). The exchangeable K+ and sodium (Na+) were determined

with a flame photometer, and calcium (Ca2+) and magnesium (Mg2+)

were determined with an atomic absorption spectrophotometer. Cation

exchange capacity (CEC) was determined by the ammonium acetate

method (Rhoades 1982). A modified wet-digestion Walkley and Black

method (Nelson and Sommers 1982) was used for the organic carbon

determination. Free iron (Fed) and manganese (Mnd) oxides were

extracted by the Na citrate–bicarbonate–dithionite method (CBD)

(Mehra and Jackson 1960), whereas amorphous Fe (Feo) was extracted

by the ammonium oxalate method (Blume and Schwertmann, 1969;

Alexander, 1974). Plant-available Fe, Mn, zinc (Zn), and copper (Cu)

were extracted with diethylenetriaminepentaacetic acid (DTPA) and

638 C. Noulas et al.

determined by atomic absorption spectroscopy (AAS) (Page 1982). Olsen

or Bray I method was used for measuring plant-available phosphorus (P)

(Page 1982), and the azomethine–hydrogen method (Keren 1996) was

used for the soil-available boron (B).

The formula of Torrent, Schwertmann, and Schulze (1980) was used

for the calculation of redness index: RI 5 (hue 6 chroma) / value.

Chroma and value are the numerical values from the Munsell Soil Color

Charts (1994), and hues are 7.5 for 2.5YR, 5 for 5YR, and 2.5 for 7.5YR.

Illuviation index of Fed was II Fed: 5 Fed eluvial horizon / Fed Bt

horizon (Bech et al. 1997). All correlations between various parameters

and summary statistics were performed in SPSS (SPSS Inc. 2001).

RESULTS AND DISCUSSION

Morphological and Physicochemical Properties

The landscape position and the slope phases of each soil profile are

presented in Table 1 and have been described in a previous section of this

study. All pedons exhibit well-developed argillic (Bt) horizons overlying

on a C or BC horizon (Table 1). In P1, the argillic horizon is at the

surface as a consequence of erosion. The clay content in the surface

horizons ranged between 10 and 35% and in the argillic horizons was

between 25 and 65%. Mean values of sand, silt, and clay were 50, 18, and

32%, respectively.

The structure in the Bt horizons is moderate to strong angular or

subangular blocky, and the horizon boundaries are mostly clear or

gradual. A calcic horizon was formed in P3, indicating that dissolved

carbonates leached out and re-precipitated within a depth between 75 and

103 cm from the soil surface (Table 1), as a consequence of induced

climatic processes (Yaalon 1982).

Soil pH is acidic in eluvial and Bt horizons, and the lowest values

were observed in the upper soil layers, reflecting the removal of

exchangeable bases to the deeper horizons. In P2 and P4, recent and

extensive use of acidifying fertilizers further reduced the pH values.

Organic carbon (C) content ranged between 0.7 and 16.9 g kg21 as it is

common for the most Greek arable soils (Yassoglou 1995) and decreased

with depth in all profiles (Table 2) as a process of soil development.

Fertilization and/or secondary enrichment after weathering and

transportation of the adjacent alluvial lime material have increased base

saturation in the topsoil (51–98%; Table 2). Among exchangeable

cations, Ca2+ and Mg2+ were the dominant ones with an average content

of 8.7 and 8.3 cmol(+)kg21, respectively. Contents of exchangeable K+ and

Na+ were rather low in all soil profiles representing a small part of CEC.

Nature and Management of Mediterranean Rhodoxeralfs 639

Table 2. Chemical properties of the studied soils

Profile Horizon Exchangeable (cmol(+)kg21) CECa

(cmol(+)kg21)

BSb

(%)

DTPA trace elements (mgkg21) Pavailable

(mgkg21)

SOCc

(gkg21)

pH

(1:1)K+ Na+ Ca2+ Mg2+ Fe Cu Zn Mn B

P1 Bt1 2.41 0.28 6.59 8.63 23.9 74.9 4.35 3.16 0.32 25.50 1.58 3.73 7.9 5.9

Bt2 2.00 0.32 8.26 12.67 29.8 78.0 2.50 1.29 0.17 11.52 0.78 2.36 2.6 6.6

C 1.41 0.32 8.44 8.14 18.7 97.9 2.44 0.49 0.14 5.17 0.34 3.85 0.8 6.9

P2 AE 0.92 0.19 5.99 6.72 17.2 80.3 21.40 0.60 0.91 45.40 0.78 9.63 16.9 4.9

Bt1 0.28 0.28 7.39 13.22 32.6 64.9 6.39 0.50 0.30 1.71 0.34 3.35 4.9 5.1

Bt2 0.41 0.41 6.56 12.37 32.4 61.0 4.87 0.40 0.26 1.00 0.23 2.48 2.6 5.4

C 0.65 0.65 6.82 12.62 30.1 68.9 4.11 0.30 0.25 1.32 0.23 3.10 0.8 5.9

P3 AE 0.59 0.24 10.51 2.67 17.4 80.5 2.60 0.53 0.35 3.09 0.68 7.76 7.6 6.0

Bt1 0.46 1.17 8.47 7.44 30.7 57.1 7.10 0.88 0.12 2.94 0.78 1.99 7.6 6.6

Bt2 0.36 1.52 10.61 13.18 35.2 72.9 3.37 0.22 0.07 2.19 1.91 1.24 5.0 6.8

Ck1 0.23 1.09 12.86 7.99 20.3 100.0 3.34 0.25 0.21 2.14 1.11 1.24 2.9 7.8

P4 EB 0.69 0.39 4.62 3.83 18.8 50.7 16.40 1.10 0.60 52.50 0.68 3.60 6.0 5.3

Bt1 0.72 0.37 5.82 7.61 20.7 70.1 10.08 0.90 0.31 17.69 0.78 5.09 2.3 5.8

Bt2 0.64 0.41 6.25 8.25 26.8 58.0 6.11 0.80 0.25 17.83 1.24 1.49 1.7 5.8

BC 0.59 0.44 6.12 7.78 20.9 71.4 8.16 0.80 0.23 16.28 0.68 0.87 1.2 6.0

P5 E 0.64 0.19 5.94 2.36 9.3 98.2 18.20 2.50 1.36 26.58 0.34 65.30 10.5 5.5

EB 0.46 0.17 6.09 2.05 17.2 51.0 2.84 1.14 0.37 6.98 0.45 74.61 5.0 6.2

Bt1 0.64 0.19 8.67 3.23 13.7 92.9 3.10 0.88 0.15 7.79 0.23 5.34 4.6 6.7

Bt2 0.77 0.41 9.29 6.46 17.8 95.1 3.69 0.57 0.19 4.42 0.23 2.23 2.1 6.7

BC 0.59 0.32 7.82 7.14 17.8 89.2 3.49 0.69 0.20 4.14 0.34 7.32 1.7 7.5

64

0C

.N

ou

las

eta

l.

Profile Horizon Exchangeable (cmol(+)kg21) CECa

(cmol(+)kg21)

BSb

(%)

DTPA trace elements (mgkg21) Pavailable

(mgkg21)

SOCc

(gkg21)

pH

(1:1)K+ Na+ Ca2+ Mg2+ Fe Cu Zn Mn B

P6 BE 0.82 0.39 11.20 9.10 33.2 64.8 14.25 1.50 0.48 50.00 0.90 10.24 11.1 4.5

Bt2 0.46 0.44 15.43 12.07 36.2 78.5 3.51 1.00 0.29 2.84 0.90 3.60 3.9 6.4

BC 0.36 0.64 14.78 11.14 27.6 97.5 2.39 0.60 0.20 2.48 0.68 2.36 1.3 7.4

C 0.41 1.31 14.80 12.50 29.6 98.0 1.50 0.60 0.13 1.40 0.45 2.86 0.7 7.6

aCEC 5 cation exchange capacity.bBS 5 base saturation.cSOC 5 soil organic carbon.

Table 2. Continued

Na

ture

an

dM

an

ag

emen

to

fM

editerra

nea

nR

ho

do

xera

lfs6

41

Although Greek soils contain sufficient amounts of exchangeable

potassium, it seems that the studied red soils constitute an exception

(Haidouti et al. 2001). No clear trends with depth were observed for

exchangeable K+, whereas Na+, a more mobile element, was generally

increased. Cation exchange capacity ranged from 9.3 to 36.2 cmol(+)kg21;

mean value was 24.1 cmol(+)kg21 and was correlated (r 5 0.74, P , 0.001,

n 5 24) to the clay content. Drainage conditions have promoted

decalcification, illuviation, and differentiation of the soil layers (Darwish

and Zurayk 1997).

Available micronutrients Fe, Cu, Zn, and B were generally less than

the sufficiency levels to sustain crop production in all pedons (Mengel

and Kirkby 1979; Martens and Lindsay 1990), confirming previous

studies in Greek soils (Haidouti et al. 2001). Surface horizons were rich in

Mn and Cu, and certain horizons of P1, P5, and P6 contained sufficient

amounts. Contents of Fe and Mn decreased with depth, and this may

reflect the degree of weathering of Fe–Mn minerals. The level of B ranged

between 0.23 and 1.91 mg kg21 (mean 0.69 mg kg21), and was related to

clay content (r 5 0.53, P 5 0.007, n 5 24). Available P within the E and

EB horizons of P5 (Table 2) was sufficient (Olsen and Sommers 1982) due

to P overfertilization.

Iron and Manganese Oxides

The total amount of Fed observed considerably higher than Feo,

indicating the low content of poorly crystalline Fe oxides (Table 3).

These trends confirm results of previous studies in central or northern

Greece (Karyotis, Kosmas, and Yassoglou 1996; Haidouti et al. 2001).

Fed oxides show maxima in the Bt of all soils. The similar pattern of

depth distribution of Fed oxides and clay is an indication of their co-

emigration to the Bt horizons (Blume and Schwertmann 1969; Nettleton

et al. 1975). The relation (r 5 0.67, P , 0.001) found between Fed and

clay supports this assumption. Moreover, the ratio of Fed/clay remained

rather constant in most horizons of all soil profiles (Table 3). Based on

results with similar trends, other authors concluded that Fed was

translocated to deeper soil layers by the process of clay illuviation (Blume

and Schwertmann 1969; Karyotis, Kosmos, and Yassoglu 1996).

Boero and Schwertmann (1989) in terra rossa soils around the world

and Durn, Ottner, and Slovenec (1999) in terra rossa in Istria (Croatia)

found a limited variation of Fe-oxide characteristics in their data set, and

the arithmetic means of the two data sets were not significantly different.

In this study, mean Fed content was lower (1.16% ¡ 0.18, Table 4)

compared to the previously mentioned studies; however, it is closer to the

values of Bech et al. (1997), who found mean Fed content of 1.51% ¡

642 C. Noulas et al.

0.20 in Spain. These results may support the conclusion of Boero and

Schwertmann (1989) that the rather low variation of selected Fe-oxide

characteristics shows red soils are formed under a specific pedogenetic

environment.

The ratio Feo/Fed (termed ‘‘active ratio’’) ranged from 0.04 to 0.34

(Table 4), and values were higher in surface horizons of most soil profiles.

This can be attributed to higher soil organic C content, which retards the

crystallization of Fe oxides (Schwertmann 1966). Comparing the Feo/Fed

values in the argillic horizons, it was observed that profiles P1, P2, and P3

exhibited values similar but comparatively lower than those of P5 and/or

P6, indicating the degree of development of the former three pedons

(Alexander 1974). The markedly higher Feo/Fed in P5 is probably

Table 3. Iron and manganese oxides and indices of soil development

Profile Horizon Fed

(g/kg)Fed/clay

(6100)

Feo

(g/kg)Feo/Fed

Fed–Feo

(g/kg)

Mnd

(g/kg)II

(Fed)aFed/Mnd

RIb

P1 Bt1 22.1 5.0 1.82 0.08 20.3 0.62 35.6 15.00Bt2 20.0 5.0 1.30 0.07 18.7 0.71 28.2 15.00C 12.6 6.4 1.00 0.08 11.6 0.56 22.5 7.50

P2 AE 6.5 3.3 0.90 0.14 5.6 0.47 13.8 2.50Bt1 11.3 2.9 1.34 0.12 10.0 0.08 0.57 141.3 11.25Bt2 9.8 2.8 0.85 0.09 9.0 0.04 245.0 7.50C 7.8 2.7 0.62 0.08 7.2 0.05 156.0 3.00

P3 AE 8.7 3.1 1.37 0.16 7.3 0.94 9.3 7.50Bt1 16.6 4.4 2.51 0.15 14.1 0.80 0.52 20.8 7.50Bt2 19.8 3.1 0.78 0.04 19.0 0.34 58.2 7.50Ck1 9.3 3.2 0.57 0.06 8.7 0.24 38.8 2.50

P4 EB 8.9 4.1 1.04 0.12 7.9 0.83 10.7 7.50Bt1 9.0 3.6 1.17 0.13 7.8 0.56 0.99 16.1 11.25Bt2 10.5 3.8 1.27 0.12 9.2 0.58 18.1 11.25BC 10.3 4.4 1.73 0.17 8.6 0.60 17.2 11.25

P5 E 7.2 6.9 2.46 0.34 4.7 0.61 11.8 2.50EB 8.0 3.8 1.81 0.23 6.2 0.63 12.7 2.50Bt1 13.3 4.2 3.18 0.24 10.1 0.63 0.54 21.1 15.00Bt2 12.7 3.6 2.64 0.21 10.1 0.60 21.2 15.00BC 12.0 4.1 2.77 0.23 9.2 0.67 17.9 15.00

P6 BE 8.0 2.3 1.88 0.24 6.1 0.34 23.5 5.00Bt1 12.5 2.8 1.96 0.16 10.5 0.12 0.64 104.2 11.25BC 11.1 3.0 1.64 0.15 9.5 0.32 34.7 11.25C 8.7 2.0 0.78 0.09 7.9 0.52 16.7 7.50

aII (Fed) 5 illuviation index of iron 5 Fed A horizon / Fed Bt horizon.bRI 5 redness index 5 (hue 6 chroma) / value.

Nature and Management of Mediterranean Rhodoxeralfs 643

connected to the size of crystalline forms of Fe oxides and the conditions

of their crystallization (Karyotis, Kosmas, and Yassoglou 1996).

Likewise, the Fed–Feo difference (Arduino et al. 1986) showed that soils

P1 and P3 are older with Fe progressively going into ‘‘less active’’ forms

(Bech et al. 1997). In the case of P2, the decreased (Fed–Feo) values could

be attributed to the low Fe content of Chorizon (Table 3). The Fed–Feo

showed an average value of 9.97 g kg21 with a minimum of 4.70 and

maximum of 20.30 g kg21 (Table 4).

Iron II ranged from 0.52 to 0.99 and was lower in the profiles P2 and

P3 than in P4 and P6. Because II is indicative for the degree of soil

development, it can be argued that soils P2 and P3 are less developed than

P4 and P6. Our results are in agreement with Beck et al.’s (1997) range of

Fe IIs. Mean RIs of Bt horizons were found in the following decreasing

order: P1 5 P5 . P4 and P6 . P2 . P3 (Table 3). Although P2 has well-

expressed characteristics of development compared to other profiles, the

influence of microclimatic soil conditions that affect both Fe oxidation

(Karyotis, Kosmas, and Yassoglou 1996) and content of organic matter

may be responsible for its lower RIs. However, the rates of redness were

moderately correlated to Fed (r 5 0.59, P , 0.002, n 5 24).

Manganese oxides (Mnd) range from 0.04 to 0.94 g kg21 (Table 4)

and decrease slightly in the argillic horizons of P2, P4, and P6 or remain

constant in P5 (Table 3). However, there was no clear trend of

distribution with depth, Haidouti et al. (2001) found similar patterns.

MacKenzie (1980) reported that higher values were usually found in soils

with high Fe and organic matter content in semiarid environments. In the

present study, higher Mnd values were observed in the surface horizons of

Table 4. Basic statistics of selected parameters (n 5 24) of the studied

Rhodoxeralfs

Parameter Meana Median Min. Max. SDb

Sand (%) 50.00 ¡ 3.63 49.70 28.80 67.80 8.60

Silt (%) 17.88 ¡ 3.03 17.70 6.70 29.40 7.18

Clay (%) 32.13 ¡ 4.72 30.75 10.40 64.50 11.19

CEC 24.08 ¡ 3.17 22.40 9.30 36.20 7.51

SOC 4.65 ¡ 1.68 3.40 0.70 16.90 3.99

Fed 11.53 ¡ 1.78 10.40 6.50 22.10 4.21

Fed/clay 3.77 ¡ 0.50 3.60 2.00 6.90 1.18

Feo 1.56 ¡ 0.31 1.36 0.57 3.18 0.73

Feo/Fed 0.15 ¡ 0.03 0.14 0.04 0.34 0.07

Fed–Feo 9.97 ¡ 1.75 9.10 4.70 20.30 4.14

Mnd 0.49 ¡ 0.11 0.57 0.04 0.94 0.25

RI 8.88 ¡ 1.86 7.50 2.50 15.00 4.41

aAverage of samples ¡ standard error of the mean at 0.05 probability level.bSD 5 standard deviation.

644 C. Noulas et al.

four pedons. As was found by other authors (Durn, Slovenec, and Covic

2001), Mn oxides were not correlated with clay content or Fed. These

results suggest that probably Mnd oxides do not take part in the co-

illuviation of clay and Fed oxides or that these are remobilized. Values of

Mno are very low (data not shown) compared to those of Mnd; therefore

Mnd content is attributed to the presence of Mn oxides and hydroxides

(Blume and Schwertmann 1969; Durn, Slovenec, and Covic 2001).

Land Use and Management

The soils that are located on back slopes or shoulders exhibit higher risk

of erosion, especially during the winter rainy period. In one case, the

argillic horizon is exposed on the surface. These soils surfaces are

generally acidic, as a result of the removal of CaCO3 and recent extensive

use of acidifying fertilizers. Farmers are strongly recommended to change

fertilization practices and to start using liming material to adjust pH up

to 6.5. Summer drought in combination to sloping terrain and the

inherent medium to low fertility classify the red allochthonous soils into

the medium-potential land-quality category (Commission of the

European Communities 1992). Rain-fed grain crops and olive and

almond groves are the common land utilization types on sloping terrains.

On terraces, cotton is preferably grown under intensive conditions in

which sprinkle irrigation is applied. Iron oxides and clay migrated into Bt

horizons, reaching their maximum content in the well-developed Bt

horizons. Their relatively limited variation reveals the specific pedoge-

netic environment in which red soils were formed. The ratio Feo/Fed in

the argillic horizons, as well as the II of Fed, indicated that among soils,

P1, P2, and P3 are less recent than the others. The influence of

microclimatic soil conditions and the organic C content are among the

main factors that affect RIs. There was no clear trend of Mnd distribution

with depth. Minimum tillage, terracing, banning of burning of plant

residues, mulching, and nonacidifying use of N-based fertilizers are

suggested as management practices to control erosion and enhance soil

fertility of rain-fed land utilization types. In the flat or slightly sloping red

soils, the following practices are recommended: rational water use to

prevent leaching of nitrates, split application of N fertilizers according to

plant demands, and incorporation of plant residues after harvesting.

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