Mineralogical, geochemical and nutrient analysis of soils from
Omalos polje -plateau, Western Crete.
N. Lydakis – Simantiris
Laboratory of Environmental Chemistry and Biochemical Processes, Department of
Natural Resources and the Environment, Technological and Educational Institute of
Crete.
D. Pentari, V. Perdikatsis, E. Manutsoglu, D. Moraetis, and Ch. Apostolaki
Laboratory of Geochemistry, Organic Geochemistry and Organic Petrography.
Department of Mineral Resources Engineering. Technical University of Crete. 73100
Chania, vperdik@mred.tuc.gr
ABSTRACT
Preliminary results of a mineralogical, geochemical and nutrient analysis of soil samples
collected from Omalos polje-plateau are presented. This study is part of a project
concerning the relationship of lithology and mineralogy characteristics of soils of
different geological origin from the island of Crete with their chemical composition, and
more specifically with their ionic nutrients content. The results presented in this work
show a relatively good correlation of the mineralogy and the bulk content of the soils
examined with the available nutrients in soil solution.
1. INTRODUCTION
It is well known that soil constitutes a
practically no renewable, natural
resource, with a key role for the
environment and of major importance
for Greece since the economy of the
country is largely based on agriculture.
The pedological properties(i.e. mineral
content, pH, electrical conductivity) that
are critical for the utilization of soil are
governed
by
the
petrological/
mineralogical characteristics and the
geological origin of the soil system. In
order to understand deeply the nature of
soil as well as its interaction with the
environment
a
multidisciplinary
approach, focusing on environmental
sustainable utilization of soil is required.
Within this context the study and
correlation of mineralogical and
geochemical characteristics with nutrient
content of the soils is of great
importance.
So far a significant number of papers
have been published reporting studies
concerning either the mineralogy/
geochemistry and geological setting of
soil samples (i.e Egli, 1993, Nakos,
1984, Weinmann, 1964) or their nutrient
fertility. Especially for Omalos area
there is an extensive study of the ecology
as related to pedological properties (Egli,
1993). However, the correlation of the
above-mentioned characteristics has not
been examined thoroughly. The work
presented in this paper provides
preliminary data in the direction of
helping to fill this gap. For this aim soil
samples have been collected and
investigated for their mineralogical
characteristics as well as for their
content in available nutrients with the
objective to assess the correlation of
these characteristics.
2. GEOLOGICAL OUTLINE.
The island of Crete is located north of
the Hellenic trench. The geological
framework consists largely of nappes of
contrasting
lithologies
and
metamorphism that were stacked
southwards during an Oligocene to early
Miocene N-S compression. Most of the
whole nappe stack of continental Greece
is recognised in Crete. It has however a
reduced thickness and more important
shortening. The nappes are stacked from
top to bottom, i.e. from the most internal
to external units in the following order:
Asterousia nappe, Miamou nappe, Arvi
nappe, Pindos-Ethia nappe, Tripolitza
nappe, Phyllite nappe and Trypali nappe.
The Plattenkalk Group represents the
lowermost known tectonic unit beneath
the nappe pile of Crete and their
formation has been involved in the
tectonometamorphic process during the
Oligocene-Miocene.
The sampling area is situated in the west
part of “Leuka Ori” mountains and its
geomorphology is a typical plateau. The
Omalos plateau lies on the fault
separating the “Trypali” nappe from the
underlying limestones. The area consists
of three geological units i) Neocene and
Quaternary formations ii) Trypali unit
iii) Plattenkalk group. Figure 1 presents
the geological outline of the area. The
plateau consists mainly of marl and
conglomerates which lie on the
“Trypali”
limestones.
The
rock
formations around the Omalos plateau
are mainly part of the Trypali unit and
less of the Plattenkalk group.
(Manutsoglu
Spyridonos,
Soujon,
Jacobshagen, 2001).
3. MATERIALS AND METHODS
3.1. Sample collection and storage.
Sampling was performed using a special
soil auger, designed for all soil types.
Samples were collected from sites
chosen according to three strategic
guidelines i) soils that have not been
cultivated ii) sites where different soil
horizons were apparent iii) sites where
the mineralogical variation was apparent
due to different parent materials. Nine
representative samples (No 1-9) were
collected. Samples were transferred to
the laboratory, crashed, dried at 37ºC for
48 h, and sieved with 2 mm sieves.
Finally, the samples were put in plastic
containers and stored at room
temperature until use. Table 1 shows the
exact position of the sampling sites in
Omalos polje-plateau.
3.2.
Mineralogical
analyses.
Mineralogical
components
were
determined by x-ray diffraction XRD
using a Siemens D500 XRD instrument
Allouvial
Trypali Unit
Plattenkalk Group
Figure 1 Location of the Omalos polje-plateau and geological outline of the area.
(Geological map after Tataris and Christodoulou 1969)
on the sample fraction below 63μm. This
fraction was attained by separation with
an Atteberg cylinder. The data obtained
at 35 kV and 35 mA, with a graphite
monochromator, using CuKa radiation.
A 0.03° scanning step and 2-s scanning
time per step was used for the range 3 to
50°. The qualitative evaluation of the
data was done with the Software Diffrac
Plus from SOCABIM. The quantitative
analysis was carried out by the Rietveld
Method.
3.3. Chemical analyses. pH: Deionized
water was added to soil samples up to a
ratio 1:2 soil : water and mixed. The
mixture was left for 10 min, then it was
mixed again and after 5 min the pH
value of the supernatant was measured
with a calibrated pH meter. Electrical
conductivity: A saturated soil – water
paste was prepared and left for 4-5 h in
order for the readily soluble salts to
dissolve. Then, the saturated soil paste
was transferred to a Büchner vacuum
filter and the filtrate was collected.
Electrical conductivity was measured on
the filtrate with a calibrated conductivity
meter.
The electrical conductivity
values were reduced to those at 25ºC
(Rhoades, 1996). Available phosphorus:
for available P determination, extraction
of phosphorus by NaHCO3 0,5 N, pH 8.5
was performed and, after filtration of the
extractant, the Olsen method was applied
(Watanabe and Olsen, 1965). Available
K, Mg: potassium and magnesium were
extracted from soil samples by
CH3COONH4 1 M, and after filtration
and proper dilution their concentration
was determined by atomic absorption
(Perkin Elmer AA100). Soluble Ca: For
soluble calcium determination, atomic
absorption was performed on the soil –
water filtrate (Rhoades, 1996). Available
micronutrients: Fe, Cu, Mn, and Zn were
extracted by the DTPA method,
(Lindsay and Norvell, 1978), and atomic
absorption spectroscopy was performed
for the determination of their
concentration.
3.4.
Major
elements
total
concentrations. The total concentrations
of major elements were determined by
X-ray florescence on the sample fraction
below 2mm. The chemical analysis was
obtained
by
energy
dispersive
spectroscopy (EDS Model: S2 Ranger).
The measurement obtained in 40 kV
with a Al filter (500 μm) for the heavier
elements (Fe, Mn, Ti, Ca, K) and in 20
kV for the lighter elements (P, Si, Al,
Mg, Na). The measurement time was set
to 100 sec for each group of elements
(heavy, light).
3.5. Grain size analysis. The content of
sand, clay and silt of the samples was
determined by Bouyoucos method
(Bouyoucos, 1962).
4. RESULTS AND DISCUSSION
The mineralogical and chemical analysis
results are presented in table 2 and 3
respectively. The minerals determined
were mainly quartz, chlorite/kaolinite,
illite and less calcite. Kaolinite and
chlorite are presented in the same
column due to line overlapping in the
XRD spectra. Further thermal treatment
of the sample and subsequent XRD
analysis is required in order to reveal the
percentage of kaolinite and chlorite.
Table 2 shows a variation in
mineralogical composition for the 9
samples examined in this study.
Variation is detected for sample 7 where
the quartz concentration is 11.7%
compared to other samples where the
concentration
is
above
40%
approximately. Another significant
observation is the increase in
concentration of clay minerals in sample
7 compared to the rest of the samples. In
sample 7 there is high concentration of
illite and samples 1, 2, 3, exhibit also
increased concentration of illite. In
addition sample 2 exhibits calcite
concentration of approximately 2%
whereas the other samples have
concentrations lower than 0.1%.
Table 1. Sampling sites coordinates
Coordinates
(N)
(E)
(ALT)
1
35.20.536'
023.53.911'
1032
NW
2
35.20.536'
023.53.911'
1032
NW
3
35.20.536'
023.53.911'
1032
NW
4
35.20.415'
023.53.678'
1040
NW
5
35.20.412'
023.53.682'
1038
NW
6
35.20.529'
023.53.576'
1037
W
7
35.20.484'
023.53.471'
1044
W
8
35.20.548'
023.53.577'
1068
SW
9
35.20.554'
023.53.749'
1069
SW
The above mineralogical analysis is
verified by the bulk chemical analysis
presented in table 3. The presence of
high iron oxide concentration in sample
7 is related to the high concentration of
illite. Magnesium concentration is
increased in sample 7 whereas in other
samples was not detectable. Also, the
calcium oxide concentration in sample 2
is in accordance with the mineralogical
analysis.
Figure 2 presents the particle size
distribution for the samples. Samples 3,
Table 3.XRF-EDS Chemical analysis
Sample
1
2
3
4
5
6
7
8
9
Na2O
(%)
<0.4
<0.4
0,99
1,55
0,00
1,44
<0.4
<0.4
0,48
MgO
(%)
<0.5
<0.5
<0.5
<0.5
<0.5
<0.5
4,26
<0.5
<0.5
K2O
(%)
1,05
1,99
1,07
0,70
0,79
0,41
4,20
0,22
0,63
CaO
(%)
0,54
5,47
0,73
0,31
0,25
0,35
0,49
0,14
0,28
TiO2
(%)
0,33
0,42
0,39
0,25
0,31
0,44
0,72
0,20
0,24
6, 9, and 5, 4, are characterized loamy
and silt loamy, respectively. Samples 1,
8 and 2 are in the area of sandy loam and
sandy clay loam. The sample 7 consists
of clay and this is in accordance with the
high concentration of clay minerals in
the sample. Table 4 presents the
nutrients analyses results available in the
soil solution. Significantly higher is the
content of the potassium available in soil
solution for the samples 1, 2, 3 and 7.
There is significant correlation between
the extractable potassium and the
potassium concentration from total
chemical analysis (XRF).
Also,
magnesium concentration is significantly
high in soil solution for the sample 7
where in total analysis detected high
magnesium concentration whereas in
other samples magnesium was not
present.
On the
contrary iron
concentration in soil solution exhibits no
correlation with the total iron analysis
Table 2. Mineralogical analysis and
semi-quantification results
1
2
3
4
5
6
7
8
9
Calcite
%
*
1.97
*
*
0.1
0.12
*
0.1
*
Kaolinite/
Chlorite %
15.1
18.0
15.3
13.0
33.0
51.50
17.7
10.30
13.20
Illite
%
12.06
25.7
21.01
2.89
4.50
9.97
71.00
9.55
10.30
Quartz
%
72.9
54.4
63.7
84.0
62.0
38.4
11.7
80.00
76.50
*not detected
MnO
(%)
0,17
0,23
0,23
0,08
0,02
0,14
0,07
0,13
0,17
Fe2O3
(%)
3,18
4,19
3,89
2,31
3,56
3,71
9,19
2,07
2,33
Al2O3
(%)
6,13
10,07
8,10
4,93
7,25
9,80
21,03
3,04
5,01
SiO2
(%)
87,93
75,16
83,68
89,28
86,72
83,36
57,72
93,95
90,14
P2O5
(%)
<0.08
<0.08
<0.08
<0.08
<0.08
<0.08
<0.08
<0.08
<0.08
LOI
0,49
1,49
1,07
0,78
1,27
0,52
2,15
0,41
0,89
Figure 2. Grain size distribution.
5. CONCLUSIONS
The results presented in this paper
comprise the first set of data of an
ongoing project in our laboratories
concerning
the
interrelation
of
mineralogical
and
geochemical
properties of soils originating from
different parent material with the
nutrients available in soil solution. Such
information is significant for the
understanding of available nutrients in
plants according to mineralogy of the
soil and the parent material of the soil
formation.
It is expected that this
interrelation analysis will have a
significant impact on the protection of
the environment, since it will help to
prevent the use of excessive chemical
fertilizers. Further investigation of the
clays present in the soil will offer
valuable insight of the physical
phenomena governs the nutrient
availability in plants.
Table 4 Concentrations of nutrients available in soil solution (in ppm)
Sample
K
Mg
Cu
Fe
Zn
1
78,50
71,30
0,85
4,69
0,51
2
80,00
37,90
0,74
3,13
0,50
3
60,83
33,17
0,57
3,02
0,54
4
26,97
16,93
0,52
4,03
0,23
5
34,43
47,87
0,74
9,67
0,21
6
49,90
53,13
0,75
3,32
0,15
7
68,73
281,33
0,29
2,14
0,20
8
25,83
13,33
0,14
5,22
0,08
9
23,23
23,47
0,22
3,74
0,11
Mn
8,66
17,21
25,75
8,14
1,61
4,20
1,30
12,28
13,01
P
2,86
4,72
7,08
6,88
2,37
2,18
2,37
1,59
4,04
pH
6,95
8,4
8,01
4,96
5,11
7,32
6,4
5,11
5,18
This Work was carried out in the frame of EPEAK II (Education and Initial Vocational
Training, PYTHAGORAS II, Hellenic Ministry of National Education and Religious
Affairs. The authors thank for the economic support.
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