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, [email protected] 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. REFERENCES Rhoades, J.D., 1996, Salinity: Electrical conductivity and total dissolved solids, in Methods of Soil Analysis. Part 3. Chemical Methods, pp 417 - 435. SSSA Book Ser. 5. SSSA and ASA, Madison WI. 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