الفهرس 
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Abstract
As mentioned earlier the purpose of this investigation is to study the mineralogical composition of the sand and clay fractions of some soils having different characteristics to reveal the effect or relation between clay mineralogy and some chemical characteristics i.e. cation exchange capacity (CEC). The different soils selected for this study were chosen from different areas have apparently different parent material or sediments. Five locations were selected i.e. Shalakan Farm, which located sudden Delta and formed essentially from Nile sediments, the second location is a private farm at El-Khatatba area at 84 kilo Cairo-Alexandria desert road, where vast sand sheets area where largest project of land reclamation for agricultural extension is carried out by mostly private sectors. The third site is at West Nubaria (Bunger El-Sokker area) where projects for reclaiming calcareous soils to represent cultivated calcareous soils. The forth is an area located at kilo 114 south Alexandria-Marsa Matruh desert road to represent the highly calcareous soils (deposits). The fifth is taken from the Northern part of Kafr El-Sheikh Governorate from cultivated and non-cultivated area object to the black sand deposit. A number of profiles and sites were taken from different locations to represent the different soils with a total number of 33 samples. The collected samples were air dried and prepared for different physical, chemical, mineralogical and spectral analyses.
Physical analyses included color, mechanical analysis and saturation percentages, while chemical analyses included EC, pH, soluble cations and anions, OM, CaCO3 and free iron oxides. Mineralogical analyses included, separation of the fine sand and clay fractions, identification of fine sand mineralogical composition using the polarizing microscope, identification of minerals of the clay fraction subjecting the studied samples for the different pretreatments. The mineralogical studies also included determination of the cation exchange capacities of the clay samples before and after removal of different constituents such as free iron oxides, amorphous materials (SiO2+ Al2O3), and CaCO3. While the spectral study included measuring the spectral reflectance from all studied soil samples using FR-ASD FieldSpec3 spectroradiometer from spectral range between 350-2500 nm.
The obtained results from this investigation can be summarized as follows:
1. Physical characteristics:
The studied samples have different texture varying from very heavy texture (clay and derivatives) Shalakan Farm soils to (sandy and derivatives) the Northern part of Kafr El-Sheikh Governorate. Color differs from dark (Shalakan Farm samples) to salt and pepper appearance in the Northern part of Kafr El-Sheikh Governorate soil according to content and type of clay and sand minerals. Saturation percentage also varied from 10 % to 66 % going with the amount of clay present.
2. Concerning chemical characteristics:
Studied samples have content of total soluble salts varying from non-saline (EC= 0.44 dS/m in the Northern part of Kafr El-Sheikh Governorate samples) to strongly saline (EC= 183 dS/m in El-Khatatba samples). And pH from neutral (7.11) at El-Khatatba samples to slightly alkaline (8.01) at the North Western Coast samples and alkaline 8.5 at the Northern part of Kafr El-Sheikh Governorate samples associated with different distribution for soluble cations and anions.
CaCO3 content, also varies greatly from traces (0.15 % at the Northern part of Kafr El-Sheikh Governorate samples) to highly calcareous ≈80.8 % i.e. soils of the North Western Coast.
3. Mineralogical characteristics:
Important results were obtained concerning the mineralogy of sand fraction (size from 0.25-0.063 mm). Shalakan Farm soils were not examined due to their low content of sand.
Sand fractions (0.25-0.063 mm) of El-Khatatba soils: light minerals are in relatively descending order-quartz dominated the light minerals followed by chert, plagioclase, microcline and gypsum. While the heavy fraction dominated by (also in relatively descending order) opaques then zircon, pyroxenes, tourmaline, garnet, staurolite, amphiboles, rutile and kyanite.
While the light minerals of the North Western Coast (highly calcareous) were dominated by quartz and/or calcite with small amount or traces of feldspars. Their heavy minerals were almost the same as those of El-Khatatba except presence of traces monazite mineral.
Regarding light mineral fraction of the Northern part of Kafr El-Sheikh Governorate site, quartz was the only mineral detected in the light minerals of their sand fraction. Heavy minerals are composed of the same combination of minerals found in other location except present of monazite as the second dominant mineral in their heavy fraction.
In most of the studied sites the total distribution of resistant minerals, metastable and less resistant minerals have the same trend. As total distribution of resistant minerals (rutile, zircon and tourmaline) are higher than that of the less resistant minerals (pyroxene and amphiboles) indicating that the studied areas are highly weathered and are subjected to severe soil forming processes. As the present environmental condition all over those areas is dry and no pedogenic diagnostic features were found, the dominance of the resistant minerals in the fine sand fractions of the studied area is believed to be inherited from parent sediments from past history.
Concerning the mineralogical composition of clay separated from different locations it is found that clays of Shalakan Farm and the Northern part of Kafr El-Sheikh Governorate are dominated by smectite and or/ kaolinite or quartz then feldspars and mica. Clay fraction of the North Western Coast is dominated by calcite and kaolinite followed by quartz and mica. El-Khatatba clays has the following minerals in descending order: quartz> palygorskite > kaolinite > smectite > feldspars. While West Nubaria clays were dominated by kaolinite, palygorskite, feldspars and quartz.
4. The cation exchange capacity.
Cation exchange capacity is one of the most important chemical characteristics of soils as it affect fertility and nutrient status of soils.
CEC values of the studied clays separated from different locations varied greatly with kind of minerals predominant in the clay fraction being as high as 58.05 or 46.78 meq/100g clay in the samples of Shalakan Farm and the Northern part of Kafr El-Sheikh Goverorate and 9.32 meq/100g clay in El-Khatatba clay. Smectite and/or kaolinite minerals dominate the clay of the first location while quartz and/or palygorskite and kaolinite dominated in the second location.
CEC values are affected by the type and content of some soil constituents, i.e. free iron oxides, amorphous materials and CaCO3.
Results of this investigation revealed that CaCO3 removal decreased the CEC (West Nubaria ”14.4 %” and the North Western Coast sample ”55.9” %), indicating that CaCO3 in the clay fraction (micrite) is an active constituents and have positive effect in CEC values of the calcareous soils.
Removal of the other constituents (free iron oxides and amorphous materials ”SiO2+Al2O3”) increased greatly the CEC of all studied clay samples. The increase % in CEC values after removal of free iron oxides range from 0.6 % in the Northern part of Kafr El- Sheikh Governorate clay to 69.1 % in the North Western Coast clays. While after removal of amorphous materials the increase in CEC values range from 46.7 % in the Northern part of Kafr El- Sheikh Governorate clay to 34.7 % in Shalakan clays.
5. Spectral reflectance measurements showed that:
1. Soils dominated by calcite or quartz and palygorskite (in sand and clay fractions) e.g. the North Western Coast, West Nubaria and El-Khatatba samples reflect more light than soils dominated by smectite (in the clay fraction) e.g. Shalakan Farm and the Northern part of Kafr El-Sheikh Governorate samples.
2. Reflectance of all studied soils increased by increasing wavelength from 350 to 2500 nm.
3. Reflectance of the North Western Coast soils were much higher than reflectance of Shalakan Farm soils due to differences in color, CaCO3, clay and organic matter contents.
4. Reflectance decrease as clay and organic matter increased.
5. The best relationship was found between average soil reflectance and soil clay content with high correlation coefficient (R2 =0.722).
6. The correlation coefficient between average soil reflectance and other constituents e.g. calcium carbonate, free iron oxides and organic matter were 0.3459, 0.2647 and 0.0055, respectively.
7. The spectral behavior is a useful tool to some extent in detection of clay content in the studied soils.
8. The number of soil samples used in this study would have been increased to reach more reliable conclusion concerning quantitative estimation for the effect of calcium carbonate, organic matter and free iron oxides on soil reflectance.