CLAY MINERALOGY INFLUENCE ON THE PHYSICAL AND CHEMICAL PROPERTIES OF VERTISOLS FROM ROMANIA

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1 Factori şi Procese Pedogenetice din Zona Temperată 7 S. nouă (28) CLAY MINERALOGY INFLUENCE ON THE PHYSICAL AND CHEMICAL PROPERTIES OF VERTISOLS FROM ROMANIA INTRODUCTION Victoria Mocanu, C. Craciun, M. Eftene, Sorina Dumitru, Valentina Cotet National Research-Development Institute for Soil Science, Agrochemistry and Environment Protection-Bucharest Abstract The mineralogical investigation of the 33 profiles of vertisol from Romania indicated that there are two principal geographical zones with vertisols (West and South) which present some quantitative mineralogical differences at the colloidal level. In spite of the fact that in all investigated profiles, the quantitative mineralogical composition of the clay fraction (below 2μ) was the same, (smectite, illite and kaolinite) the vertisols from the western zone show a higher content of smectite (montmorillonite) and a lower content of illite in comparison with vertisols from southern zone. The correlations between some physical indices of soil and smectite quantity indicated that an increase of soil smectite content determines an increase of bulk density and compaction degree, concomitantly with a decrease of total porosity and air porosity. The established relationships between some chemical indices and mineralogical parameters indicated that cation exchange properties and reaction of these soils appear more closely related to the quality (mineralogical composition) than to the quantity of clay fraction. The empirical relationships established between physical and chemical indices of vertisols and mineralogical parameters suggest that in some cases, considered favorable, the clay mineral information could allow some predictions on the physical and chemical properties, in spite of the fact that such of predictions have a limited value from quantitative point of view. Key words: vertosol, clay minerals The physical and chemical properties of soils are strongly influenced by the soil constituents which have high specific surface or highly reactive surfaces. Since high specific surface is associated with small particle size, the colloidal fraction (below 2 µm) of the soil is the dominant factor in influencing certain properties of the soil. The usefulness of clay mineral information depends upon how closely clay minerals influence physical and chemical properties of the soils and upon our methodological posibilities to make evident and to estimate this influence. The goal of this paper is to present some aspects referring to the mineralogical composition of the clay fraction (below 2μ) from vertisols of Romania, and the influence of the clay minerals on some physical and chemical properties involved in the fertility of these soils. 17

2 Victoria Mocanu et.al. / Factori şi Procese Pedogenetice din Zona Temperată 7 S. nouă (28) MATERIAL AND METHODS A number of 33 soil profiles classified as vertisols were selected for this study. The location of the sampling sites is given in Figure 1. The clay fraction below 2μ was separated from the soil by gravity sedimentation using Na OH 4% as dispersing agent (Craciun &Gata, 1986). For the X ray analysis oriented specimens were separated by depositing 3 ml of clay suspension into a glass slide. All clay fraction samples were subjected to three types of X-ray examination (K-saturated-, Ca saturated- and glycolated Ca saturated sample). The mineralogical composition of the clay fraction was estimated by X-ray diffraction using the intensities of the characteristic basal reflections (1) of the identified clay minerals (Gâţă et al. 1981). The X-ray diffraction patterns were carried out with a DRON-2, difractometer using Ni-filtered CuKα radiation. The physical and chemical analyses were carried out by the usual methods. The influence of the clay minerals on the physical and chemical properties of these soils has been studied using the statistical correlation between physical and chemical indices, on once hand and mineralogical parameters (the contents of the principal clay minerals and clay content of the on the other hand. Fig. nr. 1 Emplacement of the investigated soil profiles 18

3 Victoria Mocanu et.al. / Factori şi Procese Pedogenetice din Zona Temperată 7 S. nouă (28) Fig. 2 X-ray diffraction patterns of the clay fraction (<2μm) separated from the surface horizon of the Balaci vertisol (values in nm) A= K-saturated sample; B= Ca-saturated sample; C= Ethylen glycol treated Ca-sample RESULTS AND DISCUSSION From the qualitative point of view, there are no mineralogical differences between the investigated soil profiles, the identified clay minerals in all Romanian vertisols being smectite, illite and kaolinite (Fig. 2). Generally, the results of mineralogical analyses indicate the existence of two groups of soil profiles occurring in the distinct geographical zones. The quantitative mineralogical differences between the two groups of profiles refer to the ratio of the principal components of the clay (Table 1). 19

4 Victoria Mocanu et.al. / Factori şi Procese Pedogenetice din Zona Temperată 7 S. nouă (28) Table 1 THE MINERALOGICAL COMPOSITION (AVERAGE VALUE) OF THE CLAY FROM STUDIED VERTISOLS AS FUNCTION OF GEOGRAPHICAL ZONE Geographical zone Mineralogical composition of the clay(%) Smectite Illite Kaolinite Smectite/Illite ratio Whole country Western zone Southern zone The smectite /illite ratio of the vertisols located in the Western part of Romania show higher values (2.84) comparing to the vertisols located in Southern part of Romania (1.69). In the case of some vertisols from Southern part of Romania the attempts to correlate the mineralogical parameters with the indices which express certain physical and chemical properties point out the influence of the clay quality and quantity on these properties. Since the physical and chemical indices do not correlate preferentially linear or parabolic with mineralogical parameters in the figures are given only the linear correlation results. The correlation attempts of the physical and chemical indices with the parameters which express the quantity and quality of the clay fraction, show a similarity between the influence of the clay content and soil smectite content (Figure 3,4). The relationship of the clay parameters with the studied physical and chemical indices is direct except the relation with total porosity which is inverse. CONCLUSIONS - The identified clay minerals in the vertisols of Romania are, in order of occurence, smectite (montmorillonite), illite and kaolinite. - There are in Romania two main areas occupied by vertisols which are different from the quantitative mineralogical point of view. - The established relation between physical and chemical indices on the side, and mineralogical parameters on the other side, show that in comparison with physical properties of vertisols those chemical appear more closely related to clay quality than clay quantity. These relations could be considered take an attempts of clay influence quantification on the soil properties. 11

5 Victoria Mocanu et.al. / Factori şi Procese Pedogenetice din Zona Temperată 7 S. nouă (28) y =,9x + 1,4 R =,459** 2 y =,11x + 1,168 R =,447** Bulk density (g/cm3) 1,5 1, DA Linear (DA) Bulk density (g/cm3) 1,5 1, DA Linear (DA) 6 y =,358x + 6,91 R =,451** 4 y =,859x 6,68 R =,513*** Total porosity (% v/v) PT Linear (PT) Degree of compactation index (% v/v) GT Linear (GT) Degree of compaction index (% v/v) y =,668x 14,38 R =,52*** GT Linear (GT) Degree of compactation index (% v/v) y =,859x 6,68 R =,513*** GT Linear (GT) Fig. 3 Relationships of some physical parameters with soil clay content and soil smectite content respectively, for some vertisols from Sothern part of Romania 111

6 Victoria Mocanu et.al. / Factori şi Procese Pedogenetice din Zona Temperată 7 S. nouă (28) Cation exchange capacity (me/1 g y =,368x + 12,79 R =,518** Cation exchange capacity (me/1 g y =,532x + 15,53 R =,594*** Total exchangeable bases (me/1 g y =,393x + 7,92 R =,52** Total exchangeable bases (me/1g y =,617x + 9,572 R =,626*** Fig. 4 Relationships of chemical parameters (exchange properties) with clay content and soil smectite content respectively, for some vertisols from Southern part of Romania. REFERENCES CANARACHE A., (199) Fizica solurilor agricole. Ed. Ceres, Bucureşti. CRĂCIUN C., 1998, The clay minerals in vertisols of Romania. Implication in soil physical and chemical properties. Ştiinţa Solului nr. 1-2, p CRĂCIUN C., LATIŞ L., DULVARA EUFROSINA, ZOTA MARILENA (1996 b) Influenţa mineralelor argiloase asupra unor însuşiri de bază ale solului: Proprietăţile chimice. Analele I.C.P.A., v LII, p CRĂCIUN C., 1993, Caracteristicile termice ale mineralelor smectitice. Ştiinta Solului nr. 1-2, p CRĂCIUN C., GÂŢĂ G. (1986) Stabilirea compoziţiei mineralogice a fracţiunii coloidale anorganice din soluri. Cap. 18 din Metode de analiză chimică a solului, p

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