Chemical and morphological composition of Kankar nodules in soils of the Vindahyan region of Mirzapur, India

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CHEMICAL AND MORPHOLOGICAL COMPOSITION OF KANKAR NODULES IN SOILS OF THE VINDHYAN REGION OF MIRZAPUR, INDIA

L. SINGH"k and S. SINGH

Faculty o f Agriculture, Banaras Hindu University, Varanasi (India) (Received February 2, 1971) (Resubmitted January 25, 1972)

ABSTRACT Singh, L. and Singh, S., 1972. Chemical and morphological composition of Kankar nodules in soils of the Vindhyan region of Mirzapur, India. Geoderma, 7: 269-276. The shape, size and smoothness of Kankar nodules (concretions of lime) are somewhat dependent on the texture of the soils. The colour is controlled by the hematite and limonite, which are the sources for iron and manganese. The calcium content in Kankar and surrounding soil matrix varied from 25.6 to 38.64 and 0.73 to 5.60% as CaO, respectively. The corresponding figures for magnesium contents were 2.42 to 5.33 and 0.87 to 1.45% as MgO. The iron content in Kankar was higher than in the surrounding soil matrix and the reverse is true for manganese. Aluminium in Kankar did not show def'mite relationship with A1 of soil matrix. Phosphorus and potash content of Kankar were lower than the respective soils. Sodium in both Kankar and soil was found to be in equal range. Petrological study of different Kankar samples showed a similar mineralogical composition. A visual relationship was noted between the mineralogical compositions of Kankar and fine sand fractions in respective surrounding soil materials. INTRODUCTION The occurrence of Kankar nodules, of varying shape, size and colour, in the profiles is the characteristic feature of I n d o Gangetic alluvium, especially the "bhangar" (older alluvium) soils. The depth of Kankar horizons varies widely even in places of close proximity. Most investigators have suggested that Kankar nodules are found at the depth of rain-water penetration. Since Kankar is formed by segregation and redeposition of calcium carbonate and other materials from soils, the nature of the surrounding soil materials would greatly affect its shape, size, colour, physical and chemical characteristics. This is a study of the morphological and chemical properties of Kankar nodules and their relationship with the surrounding soil materials of the Vindhyan region. SrPresent address: Department of Soils, Haryana Agricultural University, Hissar, India.

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MATERIALS AND METHODS Nine Kankar and twenty five soil samples were collected from five soil profiles of the Vindhyan region of Mirzapur district (23o52 , and 25°15' latitude and 82°70 ' and 83°33 ' longitude). The depth of Kankar occurrence in the profiles was measured during sampling. Colours of the Kankar powder and the surrounding soil material were judged by using a Munsell colour chart. Soil texture was determined by the international pipette method. The methods described by Piper (1966) were used for chemical analyses of both Kankar and soil samples. The HCl-extracts of Kankar (10 g) and soil (20 g) samples were prepared and analysed for Ca, Mg, P, K and A1 as oxides. Total iron and manganese in the HC1extract were determined colorimetrically using orthophenonthroline and potassium periodate, respectively, as colour developers (Jackson, 1960). Organic carbon in the Kankar powder (10 g) and soil (1 g) was estimated by the wet-digestion method of Walkley and Black (1934). Soil pH of a 1:2.5 soil-water suspension was measured by a Beckman pH meter. For petrological studies, thin slides of Kankar were prepared as described below, and examined under a petrological microscope. A piece of Kankar of about 2 cm 2 size was washed thoroughly and one of its surfaces made smooth. The opposite surface was rubbed with emery flour and water on a cast-iron plate and then on a smooth brass-plate after polishing with finest emery flour and water until a thin section was obtained. It was washed with water and cooked with Canada balsam in a dish at 150°-180°C. The cooked section was gently placed in Canada balsam fluid on a warm glass slide (7.5 × 2.5 X 0.25 cm). After gentle tapping, the section was covered with a cover slip. The slide was dried in air after removing the ,superfluous balsam. RESULTS AND DISCUSSION The data pertaining to depth of Kankar occurrence, the colours of Kankar powder and soil, texture of soil and other characteristics of Kankar are given in Table I. Kankar nodules were found in a depth range of 18-150 cm. Presence of Kankar in the B-horizon of a regur (deep black soil) profile (Tamhane, 1950) and at the base of Indo-Gangetic alluvium profile (Agarwal and Mukherji, 1951) has been noted. The colour of the Kankar powder varied from white to pink and was related to that of the soil matrix. Similar observations were made by Singh and Lal (1946). Agarwal et al. (1953) reported the occurrence of murrum (hydrated iron concretions), iron concretions and Kankar in red, brown and black soils, respectively, of the Vindhyan region of Mirzapur. The shape, size and smoothness of Kankar nodules seems closely related to soil texture. Kankar nodules found in loam to clay loam had relatively smoother surfaces than those in sandy loam to loam. Singh and Lal (1946) noted that a fine-textured soil has round Kankar nodules having smooth surfaces, whereas a sandy soil contains nodules of irregular shape and size.

COMPOSITION OF KANKAR NODULES, VINDHYAN REGION

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Analytical data on the chemical composition of Kankar nodules and respective soils are presented in Table II. The pH's of soil and Kankar do not show any apparent relationship. The organic carbon in Kankar was lower than in the respective soil matrix. This is in agreement with the finding of Cherepanova (1959) who reported a lower organic-matter content in calcareous concretions than in the surrounding soil materials. The HCl-insoluble fractions in Kankar and surrounding soil materials ranged from 21.20 to 37.30% and from 59.50 to 82.28%, respectively. A similar observation was made by Singh and Lal (1946). The quantity of calcium in Kankar was positively related with that in the surrounding soil materials although not to a significant extent. However, it indicates that Ca-rich soil produced Ca-rich Kankar, which corresponds with past reports (Princep, 1831 ; Harper, 1957; Chmielowiec, 1960; Kung and Chen, 1963; Wells, 1965). The magnesium content in Kankar was higher in almost all the samples than that in the surrounding soil materials. Iron in the Kankar was less than in the soil, which indicates that the deposition of iron during Kankar formation was low. There was not any regular trend of distribution of aluminium in the Kankar or surrounding soil materials. The amounts of manganese in Kankar and in soil ranged from 0.076 to 0.228% and from 0.015 to 0.061%, respectively. The amount of phosphorus in Kankar was lower than in the respective surrounding soil materials. The potash content in Kankar and soil indicates that the potassium of soil was less deposited in the Kankar during its formation. The amounts of sodium in Kankar and the surrounding soil materials was almost in the same range. The mineralogical composition of Kankar and fine sand fractions of the respective soils are described in Table III. Microphotographs of thin-sections of Kankar nodules were prepared for study. An example of these microphotographs is given in Fig.1. I(2) Kankar: Had fine- to medium-grained texture and contained predominantly calcite and colourless quartz showing extinction at various angles. Muscovite was also noted in appreciable amounts. Hematite was observed at certain places in association with the quartz minerals. A comparison of the mineralogical compositions of fine sand fractions and Kankar indicates that only few minerals in Kankar were deposited from the soil matrix (Table III). I(5) Kankar: Minerals were the same as in the I(2) but the texture was medium- to coarse-grained and quartz showed extinction angles. The angular quartz was present in a scattered fashion, surrounded by calcite minerals. II(4) Kankar: Texture was fine-to medium-grained and the minerals, in order of abundance, were calcite, quartz, hematite, muscovite and limonite. Quartz pieces were smaller and surrounded by fine-grained calcite. I1(5) Kankar: Texture was medium- to coarse-grained. The nodules contained calcite, quartz, hematite, muscovite and limonite. At certain places, hematite is firmly attached to quartz and surrounded and cemented by calcite grains. Perelman (1951) reported that in calcareous concentrations, quartz with attached iron and cemented by calcite is common in the desert soils of Central Asia. III(3) Kankar: Texture was medium- to coarse-grained and contained calcite. The

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Fig.1. Kankar type II(5). x 200 colour was reddish-yellow under the microscope. III(4) Kankar: This had medium- to fine-grained texture. The amounts of quartz and hematite were low but calcite was abundant and widely distributed throughout the section. III(5) Kankar: The properties of this Kankar were largely identical with those of III(4). IV(2) Kankar: Texture was fine-grained. This had abundant calcite but less quartz, muscovite, limonite and magnetite. V(2) Kankar: Texture was fine- to medium-grained and contained calcite, quartz, muscovite, hematite and magnetite minerals. Calcite surrounded the quartz and showed twinkling under the microscope. ACKNOWLEDGEMENT The senior author is grateful to the Council of Scientific and Industrial Research, New Delhi for the award of a fellowship during the course of this investigation.

REFERENCES Agarwal, R.R. and Mukherji, S.K., 1951. Gangetic alluvium of India: Pedo-chemical characters of the genetic soil types of Gorakhpur district in United Provinces. Soil Sci., 72: 21-32. Agarwal, R.R., Mukherji, S.K. and Verma, R.N., 1953. The soils of the Vindhyan Plateau in the Mirzapur district of U.P. lndian J. Agric. Sci., 23:113-120. Cherepanova, M.N., 1959. Chemical composition of calcareous concretions and their genesis. Dokl. Mosk. Sel'skokhoz. Akad., 42: 153-158. Chmielowiec, G., 1960. Calcareous concretions in the loess of Poland. Ann. Univ. Mariae Curie. Sklodowska, Lublin.Polonia, Sect. B, 15: 39-49.

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Harper, W.G., 1957. Morphology and genesis of calcisols. Soil Sci. SOc. Am. Proc., 21: 420-424. Jackson, M.L., 1960. Soil Chemical Analysis. Prentice Hall, London. Kung, T.T. and Chen, T.C., 1963. Characteristics and formation of calcified paddy soil in south China. Acta Pedol. Sin., 11: 92-98. Perelman, A., 1951. Calcareous concretions of the Karakums and Kizilkums. Dokl. Akad. Nauk., 78: 1001-1004. Piper, C.S., 1966. Soil and Plant Analysis. Hans Publishers, Bombay. Princep, J., 1831. Chemical analysis of Ghazipur Kankar. Glean, Sci., 3: 278. Singh, D. and Lal, G., 1946. Kankar composition as an index of the nature of soil profile. Indian J. Agric. Sci., 16: 328-342. Tamhane, R.V., 1950. Regur soils of India. Trans. Int. Congr. Soil Sci., 4th. 3: 131-134. Walkley, A. and Black, T.A., 1934. An examination of the Degtjareff method for determining soil organic matter and a proposed modification of the chromic acid titration method. Soil Sci., 37: 29-38. Wells, C.B., 1965. The formation of calcium carbonate concretions. Proc. Int. Congr. Exp. Pedol., 11th, Nottingham, 1964, pp.165-172.