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Not AvailableHydroxy-interlayerig (HI) in soil clay smectites of Vertisols in Peninsular India is a common phenomenon. Presence of small to moderate amounts of HI also affects the properties of soils. Earlier the view was that pH higher than 7.5 in soils may be the reason for HI. However, this explanation did not work in soil clay smectites of sodic Vertisols of Anantapur district of Andhra Pradesh and Purna valley of Maharashtra as the smectites in these areas are not hydroxy-interlayered. This demanded investigation for possible source and reason of HI in the soil clay smectites. Clay smectites of some Vertisols from Maharashtra (Takarkheda, Seloo and Saikhindi series) had small (about 3-5% in Seloo and Saikhindi) to moderate (about 5-15% in Takarkheda) HI. Mineralogical analysis by X-ray diffraction of soil clays indicated presence of HI, that were identified by (1) the nature of the graphs of K-saturated samples heated from 110° to 550°C; the peak at 1.0 nm was greatly reinforced with tailing on its low angle sides. In absence of chlorite, the 1.4 nm peak indicated hydroxy-interlayered smectite (HIS), (2) intensity of Ca-treated samples were higher than the Ca-EG treated samples which indicated presence of HIS and (3) persistence of 1.4 nm peak (after Greene-Kelly test) confirmed presence of HIS. The hydroxy-interlayered materials in hydroxy-interlayered smectities (HIS) are positively charged hydroxy-cations such as [Al3(OH)4]5+, [Al6(OH)15]3+, [Fe3(OH)6]3+, [Mg2Al(OH)6]+, etc. The positively charged hydroxy-cations are usually formed under acid weathering conditions in a humid tropical climate where substantial amount of Fe3+, Al3+, Mg2+ are available. Hence, the transformation of smectite to HIS by inclusion of hydroxy-cations would require acid weathering under humid tropical environment. In contrast, the study area where the Vertisols are formed have a semi-arid climate and a moderately to strongly alkaline conditions. This suggests that the presence of HIS in the study area representing semi-arid climate and having alkaline conditions is unlikely to favour the formation of HIS. Thus, the reactions involving hydroxy-interlayering is not a contemporary pedogenic process under semi-arid climatic conditions. The HIS which has been produced in the humid tropical area may have been transported through rivers and streams. After this depositional episode in wetter climate, soils became calcareous due to the change of climate to semi-arid. Thus, the HIS remained as a signature of climate change phenomenon.Not Availabl

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Not AvailableShrink-swell (Vertisols and their intergrades) soils cover an extensive area especially in Peninsular India with smectites as the dominant mineral. It was felt necessary to find out the species of smectites for better management of these soils. Hence, two benchmark Vertisols namely Seloo from Wardha and Saikhindi from Ahmadnagar districts of Maharashtra were chosen for the study. High resolution mineralogical analysis employed through X ray diffraction (XRD) techniques of the silt, total clay and fine clay fractions of both the pedons were carried out along with Greene-Kelly test with only fine clays. Silt (50-2 μm), total clay (<2 μm) and fine clay (<0.2 μm) fractions are dominated by smectite in both the soils; the smectites content increased gradually with decreasing size fraction. The fine clay fractions are mostly composed of smectite with small amounts of vermiculite and traces of chlorite, kaolin and feldspar. Greene-Kelly test indicated that both Seloo and Saikhindi soil fine clays are dominated by beidellite/nontronite over montmorillonite. The Seloo fine clay smectite is composed of 18-26 per cent and 74-82 per cent montmorillonite and beidellite/nontronite, respectively, and for Saikhindi it is composed of 32-41 per cent and 59-68 per cent for montmorillonite and beidellite/nontronite, respectively. However, these fine clay smectites are of low charge dioctahedral nature and therefore may not have any K selectivity. This property appears to have implications in K management of shrink-swell soils of Deccan basalt areas.Not Availabl

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Not AvailableDetermination of layer charge of soil clay smectites of the Peninsular India (PI) by alkylammonium method (Lagaly and Weiss, 1969) is generally encountered with some problems related to the inherent properties of smectites. The charges of these smectites are generally higher and the values are seldom closer to that of pure bentonite (Ray et al., 2003; Deshmukh, 2009). This is attributed to differential nature of smectites of Peninsular India. Detail study of the clay smectites indicate that hydroxy-interlayering (HI) is a common phenomenon (Pal and Deshpande, 1987, Bhattacharyya, et al., 1993, Deshmukh et al., 2009) in shrink-swell soils of PI. The presence of HI in smectites affects the determination of actual layer charge by alkylammonium method and the values obtained are found to be overestimated. The present study envisages to determine the layer charge of soil clay smectites before and after removal of HI. The EDTA method for the removal of HI from soil clay smectites has been used here for evaluation of the method. Two benchmark Vertisols from Maharashtra namely Seloo from Wardha and Saikhindi from Ahmednagar districts were chosen for the study. Fine clays were separated from the soils, characterized by XRD and were treated with alkylammonium hydrochlorides of various chain lengths before and after removal of HI.The fine clays contain dominant amount of smectite with small amounts of vermiculite and traces of chlorite, kaolin and feldspar. The smectites are partially chloritzed as evidenced by broadening towards the low angle side of 1.0 nm peak in K-saturated sample after subsequent heating to 550°C which is common in Vertisols. Greene-Kelly test showed the presence of both beidellitic/nontronitic and montmorillonite; where the former dominated over the latter. The weighted average layer charge by alkylammonium method for Seloo and Saikhindi fine clays are 0.450 and 0.432 mol(-)/(Si,Al)4O10(OH)2, respectively. The layer charge is highest at the surface and decreases down the depth for Seloo whereas for Saikhindi it showed irregular trend. After EDTA treatment and removal of HI, the semi-quantitative estimate showed a decrease in chlorite and increase in smectite values. This was also reflected in the values of weighted average layer charges (0.366 and 0.361 mol(-)/(Si,Al)4O10(OH)2 for Seloo and Saikhindi clays, respectively) which decreased from the original values without EDTA treatment. This also suggests that EDTA is an effective extractant to remove HI from soil clay smectites. The removal of HI by EDTA method resulted in the decrease in layer charge compared to the original fine clays. This can thus help to resolve the problem of determining the actual layer charge of hydroxy-interlayered smectites by alkylammonium method.Not Availabl