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Modification of Vertisol properties in relation to charge characteristics of smectites

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Title Modification of Vertisol properties in relation to charge characteristics of smectites
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Creator Ray, S.K., Chandran, P., Bhattacharyya, T. and Durge, S.L.
 
Subject Vertisol, charge, characteristics, smectites
 
Description Not Available
It has been observed that Vertisols exhibit different morphological, physical and chemical characteristics in the surface (0-50 cm) and subsurface (50-100 cm) horizons. Preliminary perusal of data indicates that toal clay remains within 67-72% while the finer fractions of clay increases from 32% in the surface to 55% in the subsurface. Although some soil characteristics such as moist consistency could be understood by higher concentration of fine clay in the subsurface, yet many other soil parameters could perhaps be explained better with detailed information on the quality of smectites which dominates in these soils.
A benchmark Vertisol from Pune (Nimone) district of Maharashtra was selected for the study. CEC before and after Greene-Kelley test and XRD analysis were done with the fine clay fractions from all the horizons.
The CEC of the fine clays varied from 78 to 95 cmol (p+) kg-1 within the profile and the reduced CEC (obtained by treating the sample with Li and heating) varied from 24 to 35 cmol(p+) kg-1. The reduced CEC is the difference between the total CEC and the CEC decreased due to retention of Li at octahedral sites. Thus the reduced CEC represents the CEC due to the tetrahedral charge of the minerals, which decreases down the profile.
Assuming the hydroxy-interlayering as minimum at the lowermost horizon (118-150 cm), it is observed that first 53cm of these soils is hydroxy-interlayered to the tune of 38-46%. It has been reported that the hydroxy-interlayering is more in the surface horizons due to exposure to stronger weathering conditions. Logically, therefore, the degree of hydroxy-interlayering will decrease down the depth.
Since charges are balanced over shortest possible distance (Pauling, 1960), it is understood that the positive charge of the hydroxy-interlayers will be neutralized by the negative charges of the tetrahedral sites. Our observation indicates that out of the total tetrahedral charge of these smectites, 38 to 46% charge is already balanced by the process of hydroxy-interlayering.The reduced CEC data indicate that the relative proportion of tetrahedral and octahedral charge varies from 25 to 38% and 62-75%, respectively. It is also observed that out of 38% tetrahedral charge in the surface layer about 46% is neutralized by hydroxy-interlayering.
Hydroxy-interlayering causes neutralization of negative charges of clay which reduces nutrient holding capacity and increases HC. The reduction of overall charge also decreases the shrink-swell potentials as evidenced by lower COLE values. Interestingly the depth at which hydroxy-interlayering is found to be minimum corresponds to the depth of first occurrence of slickensides.
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Date 2020-06-30T14:12:05Z
2020-06-30T14:12:05Z
2002-11-11
 
Type Presentation
 
Identifier Ray, S.K., Chandran, P., Bhattacharyya, T. and Durge, S.L. (2002). Modification of Vertisol properties in relation to charge characteristics of smectites. ISSS National Seminar and 67th Annual Convention, November 11-15, 2002, Jabalpur, Madhya Pradesh (Abstract), 227-228.
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http://krishi.icar.gov.in/jspui/handle/123456789/37734
 
Language English
 
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Publisher Not Available