Calculating charge density of clays : an improvised method

Abstract

Two benchmark Vertisols from Maharashtra, viz. Linga series (Typic Haplusterts in Nagpur district) and Pahur series (Sodic Haplusterts in Yavatmal district) of Maharashtra were chosen for the study. The fine clay fractions are dominated by smectite with small amounts of vermiculite. Reduced CECs of the fine clays were determined after the Greene-Kelly test. CEC and calculated surface charges are distributed in both the tetrahedral and octahedral layers of which the former (65%) is higher than the latter (35%). However, the proportion of octahedral CEC and charge increases (44%) with the deduction of the contribution of vermiculite and chlorite CEC from the tetrahedral (corrected) CEC. The The CEC and charge distribution exhibited fairly good relationship with some soil properties such as, fine clay, COLE, moisture retention at 1500 kPa, hydraulic conductivity and pH. The study also indicated that determination of reduced CECs from Greene-Kelley test is an effective means of measuring the octahedral and tetrahedral CECs and also for calculating the charge of soil clays. The Pahur soils could be more prone to hydroxy-interlayering owing to its higher tetrahedral charge than Linga soils. The surface area method overestimates the calculation of charge from CEC than formula weight method.