Abstract

                                The work was carried out with different parent materials to identify various clay materials in Reniguntal mandal of Chittoor district, Andhra Pradesh. The soils had pH 6.2 to 8.96, clay 3.74 to 46.58 % and CEC 2.16 to 43.63 cmol (p + ) kg -1 . In general, surface horizon had relatively higher organic carbon and decreased with depth. Soils were low in available nitrogen and phosphorus, low to medium in available potassium and high in available sulphur. Seven representative pedons were selected after surveying the areas for the study of clay minerals. The mineralogical and chemical characteristics of soils developed from granite-gneiss and calcareous murrum and alluvium parent materials. The clay film invariably exhibited the characteristic peaks of illite and kaolinite. Semi-quantitative estimates of clay fractions based on relative areas under corresponding peaks indicated that all the pedons dominated by illite and kaolinite followed by Feldspars. Quartz is present in traces. However, use and management of these soils for agricultural production require an understanding of their clay mineralogy.

Key words : Clay mineralogy, parent materials, illite, kaolinite, quartz, feldspars