Sand Mineralogy of Soils Representing Three Agroecological Subregions of Peninsular India

Six representative pedons were examined in the hot subhumid to humid, hot humid and in hot semi-arid eco-regions of central and south Sahyadri regions, Coastal plains of Kerala and Karnataka and in Deccan plateau of Karnataka, respectively to understand the weathering stages in different soils. The sand mineralogical studies reveal that the unstable minerals in the heavy sand fraction of soils from the humid tropical region are not completely weathered probably because of the ferruginous surficial coating which blocks the site of weathering. The abundance of unstable minerals viz., pyroxene, hornblende and biotite in the heavy sand fraction are derived from the nearby granitic gneisses and schists upon weathering. The soils supporting arecanut plantation are highly weathered followed by the soils supporting rubber and coffee. Soils of the coastal plains cultivated for coconut are least weathered.