Interpretation of Faunal (Termite) Activity Based on Micromorphic Records in Some Ferruginous Soils of Southern India

The Southern India Plateau is covered by dominantly organic matter-poor ferruginous soils derived from pre-cambrian igneous rocks. High faunal activity especially by termites is very common. Micromorphic studies of fifty (50) Kubiena size (5x7 cm) thin sections from four pedons revealed the dominance of spheroidal and ellipsoidal mineral excrements of sizes ranging from 50–250 μm. The excrements commonly occurred on clustered and welded forms, occasionally as individuals. Three stages of ageing (disintegrations) of excrements were observed, namely extreme ageing, moderate ageing and initial ageing. The excrements were composed of mostly mineral matter, clay and disrupted pedofeatures suggesting the consumption of soil material by the soil feeding termites. The faunal voids were smooth, regular or irregular and were plastered with clay and sesquioxides along the walls. They occurred as individuals or as inter-connected and rarely as intersected ones with the width ranging up to 1000 μm. The pale coloured regions suggestive of zones affected by termite activity aided in demarcating the pathways and excrement zones of termites. The tiensity of these pathways and excrement zones have been used as a criterion for understanding soil structure and porosity. Further, the visual interpretation aided by enlargement zones, viz. 1. Dominated by faunal voids and mineral excrements; 2. Dominated by groundmass and less of mineral excrements and faunal voids; 3. Dominated by S-matrix; 4. Dominated by voids. Accordingly the soil structure and porosity were categorised as: 1. High porosity and weak structure; 2. Moderate porosity and moderate structure; 3. Poor porosity and strong structure. The studies showed that macrotermes played an important role in the improvement of porosity in these soils.