3.1 Selected morphological and physical properties of soils
The surface soils were darker in both the ecosystems which are a result of intensive decomposition of organic matter due to high temperature, intense leaching of bases due to high rainfall leaving sesqui-oxides at the surface and melanization or coating of dark colour over it and oxidative weathering in these humid tropics (Kharche et al., 2000). The increase in the clay content in the surface soils of coffee plantation in comparison to that of natural forest and the increase in clay content with depth up to the initial 100 cm in all the pedons is due to the dispersion of clay at the surface and illuviation of clay to lower layers (Kharche et al., 2000). The clay content further decreased and deeper layers recorded lesser clay content, which is due to the influence of parent material. Cultivated soils recorded higher clay content in the surface when compared to the forest ecosystem, owing to mixing of sub-surface soil layers rich in clay with surface, while making the land ready for starting of plantation. Bulk density of coffee plantation soils was comparatively more than that of forest ecosystem. However, these bulk density levels were in no way limiting for infiltration and movements of water (Nair et al., 2016). The lower bulk density at the surface is attributed to the influence of organic carbon rich surface soils, which is remaining intact in top layer with litter of forest trees, while in cultivated soils thickness of high organic carbon layer is more with little low organic carbon per cent due to mixing and intercultural operations (Nair et al., 2016).
The mean annual soil temperature was 22ᴼC or higher classifying the soils in isohyperthermic temperature regime. The soils occur in the ustic soil moisture regime characterising it under ustic sub-group. In ustic soil moisture regime, when the soil temperature is >22ᴼC, the soil moisture control section is dry in some or all parts for 90 or cumulative days in normal years. All the soils belong to order Ultisols and Humults sub order, which is assigned owing to very high levels of soil organic carbon in the top 50 cm (> 0.9 %). Humults are freely drained humus rich soils coming under order Ultisols.
Chikmagalur forest and coffee soils were very deep, moderately acid, dark brown in colour, low cation exchange capacity and base saturation and were classified as Kanhaplohumults and Kandihumults under Ustic subgroup respectively. Soils of Wayanad forest and coffee plantation were very deep, strongly acidic in sub-surface and slightly acidic in surface and were classified as Kandihumults and Haplohumults under Ustic sub-group respectively. Idukki soils were deep, strongly acidic with low cation exchange capacity and base saturation with dark brown in the surface to red or dark reddish brown colour in the deeper layers and were classified as Kandihumults and Palehumults under Ustic sub-group indicating the soil moisture control section is dry in some or all parts for 90 or cumulative days in normal years.