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.