3.2 Soil reaction, exchangeable bases, extractable acidity, CEC
and base saturation
The increase in pH, exchangeable Ca and Mg in coffee soils has resulted
from application of liming materials in the coffee plantation. In
Chikmagalur, lime has gone down considerably, to 20 cm, exhibiting the
effect of dolomite application and the low Al concentration in
Chikmagalur in comparison to Wayanad and Idukki. This increase in soil
pH has resulted from a reduction in organic matter. Changes of soil pH,
a reduction of the litter habitat and increased anthropogenic
disturbance via site management practices add to degradation (Nair et
al., 2016). Liming of coffee plantation has corrected the strongly
acidic soil reaction. Total exchangeable bases recorded higher in the
deeper layers of coffee plantations in comparison to the forest system.
The higher content of Ca and Mg in the deeper layers of coffee
plantations is due to the leaching of Ca and Mg as a result of
management of Ca and Mg in the coffee plantations of Chikmagalur and
Wayanad. But in Idukki coffee plantation, there was no observable
difference in Ca and Mg as well as in soil pH, which has resulted from
insignificant lime or dolomite application. BaCl2-TEA
extractable acidity was higher in forest soils. This may be due to high
organic carbon content and high intensity of leaching as a result of
high rainfall (Kharche et al., 2000). Cation exchange capacity was more
in coffee soils than forest soils. In all the profiles, CEC was higher
in the surface soils due to the presence of higher organic matter and Ca
and Mg in the surface layers. The CEC decreases on moving down the
profile and lesser was the CEC recorded at deeper layers. This has
resulted from the decomposition of organic matter. Calcite and dolomite
applied to the coffee plantations leached down the profile and resulted
in higher exchangeable Ca and Mg in the deeper layers. Soil CEC is
important for maintaining soil fertility as it influences the total
quantity of nutrients available to plants at the exchange site (Yitbarek
et al., 2013). Soil CEC increased by following conversion of forest to
crop fields (McGrath et al., 2001). The application of liming materials
to neutralise the pH has served the purpose of soil conditioners which
in direct contact with soils have evolved as a technique to achieve
restoration of soil qualities upon conversion from natural forest to
cultivated ecosystem (Saturday, 2018).