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).