Variability of Selected Physico-chemical Properties of Soil Overlying Different Parent Materials in Odukpani, Cross River State

This research investigated variability among soil properties in soils overlying shale, sandstones and limestone parent materials. The result showed variability in percent sand, silt and clay content in both surface and subsurface soil. The texture ranged from clay, loam, sandy clay to sandy clay loam. The soils were acidic except those developed on limestone. The organic carbon contents of the soils were low to moderate. Total nitrogen was low while available phosphorus was high. In all parent materials exchangeable bases consistently decreased with geomorphic surfaces and were in the magnitude of Ca2+ > Mg2+ > K+ > Na+. The result of the study also showed that landscape position (crest, middle slope and valley bottom) significantly influences sand and clay content, available phosphorus, and exchangeable acidity (H+) and the crest had the highest sand content, middle slope had the highest clay content, valley bottom had highest available phosphorus while the crest and valley bottom had the highest exchangeable H+. Also, parent materials (shale, sandstone and limestone) significantly influences sand and clay content, pH, organic carbon, available phosphorus, exchangeable Ca and Mg, exchangeable acidity (Al and H), ECEC and BS. pH and base saturation within and across the three parent materials consistently had low variability class (CV< 15%) whereas soil texture particularly percent silt and Al+++ consistently had high variability class (CV >35%). This result suggest that uniform management practices for soil properties with high variability alongside with those having low variability in Odukpani soils can leads to failure of crops to response to such management practices and yield loses are inevitable.