ABSTRACT
The relative contributions of clay and organic matter to the cation exchange capacity of soils have been of great interest to many researchers. Organic matter. as a critical component of the soil. plays. significant roles which far exceed its quantitative distribution in the soil. It is regarded as the major contributor of CEC in weathered soils because of its several functional groups such as R-COO-. R-C=O. R-COH and R-SI I that deprotonate and leave net negative charges on the humus. The objective of this study was to assess the contribution of SOM to CEC soils in Nigeria. Data on CEC. OM. pH and clay collected from 191 soil samples based on literature reports across the country. Data was analyzed using SIGMAPLOT STATISTICAL SOFTWARE:_ There was no significant relationship yet seen CEC anJ pH measured in either H20 or dilute CaCl2 solution. CEC correlated significantly with clay: and explained 55% the variation in CFC of the soils. The organic carbon (OC) has the highest correlation with CEC and explained 72% of the variation of the CEC. The predictive empirical model for estimating CEC from OC is CEC = 5.81 + 5.23 (OC), r2=0.72. A unit change in OC increases CEC by 5.23 mmol kg-1 in contrast to the small increase in CEC by 0.4 mmol kg-1 per unit change in clay content. On a unit change hasis. OC contribution ll) C[C was thirteen times greater than clay. Therefore land management practices that increase and maintain the organic matter contents must be adapted to sustain the fertility of soils in Nigeria
