Contribution of organic matter and clay to the cation exchange capacity of soils in the savanna zone of Nigeria

The cation exchange capacities (CEC) of surface and subsurface soils of Afaka, Mokwa, Nimbia and Sanga River forest reserves in the savanna region of Nigeria were determined. The CEC was statistically partioned into organic matter and clay components using linear multiple regression analysis. Standard partial regression coefficients indicate that the cation exchange properties of the surface soils were mostly associated with organic matter. Between 50 and 83 per cent of the variation in the CEC values could be attributed to organic matter content. The exchange capacities of organic matter in the four reserves were calculated to be in the range 282 to 322 me/100g while those of clay were 7 to 18 me/100g. Except in Nimbia forest reserve, the contribution of clay to the CEC of surface soils was nonsignificant. In the subsoils both organic matter and clay made significant contributions to the CEC. Multiple correlation coefficients (R) of organic matter and clay with CEC in the subsoils were? 0.86, 0.66, 0.05 and 0.76 for Afaka, Mokwa, Nimbia and Sanga River respectively. Comparison of their standard partial regression coefficients (b) showed that clay was more important in predicting the CEC of the subsoils.