Conclusion

The findings from the study confirm the view that changes have taken place in the soils of the southern forest-savanna transition zone. The decline in the soil pH and plant nutrients with continuous cultivation is caused by increased erosive losses associated with lowered organic matter in the soils. There is a possibility of an extension of the zone of depletion into lower soil horizons. It is, therefore, necessary in future to sample the entire solum if changes in the concentrations of the soil organic C and plant nutrients with continuous cultivation are to be described adequately. Information such as total solum depth, horizon thickness and bulk density would be required to evaluate the total organic matter budgets under each vegetation cover. According to Tiessen et al. (1982), the incorporation of values for horizon thickness into such data gives a measure for the total amounts of organic matter lost from a soil due to the combined effects of mineralization and erosion processes.

The decline in soil fertility in the zone could be controlled through the application of suitable fertilizers or through growing soil improving crops such as legumes in suitable rotations. Finally, agroforestry methods may be an im portent option to be considered as a means of halting the threat to soil fertility losses in the zone.