Emerging ecological trends in West Africa: implications on soil organic matter and other soil quality indicators

Aims In West Africa, savannas are changing to either forest islands or arable lands arising from anthropogenic interference with the natural ecosystem. This study aimed at quantifying the trade-offs of this land use conversion on major soil quality indicators. Methods We evaluated soil organic matter (SOM) and other soil quality indicators such as macro- and micronutrients (including the absence of some hazardous trace metals) using standard methodologies across 11 settlements in Burkina Faso, Ghana, and Nigeria. The degree of soil quality improvement/degradation and soil quality were assessed using empirical models. Results The effects of savanna conversion were manifold and varied depending on the type of land use change, soil depth, and soil quality indicator. In savanna-forests, there was a substantial rise in SOM (37%—794%) and exchangeable cations (15% to 800%) and changes in SOM in the topsoil quadrupled that of the subsoil. A general loss in SOM (1% -74%) and soil macro-and micronutrients occurred under savanna-arable lands. Potassium, calcium and magnesium increased by ≥ 12%, ≥ 15% and 27% respectively while increases in Mn and Zn were 37% and ≥ 250% in the forests over the savannas. Trace quantities of Pb were detected which were below the contamination threshold. About 63% forest islands, 18% arable land, and 9% savannas had SQI % ≥ 50. Conclusion In marginal lands, land use conversion to forest islands presents great potential for improving soil fertility and overall ecosystem health as shown in the high organic matter and improved soil quality.