Continental-scale controls on soil organic carbon across sub-Saharan Africa

Summary

This continental-scale analysis of 1601 soil samples across sub-Saharan Africa demonstrates that geochemical properties—particularly oxalate-extractable metals and exchangeable calcium—are equally important predictors of soil organic carbon as climatic variables (temperature and aridity). The relative importance of geochemical factors varies with soil weathering status and pH: highly weathered acidic soils in wet regions show stronger dependence on metal oxides, whilst alkaline and less weathered soils in drier regions depend more on exchangeable calcium. Notably, land cover and soil texture were not significant predictors at continental scale, suggesting that soil mineralogy and geochemistry represent the primary controls on SOC stabilisation across African soils—a finding that echoes patterns observed in temperate regions despite fundamental differences in soil development history.

UK applicability

The findings have limited direct applicability to UK conditions, as UK soils typically develop under temperate climates with different weathering regimes, parent materials, and land-use histories than sub-Saharan African soils. However, the methodological approach of using mixed-effects and random forest models to identify continental-scale SOC controls could inform UK soil monitoring and carbon sequestration policy, and the emphasis on geochemical factors over texture may prompt re-evaluation of SOC predictors in British soil classification systems.

Key measures

Soil organic carbon concentration; oxalate-extractable metals (aluminium and iron); exchangeable calcium; soil pH; soil texture; mean annual temperature; aridity index; land cover type

Outcomes reported

The study identified key soil properties and climate variables controlling soil organic carbon concentrations across sub-Saharan Africa using 1601 soil samples from 17 countries at two depths (0–20 and 20–50 cm). Statistical modelling revealed that geochemical properties and climate variables together explain approximately two-thirds of SOC variation across the region.

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