Total soil organic carbon and carbon sequestration potential in Nigeria

• The study shows a large variability in SOC across various land use and agroecosystems.
• Soil type, climate, vegetation indices and terrain attributes are important predictors of SOC.
• About 6.5 Pg SOC stored in the top 1 m of soils in Nigeria.
• High SOC density found in Forests, Ferralsols and Humid forest agroecological zone.
• Findings vital for framing appropriate management regimes to increase soil carbon stocks.

This study aimed to quantify SOC stocks and potential C sequestration for Nigeria using legacy soil data. Mass preserving splines were fitted to legacy SOC and bulk density (BD) pedon data based on GlobalSoilmap soil depths. SOC concentrations (g kg−1) were predicted using Random Forest model (RFM), Cubist and Boosted regression tree (BRT). Thereafter, the soil carbon density (Mg C ha− 1) was calculated from the SOC concentration and BD (Mg m− 3). The information was combined with land use/land cover (LULC) map and agro-ecological zone (AEZ) digital maps to estimate SOC sequestration. The mean SOC concentration ranged between 4.2 and 23.7 g kg− 1 in the top 30 cm and between 2.6 and 9.2 g kg− 1 at the lower soil depth. Total SOC stock in the top 1 m was 6.5 Pg with an average density of 71.60 Mg C ha− 1. Almost half of the SOC stock was found in the 0–30 cm layer. SOC stocks decreased from the southwest to the northeast of Nigeria, and increased from Sahel to Humid forest agro-ecological zones. Restoration of the various land use types has the potential to sequester about 0.2 to 30.8 Mg C ha− 1 depending on the AEZ. The Derived Guinea Savannah presents a potential hotspot for targeted carbon sequestration projects in Nigeria. Knowledge of SOC stock and sequestration is vital for framing appropriate management regimes to increase soil carbon stocks, for C accounting and environmental monitoring purposes.