Comparative Assessment of Soil Carbon Stocks Under Different Land Use Types in Borno State

Soil organic carbon stocks in the dryland ecosystems of Borno State are highly sensitive to land use change, with potential implications for both climate regulation and soil productivity, yet comparative data across land use types under the specific conditions of the Lake Chad basin region are limited. This study compares soil organic carbon stocks under five land use categories: natural woodland, protected forest reserve, community agroforestry, continuous cropland, and severely degraded bare land in three Local Government Areas of Borno State. Soil samples were collected at three depths (0-10 cm, 10-30 cm, and 30-50 cm) from four randomly selected plots per land use type, yielding 300 soil samples in total. Organic carbon was determined using the Walkley-Black wet oxidation method, with bulk density measured for volumetric stock calculation. Stepwise regression identified soil physical variables most strongly associated with organic carbon variation. Natural woodland soils showed the highest carbon stocks at all three sampled depths, averaging 28.4 tonnes per hectare in the top 50 centimetres. Protected forest reserve soils were comparable to woodland. Continuous cropland showed a 52% reduction in topsoil carbon relative to woodland, while degraded bare land showed a 79% reduction. Agroforestry soils occupied an intermediate position, significantly higher than continuous cropland. Organic matter contribution from tree leaf litter was identified as the critical differentiating mechanism. The study recommends tree retention and agroforestry promotion as priority soil carbon conservation strategies under the Borno State Agricultural Transformation Agenda. Keywords: soil organic carbon, land use types, Borno State, carbon stocks, agroforestry