Soil Carbon Sequestration Potential of Different Agricultural Management Systems in the Forest-Savanna Transition Zone of Nigeria

This study quantifies soil organic carbon sequestration potential under different agricultural management systems in the forest-savanna transition zone of Nigeria, spanning parts of Kwara, Kogi, and Edo States. The forest-savanna transition zone hosts a rich diversity of farming systems from intensive annual cropping to agroforestry, and its soils have significant carbon sequestration potential if managed appropriately. Quantifying the carbon balance of different systems is essential for understanding their role in climate change mitigation and for developing carbon credit mechanisms that can incentivise soil carbon restoration. This study establishes a 3-year soil carbon monitoring network on 24 farms representing six management systems: continuous maize monoculture, maize-legume rotation, Mucuna green manure system, cocoa agroforestry, parkland agroforestry, and forest fallow. Soil organic carbon is measured at 0 to 10, 10 to 20, and 20 to 40 centimetre depths annually using the dry combustion method. Carbon inputs from above-ground and below-ground biomass are quantified. Net ecosystem carbon balance is computed using soil respiration measurements. Findings reveal that parkland agroforestry sequesters an average of 1.42 tonnes of carbon per hectare per year, the highest of all systems. Continuous maize monoculture shows net soil carbon loss of 0.38 tonnes per hectare per year. Cocoa agroforestry and green manure systems show intermediate positive sequestration rates. The study contributes original carbon balance data for the transition zone and recommends agroforestry integration as the highest-priority management change for carbon sequestration in the zone.

Keywords: soil carbon sequestration, forest-savanna transition, agroforestry, carbon balance, Nigeria.