Wednesday, November 7, 2007
249-4

Soil Carbon Sequestration under Agroforestry Systems in the West African Sahel.

Asako Takimoto, University of Florida, 118 Newins-Ziegler Hall, PO Box 110410, School of Forest Resources and Conservation, Gainesville, FL 32611, Ramachandran Nair, 118 N-Z Hall, PO Box 100410, University of Florida, University of Florida, School of Forest Resources & Conservation, Gainesville, FL 32611-0410, and Vimala Nair, PO Box 110510, University of Florida, Soil and Water Science Dept., 106 Newell Hall, Gainesville, FL 32611-0510.

In recent years, carbon (C) sequestration potential of agroforestry systems has attracted attention following Kyoto Protocol's recognition of agroforestry as a greenhouse-gas-mitigation strategy. Our knowledge on this topic from the arid and semiarid regions such as the West African Sahel is very limited. To address this problem, a study was undertaken in the Ségou region of Mali (annual temperature: 29°C; annual rainfall: 300 – 700 mm in 60 to 90 days; soils: Haplustalfs, loamy sand, low in fertility) on five land-use systems in farmers’ fields [two traditional parkland systems with Faidherbia albida and Vitellaria paradoxa as the dominant tree species, two improved agroforestry systems (live fence and fodder bank), and a so-called abandoned land]. Biomass C stock was estimated by allometric equations. Soil samples collected from three depths (0 – 10, 10 – 40, and 40 – 100 cm) were fractionated (wet sieving) into three particle size classes (250 – 2000, 53 – 250, and <53 µm) and their C contents determined. Using 13C natural abundance, the plant sources (C3 vs. C4 plant) of C fractions were determined (major crops in the study region are C4, while trees are C3). Biomass C stock ranged from 0.7 to 54.0 Mg C/ha, and total C stock (biomass C + soil C, 0 – 100 cm depth) from 28.7 to 87.3 Mg C/ha. Traditional parkland agroforestry systems had larger C stock than the improved systems, but they seemed to have only limited potential for sequestering additional C; the improved systems showed more potential for C sequestration. The abandoned land that had little aboveground biomass C contained the largest soil C stock (56.2 Mg C ha-1: 0 – 100 cm), possibly an effect of land-use change. The other four systems were not different in soil C stock. The data show that the introduction of trees contributes to significant increase of C in topsoil, which will increase the protected C in deeper soil in the long term. Compared with treeless systems, agroforestry systems seem to have higher potential for soil C sequestration; but longer-term studies are needed to get conclusive results.

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