Monday, November 13, 2006

Soil Carbon Sequestration and Stabilization in Tree-based Pasture Systems.

Solomon Haile1, Vimala Nair1, and Ramachandran P. Nair2. (1) Univ of Florida, 288 Corry Vlg Apt 23, Gainesville, FL 32603, (2) Univ of Florida, 118 Newins-Ziegler, PO Box 110410, SFRC, IFAS, Gainesville, FL 32611-0410

Compared to most agricultural systems, tree-based land-use systems such as silvopasture that integrate trees in pasture production systems are likely to enhance soil carbon (C) sequestration in deeper zones of the soil profile. The total soil C at six depths (0 – 5, 5 – 15, 15 – 30, 30 – 50, 50 – 75, and 75 – 125cm) were determined in a silvopasture of slash pine (Pinus elliottii) + bahiagrass (Paspalum notatum), and on an adjacent treeless bahiagrass pastures at two sites, representative of Spodosols and Ultisols in Florida. The C contents within three fraction-size classes (250 – 2000, 53 – 250 and <53µm) of each soil profile were determined.  Using stable C isotope signatures, the plant sources (C3 vs. C4 plant) of C fractions were determined and traced at both sites. Compared with the treeless pasture, the Spodosol profile between trees in a row in the silvopasture contained more C in the fraction <53µm at and below the spodic horizon (40cm deep). In both soil types, the C3 plant (slash pine) contributed more C in the smallest soil fraction (<53µm) than the C4 plant (bahiagrass) at all soil depths, particularly at the lower depth. The results support the hypothesis that under similar ecological settings, silvopastoral systems retain more stable C fraction in the soil profile than under treeless pasture.