Contribution of trees to carbon storage in soils of silvopastoral systems in Florida, USA

Authors

  • SOLOMON G. HAILE,

    1. Center for Subtropical Agroforestry, School of Forest Resources and Conservation, PO Box 110410, University of Florida, Gainesville, FL 32611, USA,
    2. Soil and Water Science Department, PO Box 110510; Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611, USA
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  • VIMALA D. NAIR,

    1. Soil and Water Science Department, PO Box 110510; Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611, USA
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  • P. K. RAMACHANDRAN NAIR

    1. Center for Subtropical Agroforestry, School of Forest Resources and Conservation, PO Box 110410, University of Florida, Gainesville, FL 32611, USA,
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Vimala D. Nair, tel. +352 392 1804, fax +352 392 3399, e-mail: vdn@ufl.edu

Abstract

Silvopastoral systems that integrate trees in pasture production systems are likely to enhance soil carbon (C) storage in lower soil layers due to the presence of deep tree roots. To quantify the relative soil C contribution from trees (C3 plants) and warm season grasses (C4 plants) in silvopastoral systems, soil samples were collected and analyzed from silvopastures of slash pine (Pinus elliottii)+bahiagrass (Paspalum notatum), and adjacent open pasture (OP), at six depths down to 125 cm, at four sites representing two major soil orders (Spodosols and Ultisols) of Florida. The plant sources of C in whole (nonfractionated) and three soil fraction sizes (250–2000, 53–250, and <53 μm) were traced using stable C isotope signatures. The silvopasture sites contained higher amounts of C3-derived soil organic carbon (SOC) compared with OP sites, at all soil depths. Slash pine trees (C3 plants) seemed to have contributed more C in the silt+clay-sized (<53 μm) fractions than bahiagrass (C4 plants), particularly deeper in the soil profile. Spodosols sites contained more C in the <53 μm fraction at and below the spodic horizon (occurring between 15 and 50 cm) in silvopasture compared with OP. The results indicate that most of SOC in deeper soil profiles and the relatively stable <53 μm C fraction were derived from tree components (C3 plants) in all the sites, suggesting that the tree-based pasture system has greater potential to store more stable C in the soil compared with the treeless system.

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