Soil Carbon Storage in Silvopastoral Systems and a Treeless Pasture in Northwestern Spain

Soil particle size and land management practices are known to have considerable infl uence on carbon (C) storage in soils, but such information is lacking for silvopastoral systems in Spain. Th is study quantifi ed the amounts of soil C stored at various depths to 100 cm under silvopastoral plots of radiata pine (Pinus radiata D. Don) and birch (Betula pendula Roth) in comparison to treeless pasture in Galicia, Spain. Soils were fractionated into three size classes (<53, 53–250, and 250–2000 μm), and C stored in them and in the whole (nonfractionated) soil was determined. Overall, the C stock to 1 m ranged from 80.9 to 176.9 Mg ha−1 in these soils. Up to 1 m depth, 78.82% of C was found in the 0- to 25-cm soil depth, with 12.9, 4.92, and 3.36% in the 25- to 50-, 50- to 75-, and 75- to 100-cm depths, respectively. Soils under birch at 0 to 25 cm stored more C in the 250- to 2000-μm size class as compared with those under radiata pine; at that depth, pasture had more C than pine silvopasture in the smaller soil fractions (<53 and 53–250 μm). In the 75- to 100-cm depth, there was signifi cantly more storage of C in the 250- to 2000-μm fraction in both silvopastures as compared with the pasture. Th e higher storage of soil C in larger fraction size in lower soil depths of silvopasture suggests that planting of trees into traditional agricultural landscapes will promote longer-term storage of C in the soil.