Soil Carbon Storage in Shaded Perennial Agroforestry Systems in Relation to Overstory Tree Cover.

Shade-tolerant tropical perennial species are commonly grown under tall shade trees. Economic benefits have traditionally been the sole factor in assessing the value of such systems; their ecosystem services like soil carbon sequestration have seldom been quantified. We assessed soil C stored at various soil depths (0–10, 10–30, 30–60, and 60–100 cm) in five land-use systems in Koppa (12° 54´ N, 75° 04´ E), Karnataka, India. The systems were coffee (Coffea arabica) under the shade of planted Grevillea robusta (grevillea) trees, coffee under a mixture of shade trees, tea (Camellia sinensis) under the shade of grevillea, an agricultural land under common tropical annuals, and a native moist deciduous forest. From each system, four replicated composite soil samples were collected for each depth class. Soil C in the whole soil and three soil fractions, separated by wet sieving (250–2000 µm, 53–250 µm, and <53 µm), were determined. The SOC stock values (Mg C ha^-1) to one-meter depth were 177.4 under forest and 150.51 under coffee under grevillea. The lowest stocks were under agricultural land (116.4). Carbon stored (Mg C ha^-1) within the silt and clay fraction (<53 µm) up to 1m depth were highest for coffee under grevillea (34.53). Considering that C stored in this soil fraction is more stable than that in other fractions, shaded perennial agroforestry systems, especially coffee and tea under grevillea, seem to increase long-term storage of soil carbon. This ecosystem service merits deserving recognition.