Carbon Storage in Soil Fractions and Carbon Dynamics in Shaded Perennial Agroforestry Systems.

Soil particle size and land management practices are known to have considerable influence on carbon (C) storage and subsequent sequestration in soils, but such information is lacking for shaded perennial coffee systems in the Western Ghats of Karnataka, India. Shaded perennial agroforestry systems contain relatively high quantities of soil carbon (C) resulting from continuous deposition of plant residues; however, the extent to which the C is sequestered in soil will depend on the extent of physical protection of soil organic C (SOC). This study aims to quantify the amounts of soil C stored at various depths to 100 cm under agroforestry systems of varying shade conditions. Soils were fractionated into three size classes (<53, 53–250, and 250–2000 mm), and C stored in them and in the whole (non-fractionated) soil were determined. In terms of C stock in three soil fraction-size classes, differences among land-use systems were most pronounced for macro-size (250 – 2000 µm), followed by micro-size (53 – 250µm) and silt + clay (< 53 µm) fractions.

To validate our findings, we developed a simple Carbon model based on the classic DAYCENT model. The model uses a monthly time step and can simulate the dynamics of soil organic matter over long time periods. It was used to simulate the impact of soil carbon fractions and increasing depth on soil carbon dynamics. The model was validated by comparing the simulated impact of cultivation on soil organic matter C with observed data from our studies as well as varying agroforestry sites within tropical and sub-tropical climate around the world.