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Soil organic carbon (SOC) plays a vital role in soil fertility and is important for its contributions to mitigation and adaptation to climate change. The present study was undertaken to estimate the SOC stock in soils under different land uses of Cauvery Delta zone of Tamil Nadu. Four different land uses were selected for the study viz, Forests, Agriculture, Agro-forestry and Plantations. Soil samples were collected from Madukkur and Kalathur soil series of Cauvery Delta zone for soil carbon analysis. The soil samples were fractionated into three aggregate size classes viz., macro-aggregates (250-2000µm), micro-aggregates (53-250 µm) and silt and clay sized fraction (<53 µm). At 0-30 cm depth, the forest land use stored the maximum SOC stock in the different size fractions viz. macro-sized fraction (73.0 Mg ha-1), a micro-sized fraction (76.0 Mg ha-1) and silt+clay sized fraction (77.0 Mg ha-1) in Madukkur series. Agriculture land use registered the lowest SOC stock. Among the different size fractions, silt+clay sized fraction (< 53 µm) retained the maximum SOC in all the land uses. In Kalathur series also, maximum soil organic carbon stock was recorded in forest land use. The data generated in the study will be beneficial to the user groups viz., farmers in identifying the most suitable land use for enhancing the storage of soil organic carbon thereby improving yields of crops and trees.

Plantations are efficient sequesters of carbon and can mitigate the predicted rise in atmospheric CO2 concentration and future climate change. Trees can capture atmospheric CO2 through photosynthesis and store it in biomass with a turnover time of several decades. The present investigation was undertaken to study the carbon stock in biomass of important plantation species of clonal and seedling origin in the Southern agro-climatic zone of Tamil Nadu. The existing stands of three different ages of a tree plantation were selected from within the available plantations on farmlands, and data on girth and height were recorded for all the trees. The results revealed that the total carbon stocks (537.8 Mg ha-1) was maximum under Eucalyptus clonal plantation of >6 years. Aboveground biomass was greater than belowground biomass, accounting for 79% of total biomass in Casuarina clonal plantation of > 5 years. Biomass carbon stock in Melia increased from 49.8 Mg C ha-1 in 1 to 4 years plantation to 95.5 Mg C ha-1 in >7 years old plantation. The findings explain the ability of clonal plantations of Casuarina and Eucalyptus in accumulating maximum biomass carbon stock.

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