SOIL ORGANIC CARBON (SOC) CHANGES UNDER BIODIESEL PLANTATIONS (PONGAMIA PINNATA)
Soil organic carbon (SOC) represents an important C sink in the lifecycle C balances of biofuels and strongly influences soil quality. One potentially significant impact of growing Pongamia pinnata in drylands will be the Sequestration or release of carbon (C) in soil and large amount of organic matter added through litter fall and improve the soil health. We assembled and analysed on carbon sequestration and soil properties estimates of SOC change from 2003 to 2013 following conversion of natural land to Pongamia plantations. We estimated net change in SOC relative to a control (open plot) since establishment year (2003). Soil samples were collected from all treatments of Pongamia plantations at two different depths: 0-20 cm and 20-40 cm Under Tree Canopy (UTC), Under Litter Trap (ULT) and Uncultivated Area (Open Plot). Soil samples were air dried ground and sieved to 1mm and analysed for total carbon content by combustion method using the LECO CR-412 carbon analyser. The average contribution of SOC by different treatments at 0-20cm depth was UTC (13.37 ton/ha), ULT (5.18 ton/ha), Open area (4.75 ton /ha).and whereas at 20-40cm the values of SOC by UTC, ULT and open area were 7.76 tons/ha, 3.76 tons/ha and 3.69 tons/ha, respectively. Excavation of total root system was done manually and carried out within one week of the above ground sampling under dry soil conditions and subsequently washed with water to remove the adhering soil. The below ground dry biomass was 18.63 tons/ha. The litter traps made of 1 x 1m nylon fishing net fitted to stakes at 1 m above the ground was used to trap the litter, were placed under the canopy of each tree per treatment (various spacing). The results showed that the total quantity of litter dry biomass produced in a year was 8.35 ton/ha, 7.49 ton/ha, 7.2 ton/ha and 6.79 ton/ha under tree spacings of 5mx5m, 6mx4m, 6mx6m and 8mx6m respectively. However, the dry carbon biomass under tree spacings of 5mx5m, 6mx4m, 6mx6m and 8mx6m was 3.93t/ha,3.52t/ha,3.39t/ha, and 3.19 t/ha, respectively.