Carbon sequestration in paddy soil as influenced by organic and inorganic amendments

Rice plants mediate carbon (C) emission from paddy soils but also absorb it as carbon dioxide (CO2) during photosynthesis. This means that net C emission could vary depending on rice cultivation techniques, which is not well documented in Asian regions. In the present investigation, the effect of different C sources on major greenhouse gas (GHG) fluxes and their relationships between C inputs and outputs were established by using closed static chamber technique. Total methane (CH4), nitrous oxide (N2O) and CO2 emissions were significantly higher with integrated plant nutrient system (IPNS) based fertilization with cowdung (CD), poultry manure (PM) and vermicompost (VC) than chemical fertilizer alone. Net ecosystem C budget (NECB) was positive with CD-IPNS (52-54 kg C ha(-1)), PM-IPNS (62-64 kg C ha(-1)) and VC-IPNS (53-56 kg C ha(-1)) but negative with chemical fertilization (-7 to -8 kg C ha(-1)). In control and chemical fertilizer treatments, net CO2 sequestration was negative (-602 and -87 kg CO2 ha(-1)), but organic amendments showed positive CO2 sequestration that varied from 68 to 94 kg CO2 ha(-1) during the study periods. Organic amendment significantly improved CO2 capturing capacity by about 17-22 gm kg(-1) grain yield compared to chemical fertilization (-24 to -25 gm kg(-1)). Rice yield also enhanced by about 14-23% with organic amendments compared to chemical fertilizer treatment. In conclusion, use of organic C sources would be very valuable practice to increase net CO2 sequestration and wet season rice yield under tropical climatic conditions.