Md. Khairul Alam1, Richard W. Bell1, Wahidul K. Biswas2
1 Land Management Group, School of Veterinary and Life Sciences, Murdoch University, Western Australia 6150, Australia
2 Sustainable Engineering Group, School of Civil and Mechanical Engineering, Curtin University, Bentley, Western Australia 6845, Australia
Nitrous oxide (N2O) production and emission under wetland rice (Oryza sativa L.) is difficult to predict due to the trade-off between methane (CH4) and N2O emissions for different establishment and management practices. Any novel technology with the potential to reduce the emissions of both CH4 and N2O under wetland rice could make a significant contribution to total agricultural global warming mitigation. A streamlined life cycle assessment (LCA) approach to quantify the C footprint of rice production process in the Eastern Gangetic Plains (EGP) was adopted. The GHG emissions from one tonne of rice production were studied for the following cropping practices: a) conventional puddled transplanting with low residue retention (CTLR); b) conventional puddled transplanting with high residue retention (CTHR); c) unpuddled transplanting following strip tillage with low residue retention (UTLR) and; d) unpuddled transplanting with high residue retention (UTHR). Total pre–farm and on–farm emissions for 1 tonne of rice production amounted to 1.11, 1.19, 1.33 and 1.57 tonne CO2–eq for UTLR, UTHR, CTLR and CTHR, respectively, in the 100-year time horizon. For all four treatments, the predominant GHG emission was soil CH4 (comprising 60-67% of the total) followed by emission from on-farm machinery use. The UTLR was the most effective GHG mitigation option (it saved 29% of the total GHG emissions in comparison with CTHR) in wetland rice production. N2O emission contributed 2–3.5% to the total on–farm GHG emitted for rice production of which the lowest portion was shared by UTLR and UTHR. The UTLR reduced both CH4 and N2O emissions simultaneously. The novel minimum tillage establishment approach for rice followed by UT has potential to increase global warming mitigation of wetland rice in the EGP, but further research is needed to assess the contributions of N2O in the LCA of rice production in other similar rice growing areas.