Net ecosystem exchange of carbon, greenhouse gases, and energy budget in coastal lowland double cropped rice ecology

Abstract

Rice (Oryza sativa) based cropping in the Asian region is considered as one of the most significant agricultural practices that contribute to climate change due to high energy use and carbon footprints (CF). To assess the contributions of rice-based cropping in lowland coastal ecosystems to environmental change, energy budgets, CF, exchange of CO2 and fluxes of non-CO2 greenhouse gases (GHGs) were determined for an array of conservation tillage practices under rice-rice (RR) and rice-cotton (Gossypium hirsutum) (RC) systems as main plot treatments, tillage intensity [zero tillage (ZT), reduced tillage (RT), conventional tillage (CT)] as sub-plot treatments, and residue (R) or no residue (NR) as sub-sub plot treatments. The energy use was calculated operation-wise and RT was recorded to be most efficient in terms of energy utilization. Rice-based cropping system enhanced soil organic carbon (SOC) at the rate of 0.22 to 0.69, and 0.09 to 0.45 Mg ha−1yr−1 in rice-rice and rice-cotton systems, respectively, with the exception of RC-ZTNR which depleted SOC by 0.11 Mg ha−1yr−1. Static chamber-gas chromatography-based methodology along with biometric data collection was used for the carbon and GHG budgeting. The evaluation of net ecosystem carbon budget (NECB, based on net ecosystem exchange of CO2 and non-CO2 carbon via crop harvest, CH4-C, C inputs to soils and C loss through runoff), and GHG budget (GHGB, adding CH4 and N2O fluxes, and emissions from inputs used to the NECB on CO2 equivalent basis) showed that the rice-based cropping systems in lowland coastal ecologies functioned as carbon sinks (NECB:1523 and 944 Kg C ha−1yr−1 in rice-rice and rice-cotton system, respectively) but GHG source except under reduced tillage with residue (RTR) management which was a GHG sink (−68 to −228 Kg CO2-eq ha−1yr−1). The treatment RTR also recorded the least CF, and highest ecosystem service values of climate regulation among all tillage practices.