Climate-smart rice production using treated municipal wastewater: A two-year microcosm evaluation of surface and subsurface fertigation impacts on greenhouse gas emissions and productivity

The reuse of treated wastewater (TWW) offers a promising pathway for sustainable rice production, particularly in water-scarce regions. However, the environmental trade-offs associated with TWW fertigation require careful evaluation. This two-year microcosm study (2022–2023) investigated the effects of continuous surface irrigation (CSI) and continuous subsurface irrigation (CSSI) using TWW on greenhouse gas (GHG) emissions, rice productivity, and soil fertility, in comparison with conventional cultivation (CTRL). The irrigation regime significantly influenced GHG dynamics. In 2022, both TWW fertigation treatments increased overall GHG emissions relative to CTRL, whereas in 2023, CSI and CSSI recorded the lowest cumulative CH 4 and N 2 O emissions, with reductions of 32% and 125%, respectively. Despite this interannual variability, CSSI achieved the lowest yield-scaled GHG emissions by the end of the study, reaching 1 kg CO 2 -eq/kg grain, approximately half that of CTRL. Rice yields were comparable across treatments in 2022 but increased under CSI and CSSI in 2023 by 25% and 42%, respectively, relative to CTRL. Both fertigation systems also enhanced grain protein content without exceeding safety thresholds for heavy metal(loid)s, while maintaining soil nutrient status and organic matter despite the absence of synthetic fertilizers. These findings demonstrate the potential of TWW-based fertigation, particularly CSSI, as a climate-smart strategy for resource-efficient and fertilizer-free rice cultivation. Nevertheless, because this study was conducted under controlled microcosm conditions, field-scale validation is still required to confirm its applicability under variable environmental and management conditions. • TWW fertigation maintained or reduced CH 4 emissions compared to control • Subsurface irrigation reduced N 2 O emissions compared to surface and control systems • Subsurface TWW fertigation minimized yield-scaled GHG emissions • TWW fertigation improved grain yield and protein content without heavy metal risks • TWW fertigation preserved soil fertility and organic matter across two seasons