Evaluation of site position and tillage effects on global warming potential from furrow-irrigated rice in the mid-southern USA

Dynamic and spatially variable environmental conditions within furrow-irrigated rice (Oryza sativa) systems can exacerbate greenhouse gas (GHG) production. Few studies have been conducted to evaluate the combined emissions of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) from furrow-irrigated rice production. The objective of this field study was to evaluate estimated global warming potential (GWP) over two growing seasons (2018 and 2019) under conventional tillage (CT) and no-tillage (NT) and at up-, mid-, and down-slope positions in a production-scale, furrow-irrigated rice field on a silt-loam soil (Typic Albaqualfs). Gas samples were collected weekly between planting and harvest using enclosed-headspace, static chambers. In 2018, season-long CO2 (25,391 kg CO2 ha- 1), and CH4 (64.0 kg CH4 ha- 1) emissions and estimated GWP (36,396 CO2 eq.) were greater from the down- than the up- and mid-slope positions. In 2019, season-long CH4 emissions (85.0 kg CH4 ha- 1) were greatest from the down-slope position, while CO2 (23,496 kg CO2 ha- 1) emissions were greatest from the down-slope/CT combination. In 2018, GWP from CT was 25% greater than from NT, and 75 and 59% greater at the down- than at the up- and mid-slope positions, respectively, while GWP in 2019 was only numerically greater from CT than from NT. Results suggested that, unless environmental conditions involve flooding, NT could be a useful mitigation practice for reducing both CH4 and N2O emissions. Results also suggested that GHG and GWP mitigation could be accomplished by tailoring management practices to the various site positions in a production-scale, furrow-irrigated rice field.