Date of Graduation

12-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Environmental Dynamics (PhD)

Degree Level

Graduate

Department

Environmental Dynamics

Advisor/Mentor

Kristofor R. Brye

Committee Member

Roberts, Trenton L.

Second Committee Member

Henry, Christopher G.

Third Committee Member

Evans-White, Michelle

Fourth Committee Member

Lessner, Daniel J.

Keywords

furrow-irrigation, global warming potential, greenhouse gasses, rice, struvite

Abstract

Furrow-irrigation constitutes an alternative water regime that has been increasingly adopted in Arkansas. Among the management of nutrients in furrow-irrigated systems, phosphorus (P) represents a substantial challenge. The environmental sustainability of rice (Oryza sativa) production systems needs to be evaluated across different water regimes and fertilizer-P sources. Therefore, the objectives of the following studies were to: i) evaluate season-long carbon dioxide (CO2) and methane (CH4) emissions and global warming potential (GWP) under different tillage treatments [i.e., conventional tillage (CT) and no-tillage (NT)] and at different site positions (i.e., up-, mid-, down-slope) along the predominant slope of a production-scale, furrow-irrigated rice field in east-central Arkansas throughout the 2018 and 2019 growing seasons, ii) evaluate the environmental impact of electrochemically precipitated struvite (ECST) compared to other commonly used, commercially available fertilizer-P sources [i.e., triple superphosphate (TSP) and diammonium phosphate (DAP)], a commercially available chemically precipitated struvite (CPST), and an unamended control on season-long CO2, CH4, and nitrous oxide (N2O) emissions and GWP on rice grown under flooded conditions in the greenhouse in 2020 and 2021, iii) evaluate the effects of water regime (i.e., flooded and furrow-irrigated conditions) and fertilizer-P source [i.e., DAP, CPST, ECST, TSP, and an unamended control] on season-long CO2, CH4, and N2O emissions and GWP in the greenhouse in 2021, and iv) evaluate the effects of fertilizer source [i.e., ECST, CPST, TSP, DAP, environmentally smart nitrogen (ESN), and an unamended control] on season-long CO2, CH4, and N2O emissions and GWP in a furrow-irrigated rice field in east-central Arkansas in 2022. Gas samples were collected weekly in each growing season between planting and harvest using the enclosed-headspace, static-chamber approach. For Objective 1, in 2018, season-long CO2 (25391 kg CO2 ha-1) and CH4 (64.0 kg CH4 ha-1) emissions and estimated GWP (36396 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 (23496 kg CO2 ha-1) emissions were greatest from the down-slope/CT combination. For Objective 2, in both years, ECST had the numerically lowest GWP (7.41 and 7.61 Mg CO2 eq. ha-1 season-1 in 2020 and 2021, respectively). For Objective 3, mean season-long CH4 emissions were 10 times greater (P < 0.05) under flooded (29.4 kg CH4 ha-1 season-1) than under furrow-irrigated conditions (2.9 kg CH4 ha-1 season-1) and four times lower (P < 0.05) with ECST (3.4 kg CH4 ha-1 season-1) than other fertilizer-P sources, while mean GWP under furrow-irrigated conditions was almost 40% lower (P < 0.05) than under flooded conditions. For Objective 4, N2O emissions were lowest (P < 0.05) from ESN (1.50 kg ha-1 season-1), which did not differ from TSP, CPST, ECST, and DAP. Global warming potential was also lowest (P < 0.05) from ESN (1612 kg CO2 eq. ha-1 season-1), which did not differ from TSP, ECST, CPST, and DAP. Slow-release fertilizers, such as ECST, could be an effective mitigation tool to reduce GHG emissions from furrow-irrigated rice.

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