Date of Graduation

8-2024

Document Type

Thesis

Degree Name

Master of Science in Crop, Soil & Environmental Sciences (MS)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Brye, Kristofor R.

Committee Member

Roberts, Trenton L.

Second Committee Member

Adams, Richard

Third Committee Member

Wood, Lisa S.

Keywords

Furrow-irrigated; Greenhouse gas; Rice; Struvite

Abstract

Over time, as the influences of climate-change and declining, mineable, global phosphorus (P) reserves begin to impact agricultural production systems, alternative fertilizer sources and management practices, such as struvite (MgNH4PO4 · 6H2O) and furrow-irrigation, will be necessary to accommodate nutrient and water demands. The precipitation and use of struvite as a fertilizer-P source could reduce environmental damages caused by nutrient-rich wastewater streams, supplement domestic P supply, and improve the sustainability of flood-, and furrow-irrigated rice production by reducing greenhouse gas emissions. The study of struvite from both chemical and electrochemical precipitation processes is well documented, but currently there is a gap in the literature regarding the use of electrochemically precipitated struvite (ECST)-P sources created from actual municipal wastewater in agricultural production systems and the resulting impacts on crop and greenhouse gas (GHG) production. Thus, the objectives of this study were to i) quantify GHG [i.e., methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2)] fluxes, season-long emissions, and global warming potential (GWP) from a chemically precipitated struvite (CPST) and a synthetic and a real-wastewater-derived ECST compared to monoammonium phosphate (MAP) and an unamended control (UC) from floodirrigated rice (Oryza sativa) grown in a P-deficient silt-loam soil in the greenhouse during the 2022 growing season and ii) to quantify CH4, N2O, CO2 fluxes, season-long emissions, global warming potential (GWP), emissions intensity, plant response, and end-of-season soil properties from a synthetic and a real-wastewater-derived ECST and a CPST compared to MAP and an UC from simulated furrow-irrigated rice cultivated in a P-deficient silt-loam soil in the greenhouse during the 2023 growing season. Gas collection occurred weekly over a 140-day period during the 2022 growing season and over a 162-day period during the 2023 growing season for the flood- and furrow-irrigated studies, respectively. For the 2022 study, season-long CH4 emissions differed among fertilizer-P treatments and were smallest from the UC (29.9 kg CH4 ha-1 ), which was similar to both ECST-P sources. Additionally, the CO2-excluded GWP from the 2022 study was greatest from MAP (2881 kg CO2-equivalents ha-1 ), which was similar to CPST, and smallest from the UC (978 kg CO2-equivalents ha-1 ), which did not differ from either ECST-P source. Season-long emissions for N2O differed among fertilizer-P treatments for the 2023 simulated furrow-irrigation study and were greatest from the UC (6.1 kg N2O ha-1 ), which differ from and was at least 2.8 times greater than all other fertilizer-P treatments. For the 2023 study, for the vast majority of plant response properties and all GHG properties, ECSTSyn and ECSTReal did not differ from each other and rarely differed from MAP. Results of this study emphasized the possible agronomic and environmental benefits of struvite, both as CPST and ECST, as an efficient fertilizer-P source to improve the sustainability of both flood- and furrow-irrigated rice production in Arkansas. Additionally, as the majority of properties were similar between the two ECST fertilizer-P sources, results of this study indicate the comparability of ECST fertilizers created from actual wastewater to previously studied ECST fertilizer-P sources.

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