Degree

Doctor of Philosophy (PhD)

Department

School of Plant, Environmental Management and Soil Sciences

Document Type

Dissertation

Abstract

Understanding and enhancing soil quality is essential for improving crop production resilience to climate change. This study investigates nitrogen (N) dynamics and soil health in subtropical rice production systems of Louisiana, comparing conventional delayed-flood rice (DFR) and emerging furrow-irrigated rice (FIR) cultivation methods. The research addresses critical knowledge gaps in understanding how water management practices and N fertilization impact soil organic matter (SOM) composition, enzyme activities, and greenhouse gas (GHG) emissions in these systems. Biological soil health indicators were evaluated across different soil types, revealing strong relationships between CO2-Burst test results, alkali-hydrolyzable nitrogen (AHN), and rice productivity in DFR systems, which could be used to adjust N fertilizer recommendation. A critical CO2-Burst threshold of 55 mg C kg-1 was identified, above which rice yields plateaued from native N supply. Comparative analysis of soil enzyme activities between DFR and FIR systems demonstrated generally higher activities in FIR, particularly for β-glucosidase, β-glucosaminidase, and arylsulfatase, indicating enhanced nutrient cycling potential. Advanced spectroscopic techniques (13C NMR and FTIR) revealed distinct differences in SOM chemistry between DFR and FIR systems. Longer flooding period in DFR promoted more aliphatic and lignin structures, while FIR showed evidence of enhanced oxidation and decreased condensation of organic matter. Nitrogen fertilization further altered organic matter composition, with more pronounced effects under furrow irrigation. DNDC model simulations provided insights into long-term trends of rice yield and methane (CH4) emissions under various management scenarios and climate change projections. The model predicted severe negative impacts on rice yields due to increasing temperatures, with potential yield reductions up to 59% under a 7°C warming scenario projected for 2100. Alternate wetting and drying (AWD) practices showed potential to significantly reduce CH4 emissions while maintaining yields. This research has important implications for sustainable rice production in subtropical regions, supporting the integration of biological soil health assessments into N management strategies and highlighting the need for climate change adaptation. The findings provide a foundation for developing more sustainable and resilient rice cultivation practices balancing productivity goals with environmental stewardship.

Date

7-16-2024

Committee Chair

Jim J. Wang

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Available for download on Friday, July 16, 2027

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Soil Science Commons

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