Date of Award

9-1-2025

Degree Type

Thesis

Degree Name

Master of Science (M.S.)

Department

Biological Sciences

First Advisor

Dafeng Hui

Abstract

Agriculture contributes considerably to global greenhouse gas (GHG) emissions, requiring sustainable methods for tackling climate change. This thesis includes two mega-analyses and one field experiment to investigate the impact of conservation tillage and soil amendments on crop productivity and greenhouse gas emissions. The first mega-analysis combined data from 30 meta-analyses to assess the impact of no-tillage (NT), reduced-tillage (RT), and combination NT+RT on crop yields and soil GHG emissions. NT decreased yields by 3.3% and increased N₂O emissions by 8.7%, but RT and NT+RT had no effect. The second mega-analysis found that both NT and RT considerably increased soil organic carbon (SOC), particularly in climates, longer durations, and with residue retention. The field study compared the effects of biochar (0, 11, and 22 t ha⁻¹) and nitrogen fertilization (0 and 80 kg N ha⁻¹) on switchgrass biomass productivity and soil N₂O emissions. Biochar, particularly at 22 t ha⁻¹ without nitrogen, leads to increased N₂O emissions due to higher soil temperatures, increased moisture, and lower nitrogen uptake. Fertilized plots showed higher biomass and lower N₂O variability, likely due to improved nitrogen utilization. Correlation analysis indicated a substantial correlation between N₂O emissions and temperature. Overall, the effectiveness of conservation tillage and biochar application in lowering GHG emissions was context-dependent and influenced by various factors, including climate, soil type, and nutrient management. These results offer insights into the balance between crop productivity and environmental sustainability in bioenergy cropping systems.

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