Agricultural Greenhouse Gas Emissions under Different Cover Crop Systems Público

Abstract

Cultivated lands that support high productivity have the potential to produce a large amount of GHG emissions, including carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4). Intensive land management practices can stimulate CO2, N2O, and CH4emissions from the soil. Cover crop establishment is considered as one of the sustainable land management strategies under warm and humid environmental conditions. To better understand how the incorporation of cover crops affect three major GHGs, in this study,we compared trace gas fluxes in three cover crop systems (CC, CR, and LM) and a no cover crop (Tr) system in a no-till maize field over the whole growing season in 2018. In 2019, we further explored potential differences for the same three GHGs between in-row and between-row of maize for LM and Tr systems during the early growing season. Measurements were taken using a cavity ring-down spectroscopy gas analyzer in Watkinsville, GA. In 2018, the highest fluxes of both CO2 (6.07 µmol m^-2s^-1) and N2O (2.10 µmol m^-2hr^-1) were from LM between row. The maximum N2O fluxes observed in LM on June 20^thin 2018 was when soil N increase was the largest. Soils served as sinks for CH4but Tr system was the smallest CH4sink compared to the other three cover crop systems. In our previous work conducted in 2016, we observed a statistically significant difference between LM and Tr only in between the rows of maize. In 2019, however, we observed significantly higher CO2emissions in LM compared to Tr, also in the rows of maize. This difference could be related to the difference in measurement techniques and soil C content due to the three-year incorporation of LM. For N2O, the highest emissions were observed from TrIR (3.93 µmol m²hr^-1) in 2019 with greater N inputs. In 2019, we observed a smaller CH4sink in TrIR (-0.08 µmol m²hr^-1) compared to TrBWR (-0.61 µmol m²hr^-1) due potentially to greater NH4⁺inhibition effects on CH4consumption from greater N fertilizer inputs. Comparing four agricultural practices with a net CO2e in 2018, mitigation effects from CH4sink, soil carbon sequestration, reduced fertilizer and herbicide application are still not capable of counteracting higher CO2and N2O emissions generated in the field. The net CO2e from CC, CR, WC, and Tr were 17,323, 17,129, 30,101, and 11,402 kg ha^-1 yr^-1, respectively. 

Table of Contents

INTRODUCTION   1

METHODS     3

SOIL DESCRIPTION AND EXPERIMENTAL DESIGN   3

SOIL SAMPLING AND GHG FLUX MEASUREMENTS5

DATA ANALYSIS   6

STATISTICS    6

RESULTS7

GHG FLUXES IN 2018   7

GHG FLUXES IN 2019   13

GHG FLUXES IN TRIR PLOTS IN 201919

DISCUSSION  22

CO2 AND N2O FLUX    22

CH4 FLUX      23

CONCLUSION       25

REFERENCES  26

About this Master's Thesis

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School	Laney Graduate School
Department	Environmental Sciences
Degree	M.S.
Submission	Master's Thesis
Language	English
Research Field	Climate Change
Palavra-chave	Greenhouse Gas Emissions
Committee Chair / Thesis Advisor	Eri Saikawa, Emory University
Committee Members	Debjani Sihi, Emory University Eri Saikawa, Emory University Carolyn Keogh, Emory University

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