Date of Award

2022

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Natural Resources

First Advisor

Carol Adair

Abstract

Agricultural best management practices (BMPs) promote soil health and achieve multiple positive environmental outcomes. However, practices that are intended to solve one environmental challenge may have unintended climate impacts, therefore presenting a potential tradeoff. For example, manure injection is a BMP that can reduce runoff and nitrogen loss as ammonia gas (NH3) but can increase N2O and CO2 emissions compared to manure broadcast application. This thesis explores how CO2 and N2O emissions from manure injection compare to other soil fertility practices as well as the conditions that may enhance or reduce these greenhouse gas (GHG) fluxes. First, during a two-year field trial in a Northeast hayfield, we applied different nitrogen sources (manure and synthetic urea) and application methods (manure injection and manure broadcast) with or without a urease inhibitor and measured the resulting GHG fluxes, soil mineral nitrogen availability, environmental conditions, and yield (Chapter 1). We found that nitrogen source and manure application method minimally impacted daily and cumulative N2O and CO2 emissions and that the primary drivers were instead related to environmental conditions – soil moisture or temperature – and nitrogen availability. Second, we examined how manure injection could interact with no-till, a BMP that enhances soil aggregation, to influence GHG emissions (Chapter 2). During a lab-based soil incubation, we measured N2O and CO2 fluxes after manure was injected into soil cores that either contained soil aggregates of two different size categories or structureless soil (i.e., aggregates destroyed in a blender). GHG fluxes were comparable across treatments on most days, but the structureless soil produced elevated N2O fluxes in the last few days of our experiment, suggesting that aggregation could play a role in mediating N2O emissions from manure injection. Overall, this thesis contributes to a broader understanding of the benefits and tradeoffs of BMPs as well as the conditions driving agricultural GHG emissions.

Language

en

Number of Pages

73 p.

Available for download on Wednesday, July 19, 2023

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