|dc.description.abstract||The disposal of organic wastes in landfills and applying nitrogen fertilizers to agricultural land cause multiple environmental issues. However, recycling organic wastes, e.g., biobased residues for agricultural use, is increasingly adopted to address landfill waste disposal and excessive nitrogen fertilizer use.
Objectives: The overall aim of this thesis was to explore the impact of biobased residues on soil health and greenhouse gas emissions under a changing climate - to provide alternative fertilizer sources for farmers to address soil health and reduce nitrogen fertilizer use (Chapter 1). The objective of Chapter 2 was to explore and integrate the conceptual and theoretical issues necessary for the biobased residues approach in addressing soil security concerns under a changing climate. The objective of Chapter 3 was to quantify the annual greenhouse gas emissions of a silt loam soil amended with nitrogen fertilizer and biobased residues under corn-soybean rotation. Chapter 4 builds upon Chapter 3 and explicitly evaluates the greenhouse gas emissions during the spring freeze-thaw events. Chapter 5 considers biobased residues' capacity to improve soil health in a temperate agricultural field in Ontario, Canada. Chapter 6 demonstrated how biobased residues, compared to nitrogen fertilizer, affect soil organic carbon stock and its associated fractions (active, slow, and passive) under continuous cropping and crop rotation in Ontario, Canada, using the Century model.
Methods: Chapter 2 is a literature review focused on establishing the links and assessment factors between sustainable indicators and biobased residues for soil security. Chapter 3 determined greenhouse gas emissions of soil amended with biobased residues (compost, biosolids, digestate) and nitrogen fertilizer under corn-soybean rotation in Elora Research Station, Ontario. Chapter 4 quantified greenhouse gas emissions, specifically during the spring freeze-thaw, where the soil was categorized as waterlogged, wet, or dry. Chapter 5 focuses on soil sampling and crop harvest carried out in autumn of each field season at a field site located in Elora, Ontario, Canada. Chapter 6 focuses on historical and current agroecosystem management practices in Elora, Ontario. This involved using the Century Soil Organic Matter model to predict future soil organic carbon stock changes using eight agroecosystem management practices.
Results and Discussion: Chapter 2 identified that biobased residues could address the underlying waste and agricultural issues, and more research on biobased residues dynamics in agricultural soil is critical. Chapter 3 demonstrated that biobased residues have a lower non-carbon dioxide (nitrous oxide and methane) emission than nitrogen fertilizer during the non-growing season. Chapter 4 showed that the dry phase during freeze-thaw, due to enhanced warming, caused intensified carbon dioxide flux compared to the wet and waterlogged freeze-thaw phase. Chapter 5 revealed that the soil health score of biosolids, nitrogen fertilizer, and all treatments combined contributed to one or more components of crop productivity. Chapter 6 demonstrated that agroecosystem management practices with compost and biosolids improved soil organic carbon's long-term (150 years) stabilization.
Overall Conclusions: biobased residues can function as an alternative for nitrogen fertilizer since they have the potential to mitigate greenhouse gas emissions, improve soil health, and increase the long-term stability of soil organic carbon that leads to carbon sequestration (Chapter 7).||en