Review of research studies on nitrous oxide emissions from manure-amended soils in Canada from 1990 to 2023

Nitrous oxide (N 2 O) emissions from manure-amended soils are estimated to be 1525 kt CO 2 e in Canada. The accuracy of this estimate is dependent on emission measurements. However, obtaining accurate measurements is challenging due to the variable distribution of livestock types, climates, soils, and management across Canada. This study compares research studies on the temporal and spatial distribution of N 2 O emissions from land applied manure with emission estimates from the National Inventory Reports to evaluate how research aligns with key factors driving emissions. Overall, 122 articles were identified, including 31 incubation, 57 soil chamber, and 8 micrometeorological studies (the rest were modelling). Although 51 (42%) of the articles were based in Ontario and Quebec, this region still warrants more attention, because its high livestock population and humid climate results in 68.7% of Canada's N 2 O emissions from manure-amended soil. Dairy manure was most common with 55 studies, followed by swine (36) and beef (29). Emissions from beef manure applications are notably lacking in Quebec, while dairy and swine studies were reasonably aligned with provincial emissions. The underutilization of micrometeorological methods creates a significant gap in determining annual emissions. Increasing research focus on year-round and non-growing seasons would improve estimates. Additional studies using solid manure and/or a wider range of soil textures would strengthen the national emission estimate, which currently relies mostly on research involving liquid manure and medium-textured soils. Further research is needed to fill the identified gaps; specifically, high-resolution measurements, considering local livestock industries, and soil textures in humid climates.