PSXI-4 Effect of annual forage diversity on soil nitrous oxide emissions in semiarid Canadian Prairies

Abstract Nitrogen transformation, either from organic amendments or synthetic fertilizers, contributes to nitrous oxide (N2O) emission, a potent greenhouse gas from agricultural soils. In grazing systems, N2O emissions can occur in both stages of production, during the forage growth phase mainly related to fertilizer use and residue transformations as well as the animal phase from animal excreta deposition and transformation. Different management practices with potential to reduce N2O emissions, including the adoption of diverse forage mixtures (poly cropping) has gained attention. Poly cropping can promote high resource use efficiency and influence edaphic-climatic conditions, major controllers for soil N2O emissions. However, information on the effect of poly cropping on soil N2O emissions in the Canadian Prairies under semiarid climate and Brown Chernozem soils is limited. The overall objective of this study was to explore the potential of using poly crop mixtures as an alternative feed source for Canadian beef cattle and its impact on soil N2O emissions. Three treatments were considered: i) control, forage oat monoculture, ii) simple mix, containing four different annual forage species (forage oat, forage pea, forage brassica, and hairy vetch), and iii) complex mix containing eight annual forage species (forage oat, forage pea, barley, forage brassica, hairy vetch, red proso millet, teff grass, and, chicory). Treatments were established in a completely randomized block design scheme with three replicates. The study was conducted at the Swift Current Research and Development Centre, the driest climatological condition in the Canadian Prairies. Following pre-seeding field preparation, treatments were established by the end of May and Urea Phosphate (34-17-0) fertilizer was split-applied at 112 kg/ha. Nitrous oxide emission was measured over the crop phase in 2023 growing season, the first year of a 3-yr trial, using the manual chamber method. Furthermore, ancillary measurements were performed. During the 2023 crop growth phase, N2O emissions ranged from 446 to 610 g Nּ ha-1, and were not affected by treatments. Soil inorganic N was greater in parts of the season for the complex mix, but that did not translate into greater cumulative N2O emissions. Overall, the treatments did not affect soil volumetric water content in the topsoil, a key factor dictating N2O emissions. This project will continue until 2026 and capture emissions from different seasons including major spring-thaw. In those years, measurements will also be extended to an on-farm sites involving farmers situated in contrasting edaphic-climatic conditions of the Canadian Prairies.