PSI-3 - Balance Between Productivity and Environmental Impacts of Grazed and Hay Fields

Abstract: Animal production has been associated with environmental impacts, but meat and dairy demand continuously increases. Grazed and hayfields have been responsible for enteric methane emissions, but also identified as great C stocks. Sustainable intensification, or balance between sustainability and productivity, is sought and we need to better understand the trade-offs to design appropriate management strategies. This study evaluated effects of grazed pastures and hayfields on carbon (C) stocks; and on soil GHG emissions (methane, CH4; nitrous oxide, N2O; and carbon dioxide, CO2), and forage dry matter and quality during four sampling periods (spring, early summer, late summer, and fall) of 2021. Forage samples were cut at stubble height, soil GHG emissions were monitored using static chamber methodology, and soil samples were collected from 0-100 cm. During the growing season, hayfields presented higher forage quality and lower forage production than grazed pastures. In addition, grazed pastures presented higher soil C stocks than hayfields. Hayfields presented lower CO2 emissions from soil in comparison to grazed pastures, suggesting slower decomposition of organic matter, which could be associated to lower C stocks. On the other hand, hayfields presented lower GHG emissions in comparison to grazed pastures, when considering CH4 and N2O emissions. Overall, a clear trade-off between the two types of fields is observed. Grazed pastures seem to be adding more C stocks over time, but also emitting more GHG emissions. Forage quality was also reduced. Hayfields had lower GHG emissions, but also lower C stocks. Forage quality was greater. In terms of long-term ecosystems' resilience and climate change mitigation, C addition from grazed pastures is more beneficial. In an eventual C market development, where C credits could be used or sold, grazing systems would be in advantage, again due to greater C stocks even if emitting slightly higher GHG emissions.