190 Effects of Flooding on Grazed Pastures: Forage Quality, GHG Emissions and C Stocks

Abstract

Abstract Manure creates hot spots of nutrients concentration, and consequently nutrient losses to air and water. In flood-prone areas these losses represent a major concern for environment. However, there is a gap on the understanding of the effects of recurring, short-term flooding on environmental and forage characteristics. This study evaluated the effects flooding on soil carbon (C) stock; and greenhouse gas (GHG) emissions (methane, CH4; nitrous oxide, N2O; and carbon dioxide, CO2) from soil; and forage dry matter and quality in flooded and non-flooded grazed pastures during four sampling periods (spring, early summer, late summer, and fall) of 2021. Soil samples were collected from 0-100cm, forage samples were cut at stubble height and soil greenhouse gases (GHG) emissions were monitored using the static chamber methodology. Preliminary results show trends of reduced forage digestibility in flooded pastures. No differences were observed on forage dry matter. Overall, there was no differences between CO2 emission from soil in flooded and non-flooded areas. Soil CH4 fluxes were primarily negative, and flooding seems to reduce the sink potential for CH4 from soil, except during early summer. For N2O the effects of season were very pronounced, increased emissions from spring to early summer and throughout fall in both flooded and non-flooded pastures. We did not observe any N2O sinks, and no difference between treatments. Flood-prone pastures had decreased C stock in comparison with non-flood pastures. Preliminary results show that forage production may represent a good option for flooded areas, since no effects were observed on mass and few effects on quality. However, flooding reduced C stock potential and CH4 sinks. A second sampling season will be performed in 2022 to further observe these results and allow for C-equivalent flux calculations. The balance between productivity and environmental impacts of flood-prone pastures will then be assessed.