Seasonal Greenhouse Gas and Soil Nutrient Cycling in Semi-Arid Native and Non-Native Perennial Grass Pastures.

Previous research indicates that photosynthetic metabolism of warm- and cool-season grass species affects greenhouse gas (GHG, (carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O))) emissions from soil. Monitoring seasonal variability of GHG and soil carbon (C) and nitrogen (N) from Central Oklahoma soils cropped with warm- or cool-season grasses has not been assessed. This information could provide establish best management practices to mitigate GHGs and store soil C and N. We hypothesized that the magnitude of labile soil C and N would increase with soil moisture followed by an increase in GHG emissions in cool-season pasture soils early in the growing season compared to warm-season pasture soils. Soils under warm-season grasses will experience a similar pattern but later in the growing season. A study at the USDA-ARS Grazinglands Research Laboratory, El Reno, OK was conducted in warm-season and cool-season grasses to: 1) determine seasonal soil C and N content and 2) obtain seasonal GHG emissions of soils under warm- and cool-season grasses. Bi-weekly sampling of GHG and soil (0-15cm) occurred in warm- and cool-season pastures in replicates of five. Greenhouse gas samples were analyzed for CO₂, CH₄ and N₂O on a gas chromatograph. Soil water content (SWC), physical properties and labile C and N were determined using standard methods. Initial results indicate that the magnitude of CO₂ and N₂O were proportional to SWC, and CH₄ assimilation decreased in semi-arid soils under native perennial grasses compared to soils under non-native grasses. Soils under non-native grasses had increased magnitudes of CO₂ and N₂O, while CH₄ assimilation was similar to soil under native grasses during warmer seasonal trends were moisture was limited. The implication of this research indicates that GHG fluxes from soils in semi-arid environments are altered by abiotic drivers and assimilate CH₄.