Greenhouse Gas Emissions from an Intensive Grassland: Key Driving Variables

 Since the industrial revolution the temperature of the Earth atmosphere has been increasing leading to observed global warming. Increases in the greenhouse gases (GHG) concentration in the atmosphere like carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) are appointed to be responsible for this changes. In the livestock system based on grassland a large amount of these gases can be emitted. A few quantifications of these GHG emissions and key driving controlling their production were carried out. This research objectivized to evaluate the key driving variables involved in the GHG emissions from a tropical soil cultivated with grass. The experiment was performed at São Paulo State University during three years (2012-2014). The GHG emissions were measured using static closed chamber methodology and quantification by gas chromatography. To identify the keys driving variables explaining the GHG fluxes a principal component analysis (PCA) was run. The variables analyzed were pasture height, precipitation, soil moisture, soil ammonium, soil nitrate and the GHG fluxes. Two principal components, precipitation and pasture height, explained 44.74% of the cumulative variance. Within components for CO₂ fluxes, a significant correlation was found with pasture height (0.57; P < 0.001) and soil moisture (0.36; P < 0.01). For CH₄ emissions, a strong correlation was found with precipitation (-0.80; P < 0.001) followed with CO₂. While N₂O fluxes was correlated with precipitation (0.48; P < 0.001) and soil ammonium (0.36; P < 0.05). The GHG fluxes maybe were explained by the moisture that is an important issue for microorganism life and chemical reactions of the carbon and nitrogen cycles. Pasture height possibly explained the CO₂ fluxes because of the leaf area variation among the pastures which influence the photosynthesis. CH₄ emissions could be associated with CO₂ fluxes because of this gas in certain conditions is oxidized and produces CH₄. The key driving variables involved in the GHG emissions were soil moisture and pasture height, precipitation and CO₂ fluxes, precipitation and soil ammonium for CO₂, CH₄ and N₂O, respectively.