CH4 Fluxes Over Livestock in a Natural Grassland in the Southern Brazil Pampa Biome

Estimates show that livestock production is responsible for more than 50% of greenhouse gas (GHG) emissions related to agriculture in Brazil. In southern Brazil, beef production is carried out on natural pastures of the Pampa biome, composed of a large number of native grasses and legumes. The conservation and sustainable use of the Pampa biome through the proper management of extensive cattle raising can significantly contribute to the mitigation of GHG when systems with rest between pastures, such as the rotational management system, are adopted. In this work, CH4 fluxes were measured using the Eddy Covariance (EC) methodology in a livestock area in natural grassland of the Pampa biome under a rotational management system from September 2018 to September 2020 (Y1= Sep 2018 to Sep 2019; Y2 = Sep 2019 to Sep 2020). CH4 showed lower values during spring and summer and higher values during autumn and winter. The daily average of CH4 fluxes in periods without cattle inside the flux tower footprint was 0.004 gCH4 m-2 d-1 while with cattle it was 0.024 gCH4 m-2 d-1, that is, the period with cattle emitted more than five times than the period without. Integrating annually, Y2 had CH4 emissions 42% higher than Y1 (Y1 = 3.1 gCH4 m-2; Y2 = 4.4 gCH4 m-2). As it is a drier year, Y2 had less biomass availability, which meant that the number of days with the presence of cattle in the paddocks was 44% higher. Therefore, the difference between Y1 and Y2 emissions may be exclusively due to the increased presence of animals at the site and the lower quality of forage available for grazing. These results show that cattle raising in the Pampa biome has low CH4 emissions and has even greater reduction potential according to the management and quality of the offered pasture. Thus, it is of fundamental importance that assessments using the EC methodology are extended to periods with different climatic conditions and different livestock management systems in the Pampa biome in order to identify the forms of production that mitigate GHG emissions, valuing such a production system and preserving the native vegetation of the biome.